Prolegomena to Any Future Metaphysics | Immanuel Kant

| sábado, 7 de novembro de 2009
These Prolegomena are destined for the use, not of pupils,
but of future teachers, and even the latter should not expect
that they will be serviceable for the systematic exposition of a
ready-made science, but merely for the discovery of the science

Prolegomena to Any Future Metaphysics

Immanuel Kant

Copyright 1997, James Fieser ( See endnote for
details on copyright and editing. The following is based on Paul
Carus's 1902 translation of the Prolegomena. Spelling has been
Americanized. A few of Lewis White Beck's conventions have been
adopted from his revision of Carus's translation, such as
replacing the word "cognise" with "knowledge."1


Preamble On The Peculiarities Of All Metaphysical Cognition.
First Part Of The Transcendental Problem: How Is Pure
Mathematics Possible?
Second Part Of The Transcendental Problem: How Is The
Science Of Nature Possible?
Third Part Of The Main Transcendental Problem: How Is
Metaphysics In General Possible?
Conclusion: On The Determination Of The Bounds Of Pure
Solution Of The General Question Of The Prolegomena: "How
Is Metaphysics Possible As A Science?"
Appendix: On What Can Be Done To Make Metaphysics Actual As
A Science.

* * * *


These Prolegomena are destined for the use, not of pupils,
but of future teachers, and even the latter should not expect
that they will be serviceable for the systematic exposition of a
ready-made science, but merely for the discovery of the science

There are scholarly men, to whom the history of philosophy
(both ancient and modern) is philosophy itself; for these the
present Prolegomena are not written. They must wait till those
who endeavor to draw from the fountain of reason itself have
completed their work; it will then be the historian's turn to
inform the world of what has been done. Unfortunately, nothing
can be said, which in their opinion has not been said before, and
truly the same prophecy applies to all future time; for since the
human reason has for many centuries speculated upon innumerable
objects in various ways, it is hardly to be expected that we
should not be able to discover analogies for every new idea among
the old sayings of past ages.

My object is to persuade all those who think Metaphysics
worth studying, that it is absolutely necessary to pause a
moment, and, neglecting all that has been done, to propose first
the preliminary question, 'Whether such a thing as metaphysics be
at all possible?'

If it be a science, how comes it that it cannot, like other
sciences, obtain universal and permanent recognition ? If not,
how can it maintain its pretensions, and keep the human mind in
suspense with hopes, never ceasing, yet never fulfilled? Whether
then we demonstrate our knowledge or our ignorance in this field,
we must come once for all to a definite conclusion respecting the
nature of this so-called science, which cannot possibly remain on
its present footing. It seems almost ridiculous, while every
other science is continually advancing, that in this, which
pretends to be Wisdom incarnate, for whose oracle every one
inquires, we should constantly move round the same spot, without
gaining a single step. And so its followers having melted away,
we do not find men confident of their ability to shine in other
sciences venturing their reputation here, where everybody,
however ignorant in other matters, may deliver a final verdict,
as in this domain there is as yet no standard weight and measure
to distinguish sound knowledge from shallow talk.

After all it is nothing extraordinary in the elaboration of
a science, when men begin to wonder how far it has advanced, that
the question should at last occur, whether and how such a science
is possible? Human reason so delights in constructions, that it
has several times built up a tower, and then razed it to examine
the nature of the foundation. It is never too late to become
wise; but if the change comes late, there is always more
difficulty in starting a reform.

The question whether a science be possible, presupposes a
doubt as to its actuality. But such a doubt offends the men whose
whole possessions consist of this supposed jewel; hence he who
raises the doubt must expect opposition from all sides. Some, in
the proud consciousness of their possessions, which are ancient,
and therefore considered legitimate, will take their metaphysical
compendia in their hands, and look down on him with contempt;
others, who never see anything except it be identical with what
they have seen before, will not understand him, and everything
will remain for a time, as if nothing had happened to excite the
concern, or the hope, for an impending change.

Nevertheless, I venture to predict that the independent
reader of these Prolegomena will not only doubt his previous
science, but ultimately be fully persuaded, that it cannot exist
unless the demands here stated on which its possibility depends,
be satisfied; and, as this has never been done, that there is, as
yet, no such thing as Metaphysics. But as it can never cease to
be in demand,2 -- since the interests of common sense are
intimately interwoven with it, he must confess that a radical
reform, or rather a new birth of the science after an original
plan, are unavoidable, however men may struggle against it for a

Since the Essays of Locke and Leibniz, or rather since the
origin of metaphysics so far as we know its history, nothing has
ever happened which was more decisive to its fate than the attack
made upon it by David Hume. He threw no light on this species of
knowledge, but he certainly struck a spark from which light might
have been obtained, had it caught some inflammable substance and
had its smoldering fire been carefully nursed and developed.

Hume started from a single but important concept in
Metaphysics, viz., that of Cause and Effect (including its
derivatives force and action, etc.). He challenges reason, which
pretends to have given birth to this idea from herself, to answer
him by what right she thinks anything to be so constituted, that
if that thing be posited, something else also must necessarily be
posited; for this is the meaning of the concept of cause. He
demonstrated irrefutably that it was perfectly impossible for
reason to think a priori and by means of concepts a combination
involving necessity. We cannot at all see why, in consequence of
the existence of one thing, another must necessarily exist, or
how the concept of such a combination can arise a priori. Hence
he inferred, that reason was altogether deluded with reference to
this concept, which she erroneously considered as one of her
children, whereas in reality it was nothing but a bastard of
imagination, impregnated by experience, which subsumed certain
representations under the Law of Association, and mistook the
subjective necessity of habit for an objective necessity arising
from insight. Hence he inferred that reason had no power to think
such, combinations, even generally, because her concepts would
then be purely fictitious, and all her pretended a priori
cognitions nothing but common experiences marked with a false
stamp. In plain language there is not, and cannot be, any such
thing as metaphysics at all.3

However hasty and mistaken Hume's conclusion may appear, it
was at least founded upon investigation, and this investigation
deserved the concentrated attention of the brighter spirits of
his day as well as determined efforts on their part to discover,
if possible, a happier solution of the problem in the sense
proposed by him, all of which would have speedily resulted in a
complete reform of the science.

But Hume suffered the usual misfortune of metaphysicians, of
not being understood. It is positively painful to see bow utterly
his opponents, Reid, Oswald, Beattie, and lastly Priestley,
missed the point of the problem; for while they were ever taking
for granted that which he doubted, and demonstrating with zeal
and often with impudence that which he never thought of doubting,
they so misconstrued his valuable suggestion that everything
remained in its old condition, as if nothing had happened.

The question was not whether the concept of cause was right,
useful, and even indispensable for our knowledge of nature, for
this Hume had never doubted; but whether that concept could be
thought by reason a priori, and consequently whether it possessed
an inner truth, independent of all experience, implying a wider
application than merely to the objects of experience. This was
Hume's problem. It was a question concerning the origin, not
concerning the indispensable need of the concept. Were the former
decided, the conditions of the use and the sphere of its valid
application would have been determined as a matter of course.

But to satisfy the conditions of the problem, the opponents
of the great thinker should have penetrated very deeply into the
nature of reason, so far as it is concerned with pure thinking,-a
task which did not suit them. They found a more convenient method
of being defiant without any insight, viz., the appeal to common
sense. It is indeed a great gift of God, to possess right, or (as
they now call it) plain common sense. But this common sense must
be shown practically, by well-considered and reasonable thoughts
and words, not by appealing to it as an oracle, when no rational
justification can be advanced. To appeal to common sense, when
insight and science fail, and no sooner-this is one of the subtle
discoveries of modern times, by means of which the most
superficial ranter can safely enter the lists with the most
thorough thinker, and hold his own. But as long as a particle of
insight remains, no one would think of having recourse to this
subterfuge. For what is it but an appeal to the opinion of the
multitude, of whose applause the philosopher is ashamed, while
the popular charlatan glories and confides in it? I should think
that Hume might fairly have laid as much claim to common sense as
Beattie, and in addition to a critical reason (such as the latter
did not possess), which keeps common sense in check and prevents
it from speculating, or, if speculations are under discussion
restrains the desire to decide because it cannot satisfy itself
concerning its own arguments. By this means alone can common
sense remain sound. Chisels and hammers may suffice to work a
piece of wood, but for steel-engraving we require an engraver's
needle. Thus common sense and speculative understanding are each
serviceable in their own way, the former in judgments which apply
immediately to experience, the latter when we judge universally
from mere concepts, as in metaphysics, where sound common sense,
so called in spite of the inapplicability of the word, has no
right to judge at all.

I openly confess, the suggestion of David Hume was the very
thing, which many years ago first interrupted my dogmatic
slumber, and gave my investigations in the field of speculative
philosophy quite a new direction. I was far from following him in
the conclusions at which he arrived by regarding, not the whole
of his problem, but a part, which by itself can give us no
information. If we start from a well-founded, but undeveloped,
thought, which another has bequeathed to us, we may well hope by
continued reflection to advance farther than the acute man, to
whom we owe the first spark of light.

I therefore first tried whether Hume's objection could not
be put into a general form, and soon found that the concept of
the connection of cause and effect was by no means the only idea
by which the understanding thinks the connection of things a
priori, but rather that metaphysics consists altogether of such
connections. I sought to ascertain their number, and when I had
satisfactorily succeeded in this by starting from a single
principle, I proceeded to the deduction of these concepts, which
I was now certain were not deduced from experience, as Hume had
apprehended, but sprang from the pure understanding. This
deduction (which seemed impossible to my acute predecessor, which
bad never even occurred to any one else, though no one had
hesitated to use the concepts without investigating the basis of
their objective validity) was the most difficult task ever
undertaken in the service of metaphysics; and the worst was that
metaphysics, such as it then existed, could not assist me in the
least, because this deduction alone can render metaphysics
possible. But as soon as I had succeeded in solving Hume's
problem not merely in a particular case, but with respect to the
whole faculty of pure reason, I could proceed safely, though
slowly, to determine the whole sphere of pure reason completely
and from general principles, in its circumference as well as in
its contents. This was required for metaphysics in order to
construct its system according to a reliable method.

But I fear that the execution of Hume's problem in its
widest extent (viz., my Critique of the Pure Reason) will fare as
the problem itself fared, when first proposed. It will be
misjudged because it is misunderstood, and misunderstood because
men choose to skim through the book, and not to think through it-
a disagreeable task, because the work is dry, obscure, opposed to
all ordinary notions, and moreover long-winded. I confess,
however, I did not expect, to hear from philosophers complaints
of want of popularity, entertainment, and facility, when the
existence of a highly prized and indispensable cognition is at
stake, which cannot be established otherwise, than by the
strictest rules of methodic precision. Popularity may follow, but
is inadmissible at the beginning. Yet as regards a certain
obscurity, arising partly from the diffuseness of the plan, owing
to which. the principal points of the investigation are easily
lost sight of, the complaint is just, and I intend to remove it
by the present Prolegomena.

The first-mentioned work, which discusses the pure faculty
of reason in its whole compass and bounds, will remain the
foundation, to which the Prolegomena, as a preliminary, exercise,
refer; for our critique must first be established as a complete
and perfected science, before we can think of letting Metaphysics
appear on the scene, or even have the most distant hope of
attaining it.

We have been long accustomed to seeing antiquated knowledge
produced as new by taking it out of its former context, and
reducing it to system in a new suit of any fancy pattern under
new titles. Most readers will set out by expecting nothing else
from the Critique; but these Prolegomena may persuade him that it
is a perfectly new science, of which no one has ever even
thought, the very idea of which was unknown, and for which
nothing hitherto accomplished can be of the smallest use, except
it be the suggestion of Hume's doubts. Yet even he did not
suspect such a formal science, but ran his ship ashore, for
safety's sake, landing on skepticism, there to let it lie and
rot; whereas my object is rather to give it a pilot, who, by
means of safe astronomical principles drawn from a knowledge of
the globe, and provided with a complete chart and compass, may
steer the ship safely, whither he listeth.

If in a new science, which is wholly isolated and unique in
its kind, we started with the prejudice that we can judge of
things by means of our previously acquired knowledge, which., is
precisely what has first to be called in question, we should only
fancy we saw everywhere what we had already known,. the
expressions, having a similar sound, only that all would appear
utterly metamorphosed, senseless and unintelligible, because we
should have as a foundation out own notions, made by long habit a
second nature, instead of the author's. But the longwindedness of
the work, so far as it depends on the subject, and not the
exposition, its consequent unavoidable dryness and its scholastic
precision are qualities which can only benefit the science,
though they may discredit the book.

Few writers are gifted with the subtlety, and at the same
time with the grace, of David Hume, or with the depth, as well as
the elegance, of Moses Mendelssohn. Yet I flatter myself I might
have made my own exposition popular, had my object been merely to
sketch out a plan and leave its completion to others instead of
having my heart in the welfare of the science, to which I had
devoted myself so long; in truth, it required no little
constancy, and even self-denial, to postpone the sweets of an
immediate success to the prospect of a slower, but more lasting,

Making plans is often the occupation of an opulent and
boastful mind, which thus obtains the reputation of a creative
genius, by demanding what it cannot itself supply; by censuring,
what it cannot improve; and by proposing, what it knows not where
to find. And yet something more should belong to a sound plan of
a general critique of pure reason than mere conjectures, if this
plan is to be other than the usual declamations of pious
aspirations. But pure reason is a sphere so separate and self-
contained, that we cannot touch a part without affecting all the
rest. We can therefore do nothing without first determining the
position; of each part, and its relation to the rest; for, as our
judgment cannot be corrected by anything without, the validity
and use of every part depends upon the relation in which it
stands to all the rest within the domain of reason.

So in the structure of an organized body, the end of each
member can only be deduced from the full conception of the whole.
It may, then, be said of such a critique that it is never
trustworthy except it be perfectly complete, down to the smallest
elements of pure reason. In the sphere of this faculty you can
determine either everything or nothing.

But although a mere sketch, preceding the Critique of Pure
Reason, would be unintelligible, unreliable, and useless, it is
all the more useful as a sequel. For so we are able to grasp the
whole, to examine in detail the chief points of importance in the
science, and to improve in many respects our exposition, as
compared with the first execution of the work.

After the completion of the work I offer here such a plan
which is sketched out after an analytical method, while the work
itself had to be executed in the synthetical style, in order that
the science may present all its articulations, as the structure
of a peculiar cognitive faculty, in their natural combination.
But should any reader find this plan, which I publish as the
Prolegomena to any future Metaphysics, still obscure, let him
consider that not every one is bound to study Metaphysics, that
many minds will succeed very well, in the exact and even in deep
sciences, more closely allied to practical experience,4 while
they cannot succeed in investigations dealing exclusively with
abstract concepts. In such cases men should apply their talents
to other subjects. But he who undertakes to judge, or still more,
to construct, a system of Metaphysics, must satisfy the demands
here made, either by adopting my solution, or by thoroughly
refuting it, and substituting another. To evade it is impossible.

In conclusion, let it be remembered that this much-abused
obscurity (frequently serving as a mere pretext under which
people hide their own indolence or dullness) has its uses, since
all who in other sciences observe a judicious silence, speak
authoritatively in metaphysics and make bold decisions, because
their ignorance is not here contrasted with the knowledge of
others. Yet it does contrast with sound critical principles,
which we may therefore commend in the words of Virgil:

" Ignavum, fucos, pecus a praesepibus arcent. "
"Bees are defending their hives against drones, those
indolent creatures. "

* * * *



Sect. 1: Of the Sources of Metaphysics

If it becomes desirable to formulate any cognition as
science, it will be necessary first to determine accurately those
peculiar features which no other science has in common with it,
constituting its characteristics; otherwise the. boundaries of
all sciences become confused, and none of them can be treated
thoroughly according to its nature.

The characteristics of a science may consist of a simple
difference of object, or of the sources of cognition, or of the
kind of cognition, or perhaps of all three conjointly. On this,
therefore, depends the idea of a possible science and its

First, as concerns the sources of metaphysical cognition,
its very concept implies that they cannot be empirical. Its
principles (including not only its maxims but its basic notions)
must never be derived from experience. It must not be physical
but metaphysical knowledge, viz., knowledge lying beyond
experience. It can therefore have for its basis neither external
experience, which is the source of physics proper, nor internal,
which is the basis of empirical psychology. It is therefore a
priori knowledge, coming from pure Understanding and pure Reason.

But so far Metaphysics would not be distinguishable from
pure Mathematics; it must therefore be called pure philosophical
cognition; and for the meaning of this term I refer to the
Critique of the Pure Reason (II. "Method of Transcendentalism,"
Chap. I., Sec. 1), where the distinction between these two
employments of the reason is sufficiently explained. So far
concerning the sources of metaphysical cognition.

Sect. 2. Concerning the Kind of Cognition which can
alone be called Metaphysical

a. Of the Distinction between Analytical and Synthetical
judgments in general. -- The peculiarity of its sources demands
that metaphysical cognition must consist of nothing but a priori
judgments. But whatever be their origin, or their logical form,
there is a distinction in judgments, as to their content,
according to which they are either merely explicative, adding
nothing to the content of the cognition, or expansive, increasing
the given cognition: the former may be called analytical, the
latter synthetical, judgments.

Analytical judgments express nothing in the predicate but
what has been already actually thought in the concept of the
subject, though not so distinctly or with the same (full)
consciousness. When I say: All bodies are extended, I have not
amplified in the least my concept of body, but have only analyzed
it, as extension was really thought to belong to that concept
before the judgment was made, though it was not expressed, this
judgment is therefore analytical. On the contrary, this judgment,
All bodies have weight, contains in its predicate something not
actually thought in the general concept of the body; it amplifies
my knowledge by adding something to my concept, and must
therefore be called synthetical.

b. The Common Principle of all Analytical Judgments is the
Law of Contradiction. -- All analytical judgments depend wholly
on the law of Contradiction, and are in their nature a priori
cognitions, whether the concepts that supply them with matter be
empirical or not. For the predicate of an affirmative analytical
judgment is already contained in the concept of the subject, of
which it cannot be denied without contradiction. In the same way
its opposite is necessarily denied of the subject in an
analytical, but negative, judgment, by the same law of
contradiction. Such is the nature of the judgments: all bodies
are extended, and no bodies are unextended (i. e., simple).

For this very reason all analytical judgments are a .priori
even when the concepts are empirical, as, for example, Gold is a
yellow metal; for to know this I require no experience beyond my
concept of gold as a yellow metal: it is, in fact, the very
concept, and I need only analyze it, without looking beyond it

c. Synthetical judgments require a different Principle from
the Law of Contradiction.-There are synthetical a posteriori
judgments of empirical origin; but there are also others which
are proved to be certain a priori, and which spring from pure
Understanding and Reason. Yet they both agree in this, that they
cannot possibly spring from the principle of analysis, viz., the
law of contradiction, alone; they require a quite different
principle, though, from whatever they may be deduced, they must
be subject to the law of contradiction, which must never be
violated, even though everything cannot be deduced from it. I
shall first classify synthetical judgments.

1. Empirical judgments are always synthetical. For it would
be absurd to base an analytical judgment on experience, as our
concept suffices for the purpose without requiring any testimony
from experience. That body is extended, is a judgment established
a priori, and not an empirical judgment. For before appealing to
experience, we already have all the conditions of the judgment in
the concept, from which we have but to elicit the predicate
according to the law of contradiction, and thereby to become
conscious of the necessity of the judgment, which experience
could not even teach us.

2. Mathematical judgments are all synthetical. This fact
seems hitherto to have altogether escaped the observation of
those who have analyzed human reason; it even seems directly
opposed to all their conjectures, though incontestably certain,
and most important in its consequences. For as it was found that
the conclusions of mathematicians all proceed according to the
law of contradiction (as is demanded by all apodictic certainty),
men persuaded themselves that the fundamental principles were
known from the same law. This was a great mistake, for a
synthetical proposition can indeed be comprehended according to
the law of contradiction, but only by presupposing another
synthetical proposition from which it follows, but never in

First of all, we must observe that all proper mathematical
judgments are a priori, and not empirical, because they carry
with them necessity, which cannot be obtained from experience.
But if this be not conceded to me, very good; I shall confine my
assertion pure Mathematics, the very notion of which implies that
it contains pure a priori and not empirical cognitions.

It might at first be thought that the proposition 7 + 5 = 12
is a mere analytical judgment, following from the concept of the
sum of seven and five, according to the law of contradiction. But
on closer examination it appears that the concept of the sum Of
7+5 contains merely their union in a single number, without its
being at all thought what the particular number is that unites
them. The concept of twelve is by no means thought by merely
thinking of the combination of seven and five; and analyze this
possible sum as we may, we shall not discover twelve in the
concept. We must go beyond these concepts, by calling to our aid
some concrete image [Anschauung], i.e., either our five fingers,
or five points (as Segner has it in his Arithmetic), and we must
add successively the units of the five, given in some concrete
image [Anschauung], to the concept of seven. Hence our concept is
really amplified by the proposition 7 + 5 = I 2, and we add to
the first a second, not thought in it. Arithmetical judgments are
therefore synthetical, and the more plainly according as we take
larger numbers; for in such cases it is clear that, however
closely we analyze our concepts without calling visual images
(Anscliauung) to our aid, we can never find the sum by such mere

All principles of geometry are no less analytical. That a
straight line is the shortest path between two points, is a
synthetical proposition. For my concept of straight contains
nothing of quantity, but only a quality. The attribute of
shortness is therefore altogether additional, and cannot be
obtained by any analysis of the concept. Here, too, visualization
[Anschauung] must come to aid us. It alone makes the synthesis

Some other principles, assumed by geometers, are indeed
actually analytical, and depend on the law of contradiction; but
they only serve, as identical propositions, as a method of
concatenation, and not as principles, e. g., a=a, the whole is
equal to itself, or a + b > a, the whole is greater than its
part. And yet even these, though they are recognized as valid
from mere concepts, are only admitted in mathematics, because
they can be represented in some visual form [Anschauung]. What
usually makes us believe that the predicate of such apodictic5
judgments is already contained in our concept, and that the
judgment is therefore analytical, is the duplicity of the
expression, requesting us to think a certain predicate as of
necessity implied in the thought of a given concept, which
necessity attaches to the concept. But the question is not what
we are requested to join in thought to the given concept, but
what we actually think together with and in it, though obscurely;
and so it appears that the predicate belongs to these concepts
necessarily indeed, yet not directly but indirectly by an added
visualization [Anschauung].

Sect. 3. A Remark on the General Division of judgments into
Analytical and Synthetical

This division is indispensable, as concerns the Critique of
human understanding, and therefore deserves to be called
classical, though otherwise it is of little use, but this is the
reason why dogmatic philosophers, who always seek the sources of
metaphysical judgments in Metaphysics itself, and not apart from
it, in the pure laws of reason generally, altogether neglected
this apparently obvious distinction. Thus the celebrated Wolf,
and his acute follower Baumgarten, came to seek the proof of the
principle of Sufficient Reason, which is clearly synthetical, in
the principle of Contradiction. In Locke's Essay, however, I find
an indication of my division. For in the fourth book (chap. iii.
Sect. 9, seq.), having discussed the various connections of
representations in judgments, and their sources, one of which he
makes -I identity and contradiction" (analytical judgments), and
another the coexistence of representations in a subject, he
confesses (Sect. 10) that our a priori knowledge of the latter is
very narrow, and almost nothing. But in his remarks on this
species of cognition, there is so little of what is definite, and
reduced to rules, that we cannot wonder if no one, not even Hume,
was led to make investigations concerning this sort of judgments.
For such general and yet definite principles are not easily
learned from other men, who have had them obscurely in their
minds. We must hit on them first by our own reflection, then we
find them elsewhere, where we could not possibly nave found them
at first, because the authors themselves did not know that such
an idea lay at the basis of their observations. Men who never
think independently have nevertheless the acuteness to discover
everything, after it has been once shown them, in what was said
long since, though no one ever saw it there before.

Sect. 4. The General Question of the Prolegemena. - Is
Metaphysics at all Possible?

Were a metaphysics, which could maintain its place as a
science, really in existence; could we say, here is metaphysics,
learn it, and it will convince you irresistibly and irrevocably
of its truth: this question would be useless, and there would
only remain that other question (which would rather be a test of
our acuteness, than a proof of the existence of the thing
itself), "How is the science possible, and how does reason come
to attain it?" But human reason has not been so fortunate in this
case. There is no single book to which you can point as you do to
Euclid, and say: This is Metaphysics; here you may find the
noblest objects of this science, the knowledge of a highest
Being, and of a future existence, proved from principles of pure
reason. We can be shown indeed many judgments, demonstrably
certain, and never questioned; but these are all analytical, and
rather concern the materials and the scaffolding for Metaphysics,
than the extension of knowledge, which is our proper object in
studying it (Sect 2). Even supposing you produce synthetical
judgments (such as the law of Sufficient Reason, which you have
never proved, as you ought to, from pure reason a priori, though
we gladly concede its truth), you lapse when they come to be
employed for your principal object, into such doubtful
assertions, that in all ages one Metaphysics has contradicted
another, either in its assertions, or their proofs, and thus has
itself destroyed its own claim to lasting assent. Nay, the very
attempts to set up such a science are the main cause of the early
appearance of skepticism, a mental attitude in which reason
treats itself with such violence that it could never have arisen
save from complete despair of ever satisfying our most important
aspirations. For long before men began to inquire into nature
methodically, they consulted abstract reason, which had to some
extent been exercised by means of ordinary experience; for reason
is ever present, while laws of nature must usually be discovered
with labor. So Metaphysics floated to the surface, like foam,
which dissolved the moment it was scooped off. But immediately
there appeared a new supply on the surface, to be ever eagerly
gathered up by some, while others, instead of seeking in the
depths the cause of the phenomenon, thought they showed their
wisdom by ridiculing the idle labor of their neighbors.

The essential and distinguishing feature of pure
mathematical cognition among all other a priori cognitions is,
that it cannot at all proceed from concepts, but only by means of
the construction of concepts (see Critique II., Method of
Transcendentalism, Chap. I., sect. 1). As therefore in its
judgments it must proceed beyond the concept to that which its
corresponding visualization [Anschauung] contains, these
judgments neither can, nor ought to, arise analytically, by
dissecting the concept, but are all synthetical.

I cannot refrain from pointing out the disadvantage
resulting to philosophy from the neglect of this easy and
apparently insignificant observation. Hume being prompted (a task
worthy of a philosopher) to cast his eye over the whole field of
a priori cognitions in which human understanding claims such
mighty possessions, heedlessly severed from it a whole, and
indeed its most valuable, province, viz., pure mathematics; for
he thought its nature, or, so to speak, the state-constitution of
this empire, depended on totally different principles, namely, on
the law of contradiction alone; and although he did not divide
judgments in this manner formally and universally as I have done
here, what he said was equivalent to this: that mathematics
contains only analytical, but metaphysics synthetical, a priori
judgments. In this, however, he was greatly mistaken, and the
mistake had a decidedly injurious effect upon his whole
conception. But for this, he would have extended his question
concerning the origin of our synthetical judgments far beyond the
metaphysical concept of Causality, and included in it the
possibility of mathematics a priori also, for this latter he must
have assumed to be equally synthetical. And then he could not
have based his metaphysical judgments on mere experience without
subjecting the axioms of mathematics equally to experience, a
thing which he was far too acute to do. The good company into
which metaphysics would thus have been brought, would have saved
it from the danger of a contemptuous ill-treatment, for the
thrust intended for it must have reached mathematics, which was
not and could not have been Hume's intention. Thus that acute man
would have been led into considerations which must needs be
similar to those that now occupy us, but which would have gained
inestimably by his inimitably elegant style.

Metaphysical judgments, properly so called, are all
synthetical. We must distinguish judgments pertaining to
metaphysics from metaphysical judgments properly so called. Many
of the former are analytical, but they only afford the means for
metaphysical judgments, which are the whole end of the science,
and which are always synthetical. For if there be concepts
pertaining to metaphysics (as, for example, that of substance),
the judgments springing from simple analysis of them also pertain
to metaphysics, as, for example, substance is that which only
exists as subject; and by means of several such analytical
judgments, we seek to approach the definition of the concept. But
as the analysis of a pure concept of the understanding pertaining
to metaphysics, does not proceed in any different manner from the
dissection of any other, even empirical, concepts, not pertaining
to metaphysics (such as: air is an elastic fluid, the elasticity
of which is not destroyed by any known degree of cold), it
follows that the concept indeed, but not the analytical judgment,
is properly metaphysical. This science has something peculiar in
the production of its a priori cognitions, which must therefore
be distinguished from the features it has in common with other
rational knowledge. Thus the judgment, that all the substance in
things is permanent, is a synthetical and properly metaphysical

If the a priori principles, which constitute the materials
of metaphysics, have first been collected according to fixed
principles, then their analysis will be of great value; it might
be taught as a particular part (as a philosophia definitiva),
containing nothing but analytical judgments pertaining to
metaphysics, and could be treated separately from the synthetical
which constitute metaphysics proper. For indeed these analyses
are not elsewhere of much value, except in metaphysics, i.e., as
regards the synthetical judgments, which are to be generated by
these previously analyzed concepts.

The conclusion drawn in this section then is, that
metaphysics is properly concerned with synthetical propositions a
priori, and these alone constitute its end, for which it indeed
requires various dissections of its concepts, viz., of its
analytical judgments, but wherein the procedure is not different
from that in every other kind of knowledge, in which we merely
seek to render our concepts distinct by analysis. But the
generation of a priori cognition by concrete images as well as by
concepts, in fine of synthetical propositions a priori in
philosophical cognition, constitutes the essential subject of

Weary therefore as well of dogmatism, which teaches us
nothing, as of skepticism, which does not even promise us
anything, not even the quiet state of a contented ignorance;
disquieted by the importance of knowledge so much needed; and
lastly, rendered suspicious by long experience of all knowledge
which we believe we possess, or which offers itself, under the
title of pure reason: there remains but one critical question on
the answer to which our future procedure depends, viz., Is
Metaphysics at all possible? But this question must be answered
not by skeptical objections to the asseverations of some actual
system of metaphysics (for we do not as yet admit such a thing to
exist), but from the conception, as yet only problematical, of a
science of this sort.

In the Critique of Pure Reason I have treated this question
synthetically, by making inquiries into pure reason itself, and
endeavoring in this source to determine the elements as well as
the laws of its pure use according to principles. The task is
difficult, and requires a resolute reader to penetrate by degrees
into a system, based on no data except reason itself, and which
therefore seeks, without resting upon any fact, to unfold
knowledge from its original germs. Prolegomena, however, are
designed for preparatory exercises; they are intended rather to
point out what we have to do in order if possible to actualize a
science, than to propound it. They must therefore rest upon
something already known as trustworthy, from which we can set out
with confidence, and ascend to sources as yet unknown, the
discovery of which will not only explain to us what we knew, but
exhibit a sphere of many cognitions which all spring from the
same sources. The method of Prolegomena, especially of those
designed as a preparation for future metaphysics, is consequently

But it happens fortunately, that though we cannot assume
metaphysics to be an actual science, we can say with confidence
that certain pure a priori synthetical cognitions, pure
Mathematics and pure Physics are actual and given; for both
contain propositions, which are thoroughly recognized as
apodictically certain, partly by mere reason, partly by general
consent arising from experience, and yet as independent of
experience. We have therefore some at least uncontested
synthetical knowledge a priori, and need not ask whether it be
possible, for it is actual, but how it is possible, in order that
we may deduce from the principle which makes the given cognitions
possible the possibility of all the rest.

Sect. 5. The General Problem: How is Cognition from Pure Reason

We have above learned the significant distinction between
analytical and synthetical judgments. The possibility of
analytical propositions was easily comprehended, being entirely
founded on the law of Contradiction. The possibility of
synthetical a posteriori judgments, of those which are gathered
from experience, also requires no particular explanation; for
experience is nothing but a continual synthesis of perceptions.
There remain therefore only synthetical propositions a priori, of
which the possibility must be sought or investigated, because
they must depend upon other principles than the law of

But here we need not first establish the possibility of such
propositions so as to ask whether they are possible. For there
are enough of them which indeed are of undoubted certainty, and
as our present method is analytical, we shall start from the
fact, that such synthetical but purely rational cognition
actually exists; but we must now inquire into the reason of this
possibility, and ask, how such cognition is possible, in order
that we may from the principles of its possibility be enabled to
determine the conditions of its use, its sphere and its limits.
The proper problem upon which all depends, when expressed with
scholastic precision, is therefore: How are Synthethetic
Propositions a priori possible?

For the sake of popularity I have above expressed this
problem somewhat differently, as an inquiry into purely rational
cognition, which I could do for once without detriment to the
desired comprehension, because, as we have only to do here with
metaphysics and its sources, the reader will, I hope, after the
foregoing remarks, keep in mind that when we speak of purely
rational cognition, we do not mean analytical, but synthetical

Metaphysics stands or falls with the solution of this
problem: its very existence depends upon it. Let any one make
metaphysical assertions with ever so much plausibility, let him
overwhelm us with conclusions, if he has not previously proved
able to answer this question satisfactorily, I have a right to
say this is all vain baseless philosophy and false wisdom. You
speak through pure reason, and claim, as it were to create
cognitions a priori. by not only dissecting given concepts, but
also by asserting connections which do not rest upon the law of
contradiction, and which you believe you conceive quite
independently of all experience; how do you arrive at this, and
how will you justify your pretensions? An appeal to the consent
of the common sense of mankind cannot be allowed; for that is a
witness whose authority depends merely upon rumor. Says Horace:

" Quodcunque ostendis mihi sic, incredulus odi."
"To all that which thou provest me thus, I refuse to give
credence. "

The answer to this question, though indispensable, is
difficult; and though the principal reason that it was not made
long ago is, that the possibility of the question never occurred
to anybody, there is yet another reason, which is this that a
satisfactory answer to this one question requires a much more
persistent, profound, and painstaking reflection, than the most
diffuse work on Metaphysics, which on its first appearance
promised immortality to its author. And every intelligent reader,
when he carefully reflects what this problem requires, must at
first be struck with its difficulty, and would regard it as
insoluble and even impossible, did there not actually exist pure
synthetical cognitions a priori. This actually happened to David
Hume, though he did not conceive the question in its entire
universality as is done here, and as must be done, should the
answer be decisive for all Metaphysics. For how is it possible,
says that acute man, that when a concept is given me, I can go
beyond it and connect with it another, which is not contained in
it, in such a manner as if the latter necessarily belonged to the
former? Nothing but experience can furnish us with such
connections (thus he concluded from the difficulty which he took
to be an impossibility), and all that vaunted necessity, or, what
is the same thing, all cognition assumed to be a priori, is
nothing but a long habit of accepting something as true, and
hence of mistaking subjective necessity for objective.

Should my reader complain of the difficulty and the trouble
which I occasion him in the solution of this problem, he is at
liberty to solve it himself in an easier way. Perhaps he will
then feel under obligation to the person who has undertaken for
him a labor of so profound research, and will rather be surprised
at the facility with which, considering the nature of the
subject, the solution has been attained. Yet it has cost years of
work to solve the problem in its whole universality (using the
term in the mathematical sense, viz., for that which is
sufficient for all cases), and finally to exhibit it in the
analytical form, as the reader finds it here.

All metaphysicians are therefore solemnly and legally
suspended from their occupations till they shall have answered in
a satisfactory manner the question, "How are synthetic cognitions
a priori possible?" For the answer contains the only credentials
which they must show when they have anything to offer in the name
of pure reason. But if they do not possess these credentials,
they can expect nothing else of reasonable people, who have been
deceived so often, than to be dismissed without further ado.

If they on the other hand desire to carry on their business,
not as a science, but as an art of wholesome oratory suited to
the common sense of man, they cannot in justice be prevented.
They will then speak the modest language of a rational belief,
they will grant that they are not allowed even to conjecture, far
less to know, anything which lies beyond the bounds of all
possible experience, but only to assume (not for speculative use,
which they must abandon, but for practical purposes only) the
existence of something that is possible and even indispensable
for the guidance of the understanding and of the will in life. In
this mariner alone can they be called useful and wise men, and
the more so as they renounce the title of metaphysicians; for the
latter profess to be speculative philosophers, and since, when
judgments a prior: are under discussion, poor probabilities
cannot be admitted (for what is declared to be known a priori is
thereby announced as necessary), such men cannot be permitted to
play with conjectures, but their assertions must be either
science, or are worth nothing at all.

It may be said, that the entire transcendental philosophy,
which necessarily precedes all metaphysics, is nothing but the
complete solution of the problem here propounded, in systematical
order and completeness, and hitherto we have never had any
transcendental philosophy; for what goes by its name is properly
a part of metaphysics, whereas the former sciences intended first
to constitute the possibility of the 'matter, and must therefore
precede all metaphysics. And it is not surprising that when a
whole science, deprived of all help from other sciences, and
consequently in itself quite new, is required to answer a -single
question satisfactorily, we should find the answer troublesome
and difficult, nay even shrouded in obscurity.

As we now proceed to this solution according to the
analytical method, in which we assume that such cognitions from
pure reasons actually exist, we can only appeal to two sciences
of theoretical cognition . which alone is under consideration
here), pure mathematics and pure natural science (physics). For
these alone can exhibit to us objects in a definite and
actualizable form (in der Anschauung), and consequently (if there
should occur in them a cognition a priori) can show the truth or
conformity of the cognition to the object in concrete, that is,
its actuality, from which we could proceed to the reason of its
possibility by the analytic method. This facilitates our work
greatly for here universal considerations are not only applied to
facts, but even start from them, while in a synthetic procedure
they must strictly be derived in abstracts from concepts.

But, in order to rise from these actual and at the same time
well-grounded pure cognitions a priori to such a possible
cognition of the same as we are seeking, viz., to metaphysics as
a science, we must comprehend that which occasions it, I mean the
mere natural, though in spite of its truth not unsuspected,
cognition a priori which lies at the bottom of that science, the
elaboration of which without any critical investigation of its
possibility is commonly called metaphysics. In a word, we must
comprehend the natural conditions of such a science as a part of
our inquiry, and thus the transcendental problem will be
gradually answered by a division into four questions:

1. How is pure mathematics possible?
2. How is pure natural science possible?
3. How is metaphysics in general possible?
4. How is metaphysics as a science possible?

It may be seen that the solution of these problems, though
chiefly designed to exhibit the essential matter of the Critique,
has yet something peculiar, which for itself alone deserves
attention. This is the search for the sources of given sciences
in reason itself, so that its faculty of knowing something a
priori may by its own deeds be investigated and measured. By this
procedure these sciences gain, if not with regard to their
contents, yet as to their proper use, and while they throw light
on the higher question concerning their common origin, they give,
at the same time, an occasion better to explain their own nature.

* * * *


Here is a great and established branch of knowledge,
encompassing even now a wonderfully large domain and promising an
unlimited extension in the future. Yet it carries with it
thoroughly apodictical certainty, i.e., absolute necessity, which
therefore rests upon no empirical grounds. Consequently it is a
pure product of reason, and moreover is thoroughly synthetical.
[Here the question arises:] "How then is it possible for human
reason to produce a cognition of this nature entirely a priori?"

Does not this faculty [which produces mathematics], as it
neither is nor can be based upon experience, presuppose some
ground of cognition a priori, which lies deeply hidden, b,.--,
which might reveal itself by these its effects, if their first
beginnings were but diligently ferreted out?

Sect. 7. But we find that all mathematical cognition has
this peculiarity: it must first exhibit its concept in a visual
form [Anschauung] and indeed a priori, therefore in a visual form
which is not empirical, but pure. Without this mathematics cannot
take a single step; hence its judgments are always visual, viz.,
"Intuitive"; whereas philosophy must be satisfied with discursive
judgments from mere concepts, and though it may illustrate its
doctrines through a visual figure, can never derive them from it.
This observation on the nature of mathematics gives us a clue to
the first and highest condition of its possibility, which is,
that some non-sensuous visualization [called pure intuition, or
reine Anschauung] must form its basis, in which all its concepts
can be exhibited or constructed, in concrete and yet a priori. If
we can find out this pure intuition and its possibility, we may
thence easily explain how synthetical propositions a priori are
possible in pure mathematics, and consequently how this science
itself is possible. Empirical intuition [viz., sense-perception]
enables us without difficulty to enlarge the concept which we
frame of an object of intuition [or sense-perception], by new
predicates, which intuition [i.e., sense-perception] itself
presents synthetically in experience. Pure intuition [viz., the
visualization of forms in our imagination, from which every thing
sensual, i.e., every thought of material qualities, is excluded]
does so likewise, only with this difference, that in the latter
case the synthetical judgment is a priori certain and
apodictical, in the former, only a posteriori and empirically
certain; because this latter contains only that which occurs in
contingent empirical intuition, but the former, that which must
necessarily be discovered in pure intuition. He.-e intuition,
being an intuition a priori, is before all experience, viz.,
before any perception of particular objects, inseparably
conjoined with its concept.

Sect. 8. But with this step our perplexity seems rather to
increase than to lessen. For the question now is, "How is it
possible to intuit [in a visual form] anything a priori" An
intuition [viz., a visual sense perception] is such a
representation as immediately depends upon the presence of the
object. Hence it seems impossible to intuit from the outset a
priori, because intuition would in that event take place without
either a former or a present object to refer to, and by
consequence could not be intuition. Concepts indeed are such,
that we can easily form some of them a priori, viz., such as
contain nothing but the thought of an object in general; and we
need not find ourselves in an immediate relation to the object.
Take, for instance, the concepts of Quantity, of Cause, etc. But
even these require, in order to make them understood, a certain
concrete use-that is, an application to some sense-experience
[Anschauung], by which an object of them is given us. But how can
the intuition of the object [its visualization] precede the
object itself?

Sect. 9. If our intuition [i.e., our sense-experience] were
perforce of such a nature as to represent things as they are in
themselves, there would not be any intuition a priori, but
intuition would be always empirical. For I can only know what is
contained in the object in itself when it is present and given to
me. It is indeed even then incomprehensible how the visualizing
[Anschauung] of a present thing should make me know this thing as
it is in itself, as its properties cannot migrate into my faculty
of representation. But even granting this possibility, a
visualizing of that sort would not take place a priori, that is,
before the object were presented to me; for without this latter
fact no reason of a relation between my representation and the
object can be imagined, unless it depend upon a direct

Therefore in one way only can my intuition [Anschauung]
anticipate the actuality of the object, and be a cognition a
priori, viz.: if my intuition contains nothing but the form of
sensibility, antedating in my subjectivity all the actual
impressions through which I am affected by objects.

For that objects of sense can only be intuitd according to
this form of sensibility I can know a priori. Hence it follows:
that propositions, which concern this form of sensuous intuition
only, are possible and valid for objects of the senses; as also,
conversely, that intuitions which are possible a priori can never
concern any other things than objects of our senses.7

Sect. 10. Accordingly, it is only the form of sensuous
intuition by which we can intuit things a priori, but by which we
can know objects only as they appear to us (to our senses), not
as they are in themselves; and this assumption is absolutely
necessary if synthetical propositions a priori be granted as
possible, or if, in case they actually occur, their possibility
is to be comprehended and determined beforehand.

Now, the intuitions which pure mathematics lays at the
foundation of all its cognitions and judgments which appear at
once apodictic and necessary are Space and Time. For mathematics
must first have all its concepts in intuition, and pure
mathematics in pure intuition, that is, it must construct them.
If it proceeded in any other way, it would be impossible to make
any headway, for mathematics proceeds, not analytically by
dissection of concepts, but synthetically, and if pure intuition
be wanting, there is nothing in which the matter for synthetical
judgments a priori can be given. Geometry is based upon the pure
intuition of space. Arithmetic accomplishes its concept of number
by the successive addition of units in time; and pure mechanics
especially cannot attain its concepts of motion without employing
the representation of time. Both representations, however, are
only intuitions; for if we omit from the empirical intuitions of
bodies and their alterations (motion) everything empirical, or
belonging to sensation, space and time still remain, which are
therefore pure intuitions that lie a priori at the basis of the
empirical. Hence they can never be omitted, but at the same time,
by their being pure intuitions a priori, they prove that they are
mere forms of our sensibility, which must precede all empirical
intuition, or perception of actual objects, and conformably to
which objects can be known a priori, but only as they appear to

Sect. 11. The problem of the present section is therefore
solved. Pure mathematics, as synthetical cognition a priori, is
only possible by referring to no other objects than those of the
senses. At the basis of their empirical intuition lies a pure
intuition (of space and of time) which is a priori. This is
possible, because the latter intuition is nothing but the mere
form of sensibility, which precedes the actual appearance of the
objects, in, that it, in fact, makes them possible. Yet this
faculty of intuiting a priori affects not the matter of the
phenomenon (that is, the sense-element in it, for this
constitutes that which is empirical), but its form, viz., space
and time. Should any man venture to doubt that these are
determinations adhering not to things in themselves, but to their
relation to our sensibility, I should be glad to know how it can
be possible to know the constitution of things a priori, viz.,
before we have any acquaintance with them and before they are
presented to us. Such, however, is the case with space and time.
But this is quite comprehensible as soon as both count for
nothing more than formal conditions of our sensibility, while the
objects count merely as phenomena; for then the form of the
phenomenon, i.e., pure intuition, can by all means be represented
as proceeding from ourselves, that is, a priori.

Sect. 12. In order to add something by way of illustration
and confirmation, we need only watch the ordinary and necessary
procedure of geometers. All proofs of the complete congruence of
two given figures (where the one can in every respect be
substituted for the other) come ultimately to this that they may
be made to coincide; which is evidently nothing else than a
synthetical proposition resting upon immediate intuition, and
this intuition must be pure, or given a priori, otherwise the
proposition could not rank as apodictically certain, but would
have empirical certainty only. In that case, it could only be
said that it is always found to be so, and holds good only as far
as our perception reaches. That everywhere space (which (in its
entirety] is itself no longer the boundary of another space) has
three dimensions, and that space cannot in any way have more, is
based on the proposition that not more than three lines can
intersect at right angles in one point; but this proposition
cannot by any means be shown from concepts, but rests immediately
on intuition, and indeed on pure and a priori intuition, because
it is apodictically certain. That we can require a line to be
drawn to infinity (in indefinitum), or that a series of changes
(for example, spaces traversed by motion) shall be infinitely
continued, presupposes a representation of space and time, which
can only attach to intuition, namely, so far as it in itself is
bounded by nothing, for from concepts it could never be inferred.
Consequently, the basis of mathematics actually are pure
intuitions, which make its synthetical and apodictically valid
propositions possible. Hence our transcendental deduction of the
notions of space and of time explains at the same time the
possibility of pure mathematics. Without some such deduction its
truth may be granted, but its existence could by no means be
understood, and we must assume II that everything which can be
given to our senses (to the external senses in space, to the
internal one in time) is intuitd by us as it appears to us, not
as it is in itself."

Sect. 13. Those who cannot yet rid themselves of the notion
that space and time are actual qualities inhering in things in
themselves, may exercise their acumen on the following paradox.
When they have in vain attempted its solution, and are free from
prejudices at least for a few moments, they will suspect that the
degradation of space and of time to mere forms of @ur sensuous
intuition may perhaps be well founded,

If two things are quite equal in all respects ask much as
can be ascertained by all means possible, quantitatively and
qualitatively, it must follow, that the one can in all cases and
under all circumstances replace the other, and this substitution
would not occasion the least perceptible difference. This in fact
is true of plane figures in geometry; but some spherical figures
exhibit, notwithstanding a complete internal agreement, such a
contrast in their external relation, that the one figure cannot
possibly be put in the place of the other. For instance, two
spherical triangles on opposite hemispheres, which have an arc of
the equator as their common base, may be quite equal, both as
regards sides and angles, so that nothing is to be found in
either, if it be described for itself alone and completed, that
would not equally be applicable to both; and yet the one cannot
be put in the place of the other (being situated upon the
opposite hemisphere). Here then is an internal difference between
the two triangles, which difference our understanding cannot
describe as internal, and which only manifests itself by external
relations in space.

But I shall adduce examples, taken from common life, that
are more obvious still.

What can be more similar in every respect and in every part
more alike to my hand and to my ear, than their images in a
mirror? And yet I cannot put such a hand as is seen in the glass
in the place of its archetype; for if this is a right hand, that
in the glass is a left one, and the image or reflection of the
right ear is a left one which never can serve as a substitute for
the other. There are in this case no internal differences which
our understanding could determine by thinking alone. Yet the
differences are internal as the senses teach, for,
notwithstanding their complete equality and similarity, the left
hand cannot be enclosed in the same bounds as the right one (they
are not congruent); the glove of one hand cannot be used for the
other. What is the solution? These objects are not
representations of things as they are in themselves, and as the
pure understanding would know them, but sensuous intuitions, that
is, appearances, the possibility of which rests upon the relation
of certain things unknown in themselves to something else, viz.,
to our sensibility. Space is the form of the external intuition
of this sensibility, and the internal determination of every
space is only possible by the determination of its external
relation to the whole space, of which it is a part (in other
words, by its relation to the external sense). That is to say,
the part is only possible through the whole, which is never the
case with things in themselves, as objects of the mere
understanding, but with appearances only. Hence the difference
between similar and equal things, which are yet not congruent
(for instance, two symmetric helices), cannot be made
intelligible by any concept, but only by the relation to the
right and the left hands which immediately refers to intuition.


Pure Mathematics, and especially pure geometry, can only
have objective reality on condition that they refer to objects of
sense. But in regard to the latter the principle holds good, that
our sense representation is not a representation of things in
themselves but of the way in which they appear to us. Hence it
follows, that the propositions of geometry are not the results of
a mere creation of our poetic imagination, and that therefore
they cannot be referred with assurance to actual objects; but
rather that they are necessarily valid of space, and consequently
of all that may be found in space, because space is nothing else
than the form of all external appearances, and it is this form
alone in which objects of sense can be given. Sensibility, the
form of which is the basis of geometry, is that upon which the
possibility of external appearance depends. Therefore these
appearances can never contain anything but what geometry
prescribes to them.

It would be quite otherwise if the senses were so
constituted as to represent objects as they are in themselves.
For then it would not by any means follow from the conception of
space, which with all its properties serves to the geometer as an
a priori foundation, together with what is thence inferred, must
be so in nature. The space of the geometer would be considered a
mere fiction, and it would not be credited with objective
validity, because we cannot see how things must of necessity
agree with an image of them, which we make spontaneously and
previous to our acquaintance with them. But if this image, or
rather this formal intuition, is the essential property of our
sensibility, by means of which alone objects are given to us, and
if this sensibility represents not things in themselves, but
their appearances: we shall easily comprehend, and at the same
time indisputably prove, that all external objects of our world
of sense must necessarily coincide in the most rigorous way with
the propositions of geometry; because sensibility by means of its
form of external intuition, viz., by space, the same with which
the geometer is occupied, makes those objects at all possible as
mere appearances.

It will always remain a remarkable phenomenon in the history
of philosophy, that there was a time, when even mathematicians,
who at the same time were philosophers, began to doubt, not of
the accuracy of their geometrical propositions so far as they
concerned space, but of their objective validity and the
applicability of this concept itself, and of all its corollaries,
to nature. They showed much concern whether a-line in nature
might not consist of physical points, and consequently that true
space in the object might consist of simple [discrete] parts,
while the space which the geometer has in his mind [being
continuous] cannot be such. They did not recognize that this
mental space renders possible the physical space, i.e., the
extension of matter; that this pure space is not at all a quality
of things in themselves, but a form of our sensuous faculty of
representation; and that all objects in space are mere
appearances, i.e., not things in themselves but representations
of our sensuous intuition. But such is the case, for the space of
the geometer is exactly the form of sensuous intuition which we
find a priori in us, and contains the ground of the possibility
of all external appearances (according to their form), and the
latter must necessarily and most rigidly agree with the
propositions of the geometer, which he draws not from any
fictitious concept, but from the subjective basis of all external
phenomena, which is sensibility itself. In this and no other way
can geometry be made secure as to the undoubted objective reality
of its propositions against all the intrigues of a shallow
Metaphysics, which is surprised at them [the geometrical
propositions], because it has not traced them to the sources of
their concepts.


Whatever is given us as object, must be given us in
intuition. All our intuition however takes place by means of the
senses only; the understanding intuits nothing, but only
reflects. And as we have just shown that the senses never and in
no manner enable us to know things in themselves, but only their
appearances, which are mere representations of the sensibility,
we conclude that all bodies, together with the space in which
they are, must be considered nothing but mere representations in
us, and exist nowhere but in our thoughts.' You will say: Is not
this manifest idealism?

Idealism consists in the assertion, that there are none but
thinking beings, all other things, which we think are perceived
in intuition, being nothing but representations in the thinking
beings, to which no object external to them corresponds in fact.
Whereas I say, that things as objects of our senses existing
outside us are given, but we know nothing of what they may be in
themselves, knowing only their appearances, 1. e., the
representations which they cause in us by affecting our senses.
Consequently I grant by all means that there are bodies without
us, that is, things which, though quite unknown to us as to what
they are in themselves, we yet know by the representations which
their influence on our sensibility procures us, and which we call
bodies, a term signifying merely the appearance of the thing
which is unknown to us, but not therefore less actual. Can this
be termed idealism? It is the very contrary.

Long before Locke's time, but assuredly since him, it has
been generally assumed and granted without detriment to the
actual existence of external things, that many of their
predicates may be said to belong not to the things in themselves,
but to their appearances, and to have no proper existence outside
our representation. Heat, color, and taste, for instance, are of
this kind. Now, if I go farther, and for weighty reasons rank as
mere appearances the remaining qualities of bodies also, which
are called primary, such as extension, place, and in general
space, with all that which belongs to it (impenetrability or
materiality, space, etc.)-no one in the least can adduce the
reason of its being inadmissible. As little as the man who admits
colors not to be properties of the object in itself, but only as
modifications of the sense of sight, should on that account be
called an idealist, so little can my system be named idealistic,
merely because I find that more, nay, A11 the properties which
constitute the intuition of a body belong merely to its

The existence of the thing that appears is thereby not
destroyed, as in genuine idealism, but it is only shown, that we
cannot possibly know it by the senses as it is in itself.

I should be glad to know what my assertions must be in order
to avoid all idealism. Undoubtedly, I should say, that the
representation of space is not only perfectly conformable to the
relation which our sensibility has to objects-that I have said-
but that it is quite similar to the object,-an assertion in which
I can find as little meaning as if I said that the sensation of
red has a similarity to the property of vermilion, which in me
excites this sensation.


Hence we may at once dismiss an easily foreseen but futile
objection, "that by admitting the ideality of space and of time
the whole sensible world would be turned into mere sham." At
first all philosophical insight into the nature of sensuous
cognition was spoiled, by making the sensibility merely a
confused mode of representation, according to which we still know
things as they are, but without being able to reduce everything
in this our representation to a clear consciousness; whereas
proof is offered by us that sensibility consists, not in this
logical distinction of clearness and obscurity, but in the
genetical one of the origin of cognition itself. For sensuous
perception represents things not at all as they are, but only the
mode in which they affect our senses, and consequently by
sensuous perception appearances only and not things themselves
are given to the understanding for reflection. After this
necessary corrective, an objection rises from an unpardonable and
almost intentional misconception, as if my doctrine turned all
the things of the world of sense into mere illusion.

When an appearance is given us, we are still quite free as
to how we should judge the matter. The appearance depends upon
the senses, but the judgment upon the understanding, and the only
question is, whether in the determination of the object there is
truth or not. But the difference between truth and dreaming is
not ascertained by the nature of the representations, which are
referred to objects (for they are the same in both cases), but by
their connection according to those rules, which determine the
coherence of the representations in the concept of an object, and
by ascertaining whether they can subsist together in experience
or not. And it is not the fault of the appearances if our
cognition takes illusion for truth, i.e., if the intuition, by
which an object is given us, is considered a concept of the thing
or of its existence also, which the understanding can only think.
The senses represent to us the paths of the planets as now
progressive, now retrogressive, and herein is neither falsehood
nor truth, because as long as we hold this path to be nothing but
appearance, we do not judge of the objective nature of their
motion. But as a false judgment may easily arise when the
understanding is not on its guard against this subjective mode of
representation being considered objective, we say they appear to
move backward; it is not the senses however which must be charged
with the illusion, but the understanding, whose province alone it
is to give an objective judgment on appearances.

Thus, even if we did not at all reflect on the origin of our
representations, whenever we connect our intuitions of sense
(whatever they may contain), in space and in time, according to
the rules of the coherence of all cognition in experience,
illusion or truth will arise according as we are negligent or
careful. It is merely a question of the use of sensuous
representations in the understanding, and not of their origin. In
the same way, if I consider all the representations of the
senses, together with their form, space and time, to be nothing
but appearances, and space and time to be a mere form of the
sensibility, which is not to be met with in objects out of it,
and if I make use of these representations in reference to
possible experience only, there is nothing in my regarding them
as appearances that can lead astray or cause illusion. For all
that they can correctly cohere according to rules of truth in
experience. Thus all the propositions of geometry hold good of
space as well as of all the objects of the senses, consequently
of all possible experience, whether I consider space as a mere
form of the sensibility, or as something cleaving to the things
themselves. In the former case however I comprehend how I can
know a priori these propositions concerning all the objects of
external intuition. Otherwise, everything else as regards all
possible experience remains just as if I had not departed from
the vulgar view.

But if I venture to go beyond all possible experience with
my notions of space and time, which I cannot refrain from doing
if I proclaim them qualities inherent in things in themselves
(for what should prevent me from letting them hold good of the
same things, even though my senses might be different, and
unsuited to them?), then a grave error may arise due to illusion,
for thus I would proclaim to be universally valid what is merely
a subjective condition of the intuition of things and sure only
for all objects of sense, viz., for all possible experience; I
would refer this condition to things in themselves, and do not
limit it to the conditions of experience.

My doctrine of the ideality of space and of time, therefore,
far from reducing the whole sensible world to mere illusion, is
the only means of securing the application of one of the most
important cognitions (that which mathematics propounds a priori)
to actual objects, and of preventing its being regarded as mere
illusion. For without this observation it would be quite
impossible to make out whether the intuitions of space and time,
which we borrow from no experience, and which yet lie in our
representation a priori, are not mere phantasms of our brain, to
which objects do not correspond, at least not adequately, and
consequently, whether we have been able to show its
unquestionable validity with regard to all the objects of the
sensible world just because they are mere appearances.

Secondly, though these my principles make appearances of the
representations of the senses, they are so far from turning the
truth of experience into mere illusion, that they are rather the
only means of preventing the transcendental illusion, by which
metaphysics has hitherto been deceived, leading to the childish
endeavor of catching at bubbles, because appearances, which are
mere representations, were taken for things in themselves. Here
originated the remarkable event of the antimony of Reason which I
shall mention by and by, and which is destroyed by the single
observation, that appearance, as long as it is employed in
experience, produces truth, but the moment it transgresses the
bounds of experience, and consequently becomes transcendent,
produces nothing but illusion.

Inasmuch therefore, as I leave to things as we obtain them
by the senses their actuality, and only limit our sensuous
intuition of these things to this, that they represent in no
respect, not even in the pure intuitions of space and of time,
anything more than mere appearance of those thin-s, but never
their constitution in themselves, this is not a sweeping illusion
invented for nature by me. My protestation too against all
charges of idealism is so valid and clear as even to seem
superfluous, were there not incompetent judges, who, while they
would have an old name for every deviation from their perverse
though common opinion, and never judge of the spirit of
philosophic nomenclature, but cling to the letter only, are ready
to put their own conceits in the place of well-defined notions,
and thereby deform and distort them. I have myself given this my
theory the name of transcendental idealism, but that cannot
authorize any one to confound it either with the empirical
idealism of Descartes, (indeed, his was only an insoluble
problem, owing to which he thought every one at liberty to deny
the existence of the corporeal world, because it could never be
proved satisfactorily), or with the mystical and visionary
idealism of Berkeley, against which and other similar phantasms
our Critique contains the proper antidote. My idealism concerns
not the existence of things (the doubting of which, however,
constitutes idealism in the ordinary sense), since it never came
into my head to doubt it, but it concerns the sensuous
representation of things, to which space and time especially
belong. Of these [viz., space and time], consequently of all
appearances in general, I have only shown, that they are neither
things (but mere modes of representation), nor determinations
belonging to things in themselves. But the word "transcendental,"
which with me means a reference of our cognition, i.e., not to
things, but only to the cognitive faculty, was meant to obviate
this misconception. Yet rather than give further occasion to it
by this word, I now retract it, and desire this idealism of mine
to be called critical. But if it be really an objectionable
idealism to convert actual thin.-Is (not appearances) into mere
representations.. by what name shall we call him who conversely
changes mere representations to things? It may, I think, be
called "dreaming idealism," in contradistinction to the former,
which may be called "visionary," both of which are to be refuted
by my transcendental, or, better, critical idealism.

* * * *


Sect. 14. Nature is the existence of things, so far as it is
determined according to universal laws. Should nature signify the
existence of things in themselves, we could never know it either
a priori or a posteriori. Not a priori, for how can we know what
belongs to things in themselves, since this never can be done by
the dissection of our concepts (in analytical judgments)? We do
not want to know what is contained in our concept of a thing (for
the [concept describes what] belongs to its logical being), but
what is in the actuality of the thing superadded to our concept,
and by what the thing itself is determined in its existence
outside the concept. Our understanding, and the conditions on
which alone it can connect the determinations of things in their
existence, do not prescribe any rule to things themselves; these
do not conform to our understanding, but it must conform itself
to them; they must therefore be first given us in order to gather
these determinations from them, wherefore they would not be known
a priori.

A cognition of the nature of things in themselves a
posteriori would be equally impossible. For, if experience is to
teach us laws, to which the existence of things is subject, these
laws, if they regard things in themselves, must belong to them of
necessity even outside our experience. But experience teaches us
what exists and how it exists, but never that it must necessarily
exist so and not otherwise. Experience therefore can never teach
us the nature of things in themselves.

Sect. 15. We nevertheless actually possess a pure science of
nature in which are propounded, a priori and with all the
necessity requisite to apodictical propositions, laws to which
nature is subject. I need only call to witness that propaedeutic
of natural science which, under the title of the universal
Science of Nature, precedes all Physics (which is founded upon
empirical principles). In it we have Mathematics applied to
appearance, and also merely discursive principles (or those
derived from concepts), which constitute the philosophical part
of the pure cognition of nature. But there are several things in
it, which are not quite pure and independent of empirical
sources: such as the concept of motion, that of impenetrability
(upon which the empirical concept of matter rests), that of
inertia, and many others, which prevent its being called a
perfectly pure science of nature. Besides, it only refers to
objects of the external sense and therefore does not give an
example of a universal science of nature, in the strict sense,
for such a science must reduce nature in general, whether it
regards the object of the external or that of the internal sense
(the object of Physics as well as Psychology), to universal laws.
But among the principles of this universal physics there are a
few which actually have the required universality; for instance,
the propositions that "substance is permanent, " and that "every
event is determined by a cause according to constant laws," etc.
These are actually universal laws of nature, which subsist
completely a priori. There is then in fact a pure science of
nature, and the question arises, How is it possible?

Sect. 16. The word "nature" assumes yet another meaning,
which determines the object, whereas in the former sense it only
denotes the conformity to law [Gesetzmdssigkeit] of the
determinations of the existence of things generally. If we
consider it materialiter (i.e., in the matter that forms its
objects) "nature is the complex of all the objects of
experience." And with this only are we now concerned, for
besides, things which can never be objects of experience, if they
must be known as to their nature, would oblige us to have
recourse to concepts whose meaning could never be given in
concrete (by any example of possible experience). Consequently we
must form for ourselves a list of concepts of their nature, the
reality whereof (i.e., whether they actually refer to objects, or
are mere creations of thought) could never be determined. The
cognition of what cannot be an object of experience would be
hyperphysical, and with things hyperphysical we are here not
concerned, but only with the cognition of nature, the actuality
of which can be confirmed by experience, though it [the cognition
of nature] is possible a priori and precedes all experience.

Sect. 17. The formal [aspect] of nature in this narrower
sense is therefore the conformity to law of all the objects of
experience, and so far as it is known a priori, their necessary
conformity. But it has just been shown that the laws of nature
can never be known a priori in objects so far as they are
considered not in reference to possible experience, but as things
in themselves. And our inquiry here extends not to things in
themselves (the properties of which we pass by), but to things as
objects of possible experience, and the complex of these is what
we properly designate as nature. And now I ask, when the
possibility of a cognition of nature a priori is in question,
whether it is better to arrange the problem thus: How can we know
a priori that things as objects of experience necessarily conform
to law? or thus: How is it possible to know a priori the
necessary conformity to law of experience itself as regards all
its objects generally?

Closely considered, the solution of the problem, represented
in either way, amounts, with regard to the pure cognition of
nature (which is the point of the question at issue), entirely to
the same thing. For the subjective laws, under which alone an
empirical cognition of things is possible, hold good of these
things, as objects of possible experience (not as things in
themselves, which are not considered here). Either of the
following statements means quite the same: "A judgment of
observation can never rank as experience, without the law, that
'whenever an event is observed, it is always referred to some
antecedent, which it follows according to a universal rule'";
alternatively, "Everything, of which experience teaches that it
happens, must have a cause."

It is, however, more commendable to choose the first
formula. For we can a priori and previous to all given objects
have a cognition of those conditions, on which alone experience
is possible, but never of the laws to which things may in
themselves be subject, without reference to possible experience.
We cannot therefore study the nature of things a priori otherwise
than by investigating the conditions and the universal (though
subjective) laws, under which alone such a cognition as
experience (as to mere form) is possible, and we determine
accordingly the possibility of things, as objects of experience.
For if I should choose the second formula, and seek the
conditions a priori, on which nature as an object of experience
is possible, I might easily fall into error, and fancy that I was
speaking of nature as a thing in itself, and then move round in
endless circles, in a vain search for laws concerning things of
which nothing is given me.

Accordingly we shall here be concerned with experience only,
and the universal conditions of its possibility which are given a
priori. Thence we shall determine nature as the whole object of
all possible experience. I think it will be understood that I
here do not mean the rules of the observation of a nature that is
already given, for these already presuppose experience. I do not
mean how (through experience) we can study the laws of nature;
for these would not then be laws a priori, and would yield us no
pure science of nature; but [I mean to ask] how the condi. tions
a priori of the possibility of experience are at the same time
the sources from which all the universal laws of nature must be

Sect. 18. In the first place we must state that, while all
judgments of experience [Erfahrungsurtheile] are empirical (i.e.,
have their ground in immediate senseperception), vice versa, all
empirical judgments [empirische Urtheile] are not judgments of
experience, but, besides the empirical, and in general besides
what is given to the sensuous intuition, particular concepts must
yet be superadded-concepts which have their origin quite a priori
in the pure understanding, and under which every perception must
be first of all subsumed and then by their means changed into

Empirical judgments, so far as they have objective validity,
are judgments of experience; but those which are only
subjectively valid, I name mere judgments of perception. The
latter require no pure concept of the understanding, but only the
logical connection of perception in a thinking subject. But the
former always require, besides the representation of the sensuous
intuition, particular concepts originally begotten in the
understanding, which produce the objective validity of the
judgment of experience.

All our judgments are at first merely judgments of
perception; they hold good only for us (i.e., for our subject),
and we do not till afterwards give them a new reference (to an
object), and desire that they shall always hold good for us and
in the same way for everybody else; for when a judgment agrees
with an object, all judgments concerning the same object must
likewise agree among themselves, and thus the objective validity
of the judgment of experience signifies nothing else than its
necessary universality of application. And conversely when we
have reason to consider a judgment necessarily universal (which
never depends upon perception, but upon the pure concept of the
understanding, under which the perception is subsumed), we must
consider it objective also, that is, that it expresses not merely
a reference of our perception to a subject, but a quality of the
object. For there would be no reason for the judgments of other
men necessarily agreeing with mine, if it were not the unity of
the object to which they all refer, and with which they accord;
hence they must all agree with one another.

Sect. 19. Therefore objective validity and necessary
universality (for everybody) are equivalent terms, and though we
do not know the object in itself, yet when we consider a judgment
as universal, and also necessary, we understand it to have
objective validity. By this judgment we know the object (though
it remains unknown as it is in itself) by the universal and
necessary connection of the given perceptions. As this is the
case with all objects of sense, judgments of experience take
their objective validity not from the immediate cognition of the
object (which is impossible), but from the condition of universal
validity in empirical judgments, which, as already said, never
rests upon empirical, or, in short, sensuous conditions, but upon
a pure concept of the understanding. The object always remains
unknown in itself; but when by the concept of the understanding
the connection of the representations of the object, which are
given to our sensibility, is determined as universally valid, the
object is determined by this relation, and it is the judgment
that is objective.

To illustrate the matter: When we say, "the room is warm,
sugar sweet, and wormwood bitter,"9 -- we have only subjectively
valid judgments, I do not at all expect that I or any other
person shall always find it as I now do; each of these sentences
only expresses a relation of two sensations to the same subject,
to myself, and that only in my present state of perception;
consequently they are not valid of the object. Such are judgments
of perception. judgments of experience are of quite a different
nature. What experience teaches me under certain circumstances,
it must always teach me and everybody; and its validity is not
limited to the subject nor to its state at a particular time.
Hence I pronounce all such judgments as being objectively valid.
For instance, when I say the air is elastic, this judgment is as
yet a judgment of perception only-I do nothing but refer two of
my sensations to one another. But, if I would have it called a
judgment of experience, I require this connection to stand under
a condition, which makes it universally valid. I desire therefore
that I and everybody else should always connect necessarily the
same perceptions under the same circumstances.

Sect. 20. We must consequently analyze experience in order
to see what is contained in this product of the senses and of the
understanding, and how the judgment of experience itself is
possible. The foundation is the intuition of which I become
conscious, i.e., perception (perceptio), which pertains merely to
the senses. But in the next place, there are acts of judging
(which belong only to the understanding). But this judging may be
twofold-first, I may merely compare perceptions and connect them
in a particular state of my consciousness; or, secondly, I may
connect them in consciousness generally. The former judgment is
merely a judgment of perception, and of subjective validity only:
it is merely a connection of perceptions in my mental state,
without reference to the object. Hence it is not, as is commonly
imagined, enough for experience to compare perceptions and to
connect them in consciousness through judgment; there arises no
universality and necessity, for which alone judgments can become
objectively valid and be called experience.

Quite another judgment therefore is required before
perception can become experience. The given intuition must be
subsumed under a concept, which determines the form of judging in
general relatively to the intuition, connects its empirical
consciousness in consciousness generally, and thereby procures
universal validity for empirical judgments. A concept of this
nature is a pure a priori concept of the Understanding, which
does nothing but determine for an intuition the general way in
which it can be used for judgments. Let the concept be that of
cause, then it determined the intuition which is subsumed under
it, e.g., that of air, relative to judgments in general, viz.,
the concept of air serves with regard to its expansion in the
relation of antecedent to consequent in a hypothetical judgment.
The concept of cause accordingly is a pure concept of the
understanding, which is totally disparate from all possible
perception, and only serves to determine the representation
subsumed under it, relatively to judgments in general, and so to
make a universally valid judgment possible.

Before, therefore, a judgment of perception can become a
judgment of experience, it is requisite that the perception
should be subsumed under some such a concept of the
understanding.; for instance, air ranks under the concept of
causes, which determines our judgment about it in regard to its
expansion as hypothetical.10 Thereby the expansion of the air is
represented not as merely belonging to the perception of the air
in my present state or in several states of mine, or in the state
of perception of others, but as belonging to it necessarily. The
judgment, "the air is elastic," becomes universally valid, and a
judgment of experience, only by certain judgments preceding it,
which subsume the intuition of air under the concept of cause and
effect: and they thereby determine the perceptions not merely as
regards one another in me, but relatively to the form of judging
in general, which is here hypothetical, and in this way they
render the empirical judgment universally valid.

If all our synthetical judgments are analyzed so far as they
are objectively valid, it will be found that they never consist
of mere intuitions connected only (as is commonly believed) by
comparison into a judgment; but that they would be impossible
were not a pure concept of the understanding superadded to the
concepts abstracted from intuition, under which concept these
latter are subsumed, and in this manner only combined into an
objectively valid judgment. Even the judgments of pure
mathematics in their simplest axioms are not exempt from this
condition. The principle, II a straight line is the shortest
between two points," presupposes that the line is subsumed under
the concept of quantity, which certainly is no mere intuition,
but bas its seat in the understanding alone, and serves to
determine the intuition (of the line) with regard to the
judgments which may be made about it, relatively to their
quantity, that is, to plurality (as judicia plurativa).11 For
under them it is understood that in a given intuition there is
contained a plurality of homogenous parts.

Sect. 21. To prove, then, the possibility of experience so
far as it rests upon pure concepts of the understanding a priori,
we must first represent what belongs to judgments in general and
the various functions of the understanding, in a complete table.
For the pure concepts of the understanding must run parallel to
these functions, as such concepts are nothing more than concepts
of intuitions in general, so far as these are determined by one
or other of these functions of judging, in themselves, that is,
necessarily and universally. Hereby also the a priori principles
of the possibility of all experience, as of an objectively valid
empirical cognition, will be precisely determined. For they are
nothing but propositions by which all perception is (under
certain universal conditions of intuition) subsumed under those
pure concepts of the understanding.


1. As to Quantity.

2. As to Quality.

3. As to Relation.

4. As to Modality.


1 . As to Quantity.
Unity (the Measure).
Plurality (the Quantity).
Totality (the Whole).

2. As to Quality.

3. As to Relation.

4. As to Modality.


1. Axioms of Intuition.
2. Anticipations of Perception.
3. Analogies of Experience.
4. Postulates of Empirical Thinking generally.

Sect. 21a. In order to comprise the whole matter in one
idea, it is first necessary to remind the reader that we are
discussing not the origin of experience, but of that which lies
in experience. The former pertains to empirical psychology, and
would even then never be adequately explained without the latter,
which belongs to the Critique of cognition, and particularly of
the understanding.

Experience consists of intuitions, which belong to the
sensibility, and of judgments, which are entirely a work of the
understanding. But the judgments, which the understanding forms
alone from sensuous intuitions, are far from being judgments of
experience. For in the one case the judgment connects only the
perceptions as they are given in the sensuous intuition, while in
the other the judgments must express what experience in general,
and not what the mere perception (which possesses only subjective
validity) contains. The judgment of experience must therefore add
to the sensuous intuition and its logical connection in a
judgment (after it has been rendered universal by comparison)
something that determines the synthetical judgment as necessary
and therefore as universally valid. This can be nothing else than
that concept which represents the intuition as determined in
itself with regard to one form of judgment rather than another,
viz., a concept of that synthetical unity of intuitions which can
only be represented by a given logical function of judgments.

Sect. 22. The sum of the matter is this: the business of the
senses is to intuit -- that of the understanding is to think. But
thinking is uniting representations in one consciousness. This
union originates either merely relative to the subject, and is
accidental and subjective, or is absolute, and is necessary or
objective. The union of representations in one consciousness is
judgment. Thinking therefore is the same as judging, or referring
representations to judgments in general. Hence judgments are
either merely subjective, when representations are referred to a
consciousness in one subject only, and united in it, or
objective, when they are united in a consciousness generally,
that is, necessarily. The logical functions of all judgments are
but various modes of uniting representations in consciousness.
But if they serve for concepts, they are concepts of their
necessary union in a consciousness, and so principles of
objectively valid judgments. This union in a consciousness is
either analytical, by identity, or synthetical, by the
combination and addition of various representations one to
another. Experience consists in the synthetical connection of
phenomena (perceptions) in consciousness, so far as this
connection is necessary. Hence the pure concepts of the
understanding are those under which all perceptions must be
subsumed ere they can serve for judgments of experience, in which
the synthetical unity of the perceptions is represented as
necessary and universally valid.12

Sect. 23. judgments, when considered merely as the condition
of the union of given representations in a consciousness, are
rules. These rules, so far as they represent the union as
necessary, are rules a priori, and so far as they cannot be
deduced from higher rules, are fundamental principles. But in
regard to the possibility of all experience, merely in relation
to the form of thinking in it, no conditions of judgments of
experience are higher than those which bring the phenomena,
according to the various form of their intuition, under pure
concepts of the understanding, and render the empirical judgment
objectively valid. These concepts are therefore the a priori
principles of possible experience.

The principles of possible experience are then at the same
time universal laws of nature, which can be known a priori. And
thus the problem in our second question, "How is the pure Science
of Nature possible?" is solved. For the system which is required
for the form of a science is to be met with in perfection here,
because, beyond the above-mentioned formal conditions of all
judgments in general offered in logic, no others are possible,
and these constitute a logical system. The concepts grounded
thereupon, which contain the a priori conditions of all
synthetical and necessary judgments, accordingly constitute a
transcendental system. Finally the principles, by means of which
all phenomena are subsumed under these concepts, constitute a
physical13 system, that is, a system of nature, which precedes
all empirical cognition of nature, makes it even possible, and
hence may in strictness be denominated the universal and pure
science of nature.

Sect. 24. The first one14 of the physiological principles
subsumes all phenomena, as intuitions in space and time, under
the concept of Quantity, and is so far a principle of the
application of Mathematics to experience. The second one subsumes
the empirical element, viz., sensation, which denotes the real in
intuitions, not indeed directly under the concept of quantity,
because sensation is not an intuition that contains either space
or time, though it places the respective object into both. But
still there is between reality (sense-representation) and the
zero, or total void of intuition in time, a difference which has
a quantity. For between every given degree of light and of
darkness, between every degree of beat and of absolute cold,
between every degree of weight and of absolute lightness, between
every degree of occupied space and of totally void space,
diminishing degrees can be conceived, in the same manner as
between consciousness and total unconsciousness (the darkness of
a psychological blank) ever diminishing degrees obtain. Hence
there is no perception that can prove an absolute absence of it;
for instance, no psychological darkness that cannot be considered
as a kind of consciousness, which is only out-balanced by a
stronger consciousness. This occurs in all cases of sensation,
and so the understanding can anticipate even sensations, which
constitute the peculiar quality of empirical representations
(appearances), by means of the principle: "that they all have
(consequently that what is real in all phenomena has) a degree."
Here is the second application of mathematics (mathesis
intensortim) to the science of nature.

Sect. 25. Anent the relation of appearances merely with a
view to their existence, the determination is not mathematical
but dynamical, and can never be objectively valid, consequently
never fit for experience, if it does not come under a priori
principles by which the cognition of experience relative to
appearances becomes even possible. Hence appearances must be
subsumed under the concept of Substance, which is the foundation
of all determination of existence, as a concept of the thing
itself; or secondly so far as a succession is found among
phenomena, that is, an event-under the concept of an Effect with
reference to Cause; or lastly-so far as coexistence is to be
known objectively, that is, by a judgment of experience-under the
concept of Community (action and reaction).15 Thus a priori
principles form the basis of objectively valid, though empirical
judgments, that is, of the possibility of experience so far as it
must connect objects as existing in nature. These principles are
the proper laws of nature, which may be termed dynamical.

Finally the cognition of the agreement and connection not
only of appearances among themselves in experience, but of their
relation to experience in general, belongs to the judgments of
experience. This relation contains either their agreement with
the formal conditions, which the understanding knows, or their
coherence with the materials of the senses and of perception, or
combines both into one concept. Consequently it contains
Possibility, Actuality, and Necessity according to universal laws
of nature; and this constitutes the physical doctrine of method,
or the distinction of truth and of hypotheses, and the bounds of
the certainty of the latter.

Sect. 26. The third table of Principles drawn from the
nature of the understanding itself after the critical method,
shows an inherent perfection, which raises it far above every
other table which has hitherto though in vain been tried or may
yet be tried by analyzing the objects themselves dogmatically. It
exhibits all synthetical a priori principles completely and
according to one principle, viz., the faculty of judging in
general, constituting the essence of experience as regards the
understanding, so that we can be certain that there are no more
such principles, which affords a satisfaction such as can never
be attained by the dogmatical method. Yet is this not all: there
is a still greater merit in it.

We must carefully bear in mind the proof which shows the
possibility of this cognition a priori, and at the same time
limits all such principles to a condition which must never be
lost sight of, if we desire it not to be misunderstood, and
extended in use beyond the original sense which the understanding
attaches to it. This limit is that they contain nothing but the
conditions of possible experience in general so far as it is
Subjected to laws a priori. Consequently I do not say, that
things in themselves possess a quantity, that their actuality
possesses a degree, their existence a connection of accidents in
a substance, etc. This nobody can prove, because such a
synthetical connection from mere concepts, without any reference
to sensuous intuition on the one side, or connection of it in a
possible experience on the other, is absolutely impossible. The
essential limitation of the concepts in these principles then is:
That all things stand necessarily a priori under the
aforementioned conditions, as objects of experience only.

Hence there follows secondly a specifically peculiar mode of
proof of these principles: they are not directly referred to
appearances and to their relations, but to the possibility of
experience, of which appearances constitute the matter only, not
the form. Thus they are referred to objectively and universally
valid synthetical propositions, in which we distinguish judgments
of experience from those of perception. This takes place because
appearances, as mere intuitions, occupying a part of space and
time, come under the concept of Quantity, which unites their
multiplicity a priori according to rules synthetically. Again, so
far as the perception contains, besides intuition, sensibility,
and between the latter and nothing (i.e., the total disappearance
of sensibility), there is an ever-decreasing transition, it is
apparent that that which is in appearances must have a degree, so
far as it (viz., the perception) does not itself occupy any part
of space or of time.16 Still the transition to actuality from
empty time or empty space is only possible in time; consequently
though sensibility, as the quality of empirical intuition, can
never be known a priori, by its specific difference from other
sensibilities, yet it can, in a possible experience in general,
as a quantity of perception be intensely distinguished from every
other similar perception. Hence the application of mathematics to
nature, as regards the sensuous intuition by which nature is
given to us, becomes possible and is thus determined.

Above all, the reader must pay attention to the mode of
proof of the principles which occur under the title of Analogies
of experience. For these do not refer to the genesis of
intuitions, as do the principles of applied mathematics, but to
the connection of their existence in experience; and this can be
nothing but the determination of their existence in time
according to necessary laws, under which alone the connection is
objectively valid, and thus becomes experience. The proof
therefore does not turn on the synthetical unity in the
connection of things in themselves, but merely of perceptions,
and of these not in regard to their matter, but to the
determination of time and of the relation of their existence in
it, according to universal laws. If the empirical determination
in relative time is indeed objectively valid (i.e., experience),
these universal laws contain the necessary determination of
existence in time generally (viz., according to a rule of the
understanding a priori).

In these Prolegomena I cannot further descant on the
subject, but my reader (who has probably been long accustomed to
consider experience a mere empirical synthesis of perceptions,
and hence not considered that it goes much beyond them, as it
imparts to empirical judgments universal validity, and for that
purpose requires a pure and a priori unity of the understanding)
is recommended to pay special attention to this distinction of
experience from a mere aggregate of perceptions, and to judge the
mode of proof from this point of view.

Sect. 27. Now we are prepared to remove Hume's doubt. He
justly maintains, that we cannot comprehend by reason the
possibility of Causality, that is, of the reference of the
existence of one thing to the existence of another, which is
necessitated by the former. I add, that we comprehend just as
little the concept of Subsistence, that is, the necessity that at
the foundation of the existence of things there lies a subject
which cannot itself be a predicate of any other thing; nay, we
cannot even form a notion of the possibility of such a thing
(though we can point out examples of its use in experience). The
very same incomprehensibility affects the Community of things, as
we cannot comprehend bow from the state of one thing an inference
to the state of quite another thing beyond it, and vice versa,
can be drawn, and how substances which have each their own
separate existence should depend upon one another necessarily.
But I am very far from holding these concepts to be derived
merely from experience, and the necessity represented in them, to
be imaginary and a mere illusion produced in us by long habit. On
the contrary, I have amply shown, that they and the theorems
derived from them are firmly established a priori, or before all
experience, and have their undoubted objective value, though only
with regard to experience.

Sect. 28. Though I have no notion of such a connection of
things in themselves, that they can either exist as substances,
or act as causes, or stand in community with others (as parts of
a real whole), and I can just as little conceive such properties
in appearances as such (because those concepts contain nothing
that lies in the appearances, but only what the understanding
alone must think): we have yet a notion of such a connection of
representations in our understanding, and in judgments generally;
consisting in this that representations appear in one sort of
judgments as subject in relation to predicates, in another as
reason in relation to consequences, and in a third as parts,
which constitute together a total possible cognition. Besides we
know a priori that without considering the representation of an
object as determined in some of these respects, we can have no
valid cognition of the object, and, if we should occupy ourselves
about the object in itself, there is no possible attribute, by
which I could know that it is determined under any of these
aspects, that is, under the concept either of substance, or of
cause, or (in relation to other substances) of community, for I
have no notion of the possibility of such a connection of
existence. But the question is not how things in themselves, but
how the empirical cognition of things is determined as regards
the above aspects of judgments in general, that is, how things,
as objects of experience, can and shall be subsumed under these
concepts of the understanding. And then it is clear, that I
completely comprehend not only the possibility, but also the
necessity of subsuming all phenomena under these concepts, that
is, of using them for principles of the possibility of

Sect. 29. When making an experiment with Hume's
problematical concept (his crux metaphysicorum), the concept of
cause, we have, in the first place, given a priori, by means of
logic, the form of a conditional judgment in general, i.e., we
have one given cognition as antecedent and another as
consequence. But it is possible, that in perception we may meet
with a rule of relation, which runs thus: that a certain
phenomenon is constantly followed by another (though not
conversely), and this is a case for me to use the hypothetical
judgment, and, for instance, to say, if the sun shines long
enough upon a body, it grows warm. Here there is indeed as yet no
necessity of connection, or concept of cause. But I proceed and
say, that if this proposition, which is merely a subjective
connection of perceptions, is to be a judgment of experience, it
must be considered as necessary and universally valid. Such a
proposition would be, II the sun is by its light the cause of
heat." The empirical rule is now considered as a law, and as
valid not merely of appearances but valid of them for the
purposes of a possible experience which requires universal and
therefore necessarily valid rules. I therefore easily comprehend
the concept of cause, as a concept necessarily belonging to the
mere form of experience, and its possibility as a synthetical
union of perceptions in consciousness generally; but I do not at
all comprehend the possibility of a thing generally as a cause,
because the concept of cause denotes a condition not at all
belonging to things, but to experience. It is nothing in fact but
an objectively valid cognition of appearances and of their
succession, so far as the antecedent can be conjoined with the
consequent according to the rule of hypothetical judgments.

Sect. 30. Hence if the pure concepts of the understanding do
not refer to objects of experience but to things in themselves
(noumena), they have no signification whatever. They serve, as it
were, only to decipher appearances, that we may be able to read
them as experience. The principles which arise from their
reference to the sensible world, only serve our understanding for
empirical use. Beyond this they are arbitrary combinations,
without objective reality, and we can neither know their
possibility a priori, nor verify their reference to objects, let
alone make it intelligible by any example; because examples can
only be borrowed from some possible experience, consequently the
objects of these concepts can be found nowhere but in a possible

This complete (though to its originator unexpected) solution
of Hume's problem rescues for the pure concepts of the
understanding their a priori origin, and for the universal laws
of nature their validity, as laws of the understanding, yet in
such a way as to limit their use to experience, because their
possibility depends solely on the reference of the understanding
to experience, but with a completely reversed mode of connection
which never occurred to Hume, not by deriving them from
experience, but by deriving experience from them.

This is therefore the result of all our foregoing inquiries:
"All synthetical principles a priori are nothing more than
principles of possible experience, and can never be referred to
things in themselves, but to appearances as objects of
experience. And hence pure mathematics as well as a pure science
of nature can never be referred to anything more than mere
appearances, and can only represent either that which makes
experience generally possible, or else that which, as it is
derived from these principles, must always be capable of being
represented in some possible experience."

Sect. 31. And thus we have at last something definite, upon
which to depend in all metaphysical enterprises, which have
hitherto, boldly enough but always at random, attempted
everything without discrimination. That the aim of their
exertions should be so near, struck neither the dogmatical
thinkers nor those who, confident in their supposed sound common
sense, started with concepts and principles of pure reason (which
were legitimate and natural, but destined for mere empirical use)
in quest of fields of knowledge, to which they neither knew nor
could know any determinate bounds, because they bad never
reflected nor were able to reflect on the nature or even on the
possibility of such a pure understanding.

Many a naturalist of pure reason (by which I mean the man
who believes he can decide in matters of metaphysics without any
science) may pretend, that lie long ago by the prophetic spirit
of his sound sense, not only suspected, but knew and
comprehended, what is here propounded with so much ado, or, if he
likes, with prolix and pedantic pomp: "that with all our reason
we can never reach beyond the field of experience." But when he
is questioned about his rational principles individually, he must
grant, that there are many of them which be has not taken from
experience, and which are therefore independent of it and valid a
priori. How then and on what grounds will he restrain both
himself and the dogmatist, who makes use of these concepts and
principles beyond all possible experience, because they are
recognized to be independent of it? And even he, this adept in
sound sense, in spite of all his assumed and cheaply acquired
wisdom, is not exempt from wandering inadvertently beyond objects
of experience into the field of chimeras. He is often deeply
enough involved in them, though in announcing everything as mere
probability, rational conjecture, or analogy, be gives by his
popular language a color to his groundless pretensions.

Sect. 32. Since the oldest days of philosophy inquirers into
pure reason have conceived, besides the things of sense, or
appearances (phenomena), which make up the sensible world,
certain creations of the understanding (Verstandeswesen), called
noumena, which should constitute an intelligible world. And as
appearance and illusion were by those men identified (a thing
which we may well excuse in an undeveloped epoch), actuality was
only conceded to the creations of thought.

And we indeed, rightly considering objects of sense as mere
appearances, confess thereby that they are based upon a thing in
itself, though we know not this thing in its internal
constitution, but only know its appearances, viz., the way in
which our senses are affected by this unknown something. The
understanding therefore, by assuming appearances, grants the
existence of things in themselves also, and so far we may say,
that the representation of such things as form the basis of
phenomena, consequently of mere creations of the understanding,
is not only admissible, but unavoidable.

Our critical deduction by no means excludes things of that
sort (noumena), but rather limits the principles of the Aesthetic
(the science of the sensibility) to this, that they shall not
extend to all things, as everything would then be turned into
mere appearance, but that they shall only hold good of objects of
possible experience. Hereby then objects of the understanding are
granted, but with the inculcation of this rule which admits of no
exception: "that we neither know nor can know anything at all
definite of these pure objects of the understanding, because our
pure concepts of the understanding as well as our pure intuitions
extend to nothing but objects of possible experience,
consequently to mere things of sense, and as soon as we leave
this sphere these concepts retain no meaning whatever."

Sect. 33. There is indeed something seductive in our pure
concepts of the understanding, which tempts us to a transcendent
use, -- a use which transcends all possible experience. Not only
are our concepts of substance, of power, of action, of reality,
and others, quite independent of experience, containing nothing
of sense appearance, and so apparently applicable to things in
themselves (noumena), but, what strengthens this conjecture, they
contain a necessity of determination in themselves, which
experience never attains. The concept of cause implies a rule,
according to which one state follows another necessarily; but
experience can only show us, that one state of things often, or
at most, commonly, follows another, an(i therefore affords
neither strict universality, nor necessity.

Hence the Categories seem to have a deeper meaning and
import than can be exhausted by their empirical use, and so the
understanding inadvertently adds for itself to the house of
experience a much more extensive wing, which it fills with
nothing but creatures of thought, without ever observing that it
has transgressed with its otherwise lawful concepts the bounds of
their use.

Sect. 34. Two important, and even indispensable, though very
dry, investigations had therefore become indispensable in the
Critique of Pure Reason,-viz., the two chapters "Vom Schematismus
der reinen Verstandsbegriffe," and "Vom Grunde der Unterscheidung
aller Verstandesbegriffe uberhaupt in Phenomena und Noumena. " In
the former it is shown, that the senses furnish not the pure
concepts of the understanding in concreto, but only the schedule
for their use, and that the object conformable to it occurs only
in experience (as the product of the understanding from materials
of the sensibility). In the latter it is shown, that, although
our pure concepts of the understanding and our principles are
independent of experience, and despite of the apparently greater
sphere of their use, still nothing whatever can be thought by
them beyond the field of experience, because they can do nothing
but merely determine the logical form of the judgment relatively
to given intuitions. But as there is no intuition at all beyond
the field of the sensibility, these pure concepts, as they cannot
possibly be exhibited in concrete, are void of all meaning;
consequently all these noumena, together with their complex, the
intelligible world,17 are nothing but representation of a
problem, of which the object in itself is possible, but the
solution, from the nature of our understanding, totally
impossible. For our understanding is not a faculty of intuition,
but of the connection of given intuitions in experience.
Experience must therefore contain all the objects for our
concepts; but beyond it no concepts have any significance, as
there is no intuition that might offer them a foundation.

Sect. 35. The imagination may perhaps be forgiven for
occasional vagaries, and for not keeping carefully within the
limits of experience, since it gains life and vigor by such
flights, and since it is always easier to moderate its boldness,
than to stimulate its languor. But the understanding which ought
to think can never be forgiven for indulging in vagaries; for we
depend upon it alone for assistance to set bounds, when
necessary, to the vagaries of the imagination.

But the understanding begins its aberrations very innocently
and modestly. It first elucidates the elementary cognitions,
which inhere in it prior to all experience, but yet must always
have their application in experience. It gradually drops these
limits, and what is there to prevent it, as it has quite freely
derived its principles from itself? And then it proceeds first to
newly-imagined powers in nature, then to beings outside nature;
in short to a world, for whose construction the materials cannot
be wanting, because fertile fiction furnishes them abundantly,
and though not confirmed, is never refuted, by experience. This
is the reason that young thinkers arc so partial to nietaph3,sics
of the truly dogmatical kind, and often sacrifice to it their
time and their talents, which might be otherwise better employed.

But there is no use in trying to moderate these fruitless
endeavors of pure reason by all manner of cautions as to the
difficulties of solving questions so occult, by complaints of the
limits of our reason, and by degrading our assertions into mere
conjectures. For if their impossibility is not distinctly shown,
and reason's cognition of its own essence does not become a true
science, in which the field of its right use is distinguished, so
to say, with mathematical certainty from that of its worthless
and idle use, these fruitless efforts will never be abandoned for

Sect. 36. How is Nature itself possible?

This question -- the highest point that transcendental
philosophy can ever reach, and to which, as its boundary and
completion, it must proceed-properly contains two questions.

First: How is nature at all possible in the material sense,
by intuition, considered as the totality of appearances; how are
space, time, and that which fills both -- the object of
sensation, in general possible? The answer is: By means of the
constitution of our Sensibility, according to which it is
specifically affected by objects, which are in themselves unknown
to it, and totally distinct from those phenomena. This answer is
given in the Critique itself in the transcendental Aesthetic, and
in these Prolegomena by the solution of the first general

Secondly: How is nature possible in the formal sense, as the
totality of the rules, under which all phenomena must come, in
order to be thought as connected in experience? The answer must
be this: it is only possible by means of the constitution of our
Understanding, according to which all the above representations
of the sensibility are necessarily referred to a consciousness,
and by which the peculiar way in which we think (viz., by rules),
and hence experience also, are possible, but must be clearly
distinguished from an insight into the objects in themselves.
This answer is given in the Critique itself in the transcendental
Logic, and in these Prolegomena, in the course of the solution of
the second main problem.

But how this peculiar property of our sensibility itself is
possible, or that of our understanding and of the apperception
which is necessarily its basis and that of all thinking, cannot
be further analyzed or answered, because it is of them that we
are in need for all our answers and for all our thinking about

There are many laws of nature, which we can only know by
means of experience; but conformity to law in the connection of
appearances, i.e., in nature in general, we cannot discover by
any experience, because experience itself requires laws which are
a priori at the basis of its possibility.

The possibility of experience in general is therefore at the
same time the universal law of nature, and the principles of the
experience are the very laws of nature. For we do not know nature
but as the totality of appearances, i.e., of representations in
us, and hence we can only derive the laws of its connection from
the principles of their connection in us, that is, from the
conditions of their necessary union in consciousness, which
constitutes the possibility of experience.

Even the main proposition expounded throughout this section
-- that universal laws of nature can be distinctly known a priori
-- leads naturally to the proposition: that the highest
legislation of nature must lie in ourselves, i.e., in our
understanding, and that we must not seek the universal laws of
nature in nature by means of experience, but conversely must seek
nature, as to its universal conformity to law, in the conditions
of the possibility of experience, which lie in our sensibility
and in our understanding. For bow were it otherwise possible to
know a priori these laws, as they are not rules of analytical
cognition, but truly synthetical extensions of it?

Such a necessary agreement of the principles of possible
experience with the laws of the possibility of nature, can only
proceed from one of two reasons: either these laws are drawn from
nature by means of experience, or conversely nature is derived
from the laws of the possibility of experience in general, and is
quite the same as the mere universal conformity to law of the
latter. The former is self-contradictory, for the universal laws
of nature can and must be known a priori (that is, independent of
all experience), and be the foundation of all empirical use of
the understanding; the latter alternative therefore alone

But we must distinguish the empirical laws of nature, which
always presuppose particular perceptions, from the pure or
universal laws of nature, which, without being based on
particular perceptions, contain merely the conditions of their
necessary union in experience. In relation to the latter, nature
and possible experience are quite the same, and as the conformity
to law here depends upon the -necessary connection of appearances
in experience (without which we cannot know any object whatever
in the sensible world), consequently upon the original laws of
the understanding, it seems at first strange, but is not the less
certain, to say: The understanding does not derive its laws (a
priori) from, but prescribes them to, nature.

Sect. 37. We shall illustrate this seemingly bold
proposition by an example, which will show, that laws, which we
discover in objects of sensuous intuition (especially when these
laws are known as necessary), are commonly held by us to be such
as have been placed there by the understanding, in spite of their
being similar in all points to the laws of nature, which we
ascribe to experience.

Sect. 38. If we consider the properties of the circle, by
which this figure combines so many arbitrary determinations of
space in itself, at once in a universal rule, we cannot avoid
attributing a constitution (eine Natur) to this geometrical
thing. Two right lines, for example, which intersect one another
and the circle, howsoever they may be drawn, are always divided
so that the rectangle constructed with the segments of the one is
equal to that constructed with the segments of the other. The
question now is: Does this law lie in the circle or in the
understanding, that is, Does this figure, independently of the
understanding, contain in itself the ground of the law, or does
the understanding, having constructed according to its concepts
(according to the quality of the radii) the figure itself,
introduce into it this law of the chords cutting one another in
geometrical proportion? When we follow the proofs of this law, we
soon perceive, that it can only be derived from the condition on
which the understanding founds the construction of this figure,
and which is that of the equality of the radii. But, if we
enlarge this concept, to pursue further the unity of various
properties of geometrical figures under common laws, and consider
the circle as a conic section, which of course is subject to the
same fundamental conditions of construction as other conic
sections, we shall find that all the chords which intersect
within the ellipse, parabola, and hyperbola, always intersect so
that the rectangles of their segments are not indeed equal, but
always bear a constant ratio to one another. If we proceed still
farther, to the fundamental laws of physical astronomy, we find a
physical law of reciprocal attraction diffused over all material
nature, the rule of which is: II that it decreases inversely as
the square of the distance from each attracting point, i.e., as
the spherical surfaces increase, over which this force spreads,"
which law seems to be necessarily inherent in the very nature of
things, and hence is usually propounded as knowable a priori.
Simple as the sources of this law are, merely resting upon the
relation of spherical surfaces of different radii, its
consequences are so valuable with regard to the variety of their
agreement and its regularity, that not only are all possible
orbits of the celestial bodies conic sections, but such a
relation of these orbits to each other results, that no other law
of attraction, than that of the inverse square of the distance,
can be imagined as fit for a cosmical system.

Here accordingly is a nature that rests upon laws which the
understanding knows a priori, and chiefly from the universal
principles of the determination of space. Now I ask: Do the laws
of nature lie in space, and does the understanding learn them by
merely endeavoring to find out the enormous wealth of meaning
that lies in space; or do they inhere in the understanding and in
the way in which it determines space according to the conditions
of the synthetical unity in which its concepts are all centered?

Space is something so uniform and as to all particular
properties so indeterminate, that we should certainly not seek a
store of laws of nature in it. Whereas that which determines
space to assume the form of a circle or the figures of a cone and
a sphere, is the understanding, so far as it contains the ground
of the unity of their constructions.

The mere universal form of intuition, called space, must
therefore be the substratum of all intuitions determinable to
particular objects, and in it of course the condition of the
possibility and of the variety of these intuitions lies. But the
unity of the objects is entirely determined by the understanding,
and on conditions which lie in its own nature; and thus the
understanding is the origin of the universal order of nature, in
that it comprehends all appearances under its own laws, and
thereby first constructs, a priori, experience (as to its form),
by means of which whatever is to be known only by experience, is
necessarily subjected to its laws. For we are not now concerned
with the nature of things in themselves, which is independent of
the conditions both of our sensibility and our understanding, but
with nature, as an object of possible experience, and in this
case the understanding, whilst it makes experience possible,
thereby insists that the sensuous world is either not an object
of experience at all, or must be nature [viz., an existence of
things, determined according to universal laws19].


Sect. 39. Of the System of the Categories.

There can be nothing more desirable to a philosopher, than
to be able to derive the scattered multiplicity of the concepts
or the principles, which had occurred to him in concrete use,
from a principle a priori, and to unite everything in this way in
one cognition. He formerly only believed that those things, which
remained after a certain abstraction, and seemed by comparison
among one another to constitute a particular kind of cognitions,
were completely collected; but this was only an Aggregate. Now he
knows, that just so many, neither more nor less, can constitute
the mode of cognition, and perceives the necessity of his
division, which constitutes comprehension; and now only he has
attained a System.

To search in our daily cognition for the concepts, which do
not rest upon particular experience, and yet occur in all
cognition of experience, where they as it were constitute the
mere form of connection, presupposes neither greater reflection
nor deeper insight, than to detect in a language the rules of the
actual use of words generally, and thus to collect elements for a
grammar. In fact both researches are very nearly related, even
though we are not able to give a reason why each language has
just this and no other formal constitution, and still less why an
exact number of such formal determinations in general are found
in it.

Aristotle collected ten pure elementary concepts under the
name of Categories.20 To these, which are also called
predicaments,21 he found himself obliged afterwards to add five
post-predicaments, some of which however (prius, simul, and
molus) are contained in the former; but this random collection
must be considered (and commended) as a mere hint for future
inquirers, not as a regularly developed idea, and hence it has,
in the present more advanced state of philosophy, been rejected
as quite useless.

After long reflection on the pure elements of human
knowledge (those which contain nothing empirical), I at last
succeeded in distinguishing with certainty and in separating the
pure elementary notions of the Sensibility (space and time) from
those of the Understanding. Thus the 7th, 8th, and 8th Categories
had to be excluded from the old list. And the others were of no
service to me; because there was no principle [in them], on which
the understanding could be investigated, measured in its
completion, and all the functions, whence its pure concepts
arise, determined exhaustively and with precision.

But in order to discover such a principle, I looked about
for an act of the understanding which comprises all the rest, and
is distinguished only by various modifications or phases, in
reducing the multiplicity of representation to the unity of
thinking in general: I found this act of the understanding to
consist in judging. Here then the labors of the logicians were
ready at hand, though not yet quite free from defects, and with
this help I was enabled to exhibit a complete table of the pure
functions of the understanding, which are however undetermined in
regard to any object. I finally referred these functions of
judging to objects in general, or rather to the condition of
determining judgments as objectively valid, and so there arose
the pure concepts of the understanding, concerning which I could
make certain, that these, and this exact number only, constitute
our whole cognition of things from pure understanding. I was
justified in calling them by their old name, Categories, while I
reserved for myself the liberty of adding, under the title of
"Predicables," a complete list of all the concepts deducible from
them, by combinations whether among themselves, or with the pure
form of the appearance, i.e., space or time, or with its matter,
so far as it is not yet empirically determined (viz., the object
of sensation in general), as soon as a system of transcendental
philosophy should be completed with the construction of which I
am engaged in the Critique of Pure Reason itself.

Now the essential point in this system of Categories, which
distinguishes it from the old rhapsodical collection without any
principle, and for which alone it deserves to be considered as
philosophy, consists in this: that by means of it the true
significance of the pure concepts of the understanding and the
condition of their use could be precisely determined. For here it
became obvious that they are themselves nothing but logical
functions, and as such do not produce the least concept of an
object, but require some sensuous intuition as a basis. They
therefore only serve to determine empirical judgments, which are
otherwise undetermined and indifferent as regards all functions
of judging, relatively to these functions, thereby procuring them
universal validity, and by means of them making judgments of
experience in general possible.

Such an insight into the nature of the categories, which
limits them at the same time to the mere use of experience, never
occurred either to their first author, or to any of his
successors; but without this insight (which immediately depends
upon their derivation or deduction), they are quite useless and
only a miserable list of names, without explanation or rule for
their use. Had the ancients ever conceived such a notion,
doubtless the whole study of the pure rational knowledge, which
under the name of metaphysics has for centuries spoiled many a
sound mind, would have reached us. in quite another shape, and
would have enlightened the human understanding, instead of
actually exhausting it in obscure and vain speculations, thereby
rendering it unfit for true science.

This system of categories makes all treatment of every
object of pure reason itself systematic, and affords a direction
or clue how and through what points of inquiry every metaphysical
consideration must proceed, in order to be complete; for it
exhausts all the possible movements (momenta) of the
understanding, among which every concept must be classed. In like
manner the table of Principles has been formulated, the
completeness of which we can only vouch for by the system of the
categories. Even in the division of the concepts,22 which must go
beyond the physical application of the understanding, it is
always the very same clue, which, as it must always be determined
a priori by the same fixed points of the human understanding,
always forms a closed circle. There is no doubt that the object
of a pure conception either of the understanding or of reason, so
far as it is to be estimated philosophically and on a priori
principles, can in this way be completely known. I could not
therefore omit to make use of this clue with regard to one of the
most abstract ontological divisions, viz., the various
distinctions of "the notions of something and of nothing," and to
construct accordingly (Critique, P. 207) a regular and necessary
table of their divisions.23

And this system, like every other true one founded on a
universal principle, shows its inestimable value in this, that it
excludes all foreign concepts, which might otherwise intrude
among the pure concepts of the understanding, and determines the
place of every cognition. Those concepts, which under the name of
"concepts of reflection" have been likewise arranged in a table
according to the clue of the categories, intrude, without having
any privilege or title to be among the pure concepts of the
understanding in Ontology. They are concepts of connection, and
thereby of the objects themselves, whereas the former are only
concepts of a mere comparison of concepts already given, hence of
quite another nature and use. By my systematic division24 they
are saved from this confusion. But the value of my special table
of the categories will be still more obvious, when we separate
the table of the transcendental concepts of Reason from the
concepts of the understanding. The latter being of quite another
nature and origin, they must have quite another form than the
former. This so necessary separation has never yet been made in
any system of metaphysics for, as a rule, these rational concepts
all mixed up with the categories, like children of one family,
which confusion was unavoidable in the absence of a definite
system of categories.


Sect. 40. Pure mathematics and pure science of nature had no
occasion for such a deduction, as we have made of both, for their
own safety and certainty. For the former rests upon its own
evidence; and the latter (though sprung from pure sources of the
understanding) upon experience and its thorough confirmation.
Physics cannot altogether refuse and dispense with the testimony
of the latter; because with all its certainty, it can never, as
philosophy, rival mathematics. Both sciences therefore stood in
need of this inquiry, not for themselves, but for the sake of
another science, metaphysics.

Metaphysics has to do not only with concepts of nature,
which always find their application in experience, but also with
pure rational concepts, which never can be given in any possible
experience. Consequently the objective reality of these concepts
(viz., that they are not mere chimeras), and the truth or falsity
of metaphysical assertions, cannot be discovered or confirmed by
any experience. This part of metaphysics however is precisely
what constitutes its essential end, to which the rest is only a
means, and thus this science is in need of such a deduction for
its, own sake. The third question now proposed relates therefore
as it were to the root and essential difference of metaphysics,
i.e., the occupation of Reason with itself, and the supposed
knowledge of objects arising immediately from this incubation of
its own concepts, without requiring, or indeed being able to
reach that knowledge through, experience.25

Without solving this problem reason never is justified. The
empirical use to which reason limits the pure understanding, does
not fully satisfy the proper destination of the latter. Every
single experience is only a part of the whole sphere of its
domain, but the absolute totality of all possible experience is
itself not experience. Yet it is a necessary [concrete] problem
for reason, the mere representation of which requires concepts
quite different from the categories, whose use is only immanent,
or refers to experience, so far as it can be given. Whereas the
concepts of reason aim at the completeness, i.e., the collective
unity of all possible experience, and thereby transcend every
given experience. Thus they become transcendent.

As the understanding stands in need of categories for
experience, reason contains in itself the source of ideas, by
which I mean necessary concepts, whose object cannot be given in
any experience. The latter are inherent in the nature of reason,
as the former are in that of the understanding. While the former
carry with them an illusion likely to mislead, the illusion of
the latter is inevitable, though it certainly can be kept from
misleading us.

Since all illusion consists in holding the subjective ground
of our judgments to be objective, a self-knowledge of pure reason
in its transcendent (exaggerated) use is the sole preservative
from the aberrations into which reason falls when it mistakes its
destination, and refers that to the object transcendently, which
only regards its own subject and its guidance in all immanent

Sect. 41. The distinction of ideas, that is, of pure
concepts of reason, from categories, or pure concepts of the
understanding, as cognitions of a quite distinct species, origin
and use, is so important a point in founding a science which is
to contain the system of all these a priori cognitions, that
without this distinction metaphysics is absolutely impossible, or
is at best a random, bungling attempt to build a castle in the
air without a knowledge of the materials or of their fitness for
any purpose. Had the Critique of Pure Reason done nothing but
first point out this distinction, it had thereby contributed more
to clear up our conception of, and to guide our inquiry in, the
field of metaphysics, than all the vain efforts which have
hitherto been made to satisfy the transcendent problems of pure
reason, without ever surmising that we were in quite another
field than that of the understanding, and hence classing concepts
of the understanding and those of reason together, as if they
were of the same kind.

Sect. 42. All pure cognitions of the understanding have this
feature, that their concepts present themselves in experience,
and their principles can be confirmed by it; whereas the
transcendent cognitions of reason cannot, either as ideas, appear
in experience, -or as propositions ever be confirmed or refuted
by it. Hence whatever errors may slip in unawares, can only be
discovered by pure reason itself-a discovery of much difficulty,
because this very reason naturally becomes dialectical by means
of its ideas, and this unavoidable illusion cannot be limited by
any objective and dogmatical researches into things, but by a
subjective investigation of reason itself as a source of ideas.

Sect. 43. In the Critique of Pure Reason it was always my
greatest care to endeavor not only carefully to distinguish the
several species of cognition, but to derive concepts belonging to
each one of them from their common source. I did this in order
that by knowing whence they originated, I might determine their
use with safety, and also have the unanticipated but invaluable
advantage of knowing the completeness of my enumeration,
classification and specification of concepts a priori, and
therefore according to principles. Without this, metaphysics is
mere rhapsody, in which no one knows whether he has enough, or
whether and where something is still wanting. We can indeed have
this advantage only in pure philosophy, but of this philosophy it
constitutes the very essence.

As I had found the origin of the categories in the four
logical functions of all the judgments of the understanding, it
was quite natural to seek the origin of the ideas in the three
functions of the syllogisms of reason. For as soon as these pure
concepts of reason (the transcendental ideas) are given, they
could hardly, except they be held innate, be found anywhere else,
than in the same activity of reason, which, so far as it regards
mere form, constitutes the logical element of the syllogisms of
reason; but, so far as it represents judgments of the
understanding with respect to the one or to the other form a
priori, constitutes transcendental concepts of pure reason.

The formal distinction of syllogisms renders their division
into categorical, hypothetical, and disjunctive necessary. The
concepts of reason founded on them contained therefore, first,
the idea of the complete subject (the substantial); secondly, the
idea of the complete series of conditions; thirdly, the
determination of all concepts in the idea of a complete complex
of that which is possible.26 The first idea is psychological, the
second cosmological, the third theological, and, as all three
give occasion to Dialectics, yet each in its own way, the
division of the whole Dialects of pure reason into its
Paralogism, its Antinomy, and its Ideal, was arranged
accordingly. Through this deduction we may feel assured that all
the claims of pure reason are completely represented, and that
none can be wanting; because the faculty of reason itself, whence
they all take their origin, is thereby completely surveyed.

Sect. 44. In these general considerations it is also
remarkable that the ideas of reason are unlike the categories, of
no service to the use of our understanding in experience, but
quite dispensable, and become even an impediment to the maxims of
a rational cognition of nature. Yet in another aspect still to be
determined they are necessary. Whether the soul is or is not a
simple substance, is of no consequence to us in the explanation
of its phenomena. For we cannot render the notion of a simple
being intelligible by any possible experience that is sensuous or
concrete. The notion is therefore quite void as regards all
hoped-for insight into the cause of phenomena, and cannot at all
serve as a principle of the explanation of that which internal or
external experience supplies. So the cosmological ideas of the
beginning of the world or of its eternity (a parte ante) cannot
be of any greater service to us for the explanation of any event
in the world itself. And finally we must, according to a right
maxim of the philosophy of nature, refrain from all explanations
of the design of nature, drawn from the will of a Supreme Being;
because this would not be natural philosophy, but an
acknowledgment that we have come to the end of it. The use of
these ideas, therefore, is quite different from that of those
categories by which (and by the principles built upon which)
experience itself first becomes possible. But our laborious
analytics of the understanding would be superfluous if we had
nothing else in view than the mere cognition Of nature as it can
be given in experience; for reason does its work, both in
mathematics and in the science of nature, quite safely and well
without any of this subtle deduction. Therefore our Critique of
the Understanding combines with the ideas of pure reason for a
purpose which lies beyond the empirical use of the understanding;
but this we have above declared to be in this aspect totally
inadmissible, and without any object or meaning. Yet there must
be a harmony between that of the nature of reason and that of the
understanding, and the former must contribute to the perfection
of the latter, and cannot possibly upset it.

The solution of this question is as follows: Pure reason
does not in its ideas point to particular objects, which lie
beyond the field of experience, but only requires completeness of
the use of the understanding in the system of experience. But
this completeness can be a completeness of principles only, not
of intuitions [i.e., concrete atsights or Anschauungen] and of
objects. In order however to represent the ideas definitely,
reason conceives them after the fashion of the cognition of an
object. The cognition is as far as these rules are concerned
completely determined, but the object is only an idea invented
for the purpose of bringing the cognition of the understanding as
near as possible to the completeness represented by that idea.

Prefatory Remark to the Dialectics of Pure Reason.

Sect. 45. We have above shown in Sect. Sect. 33 and 34 that
the purity of the categories from all admixture of sensuous
determinations may mislead reason into extending their use, quite
beyond all experience, to things in themselves; though as these
categories themselves find no intuition which can give them
meaning or sense in concrete, they, as mere logical functions,
can represent a thing in general, but not give by themselves
alone a determinate concept of anything. Such hyperbolical
objects are distinguished by the appellation of Noumena, or pure
beings of the understanding (or better, beings of thought), such
as, for example, "substance," but conceived without permanence in
time, or "cause," but not acting in time, etc. Here predicates,
that only serve to make the conformity-to-law of experience
possible, are applied to these concepts, and yet they are
deprived of all the conditions of intuition, on which alone
experience is possible, and so these concepts lose all

There is no danger, however, of the understanding
spontaneously making an excursion so very wantonly beyond its own
bounds into the field of the mere creatures of thought, without
being impelled by foreign laws. But when reason, which cannot be
fully satisfied with any empirical use of the rules of the
understanding, as being always conditioned, requires a completion
of this chain of conditions, then the understanding is forced out
of its sphere. And then it partly represents objects of
experience in a series so extended that no experience can grasp,
partly even (with a view to complete the series) it seeks
entirely beyond it noumena, to which it can attach that chain,
and so, having at last escaped from the conditions of experience,
make its attitude as it were final. These are then the
transcendental ideas, which, though according to the true but
hidden ends of the natural determination of our reason, they may
aim not at extravagant concepts, but at an unbounded extension of
their empirical use, yet seduce the understanding by an
unavoidable illusion to a transcendent use, which, though
deceitful, cannot be restrained within the bounds of experience
by any resolution, but only by scientific instruction and with
much difficulty.

!. The Psychological Idea.27

Sect. 46. People have long since observed, that in all
substances the proper subject, that which remains after all the
accidents (as predicates) are abstracted, consequently that which
forms the substance of things remains unknown, and various
complaints have been made concerning these limits to our
knowledge. But it will be well to consider that the human
understanding is not to be blamed for its inability to know the
substance of things, that is, to determine it by itself, but
rather for requiring to know it which is a mere idea definitely
as though it were a given object. Pure reason requires us to seek
for every predicate of a thing its proper subject, and for this
subject, which is itself necessarily nothing but a predicate, its
subject, and so on indefinitely (or as far as we can reach). But
hence it follows, that we must not hold anything, at which we can
arrive, to be an ultimate subject, and that substance itself
never can be thought by our understanding, however deep we may
penetrate, even if all nature were unveiled to us. For the
specific nature of our understanding consists in thinking
everything discursively, that is, representing it by concepts,
and so by mere predicates, to which therefore the absolute
subject must always be wanting. Hence all the real properties, by
which we know bodies, are mere accidents, not excepting
impenetrability, which we can only represent to ourselves as the
effect of a power of which the subject is unknown to us.

Now we appear to have this substance in the consciousness of
ourselves (in the thinking subject), and indeed in an immediate
intuition; for all the predicates of an internal sense refer to
the ego, as a subject, and I cannot conceive myself as the
predicate of any other subject. Hence completeness in the
reference of the given concepts as predicates to a subject -- not
merely an idea, but an object-that is, the absolute subject
itself, seems to be given in experience. But this expectation is
disappointed. For the ego is not a concept,28 but only the
indication of the object of the internal sense, so far as we know
it by no further predicate. Consequently it cannot be in itself a
predicate of any other thing; but just as little can it be a
determinate concept of an absolute subject, but is, as in all
other cases, only the reference of the internal phenomena to
their unknown subject. Yet this idea (which serves very well, as
a regulative principle, totally to destroy all materialistic
explanations of the internal phenomena of the soul) occasions by
a very natural misunderstanding a very specious argument, which,
from this supposed cognition of the substance of our thinking
being, infers its nature, so far as the knowledge of it falls
quite without the complex of experience.

Sect. 47. But though we may call this thinking self (the
soul) substance, as being the ultimate subject of thinking which
cannot be further represented as the predicate of another thing;
it remains quite empty and without significance, if permanence-
the quality which renders the concept of substances in experience
fruitful-cannot be proved of it.

But permanence can never be proved of the concept of a
substance, as a thing in itself, but for the purposes of
experience only. This is sufficiently shown by the first Analogy
of Experience,29 and whoever will not yield to this proof may try
for himself whether he can succeed in proving, from the concept
of a subject which does not exist itself as the predicate of
another thing, that its existence is thoroughly permanent, and
that it cannot either in itself or by any natural cause original
or be annihilated. These synthetical a priori propositions can
never be proved in themselves, but only in reference to things as
objects of possible experience.

Sect. 48. If therefore from the concept of the soul as a
substance, we would infer its permanence, this can hold good as
regards possible experience only, not [of the soul] as a thing in
itself and beyond all possible experience. But life is the
subjective condition of all our possible experience, consequently
we can only infer the permanence of the soul in life; for the
death of man is the end of all experience which concerns the soul
as an object of experience, except the contrary be proved, which
is the very question in hand. The permanence of the soul can
therefore only be proved (and no one cares for that) during the
life of man, but not, as we desire to do, after death; and for
this general reason, that the concept of substance, so far as it
is to be considered necessarily combined with the concept of
permanence, can be so combined only according to the principles
of possible experience, and therefore for the purposes of
experience only.30

Sect. 49. That there is something real without us which not
only corresponds, but must correspond, to our external
perceptions, can likewise be proved to be not a connection of
things in themselves, but for the sake of experience. This means
that there is something empirical, i.e., some phenomenon in space
without us, that admits of a satisfactory proof, for we have
nothing to do with other objects than those which belong to
possible experience; because objects which cannot be given us in
any experience, do not exist for us. Empirically without me is
that which appears in space, and space, together with all the
phenomena which it contains, belongs to the representations,
whose connection according to laws of experience proves their
objective truth, just as the connection of the phenomena of the
internal sense proves the actuality of my soul (as an object of
the internal sense). By means of external experience I am
conscious of the actuality of bodies, as external phenomena in
space, in the same manner as by means of the internal experience
I am conscious of the existence of my soul in time, but this soul
is only known as an object of the internal sense by phenomena
that constitute an internal state, and of which the essence in
itself, which forms the basis of these phenomena, is unknown.
Cartesian idealism therefore does nothing but distinguish
external experience from dreaming; and the conformity to law (as
a criterion of its truth) of the former, from the irregularity
and the false illusion of the latter. In both it presupposes
space and time as conditions of the existence of objects, and it
only inquires whether the objects of the external senses, which
we when awake put in space, are as actually to be found in it, as
the object of the internal sense, the soul, is in time; that is,
whether experience carries with it sure criteria to distinguish
it from imagination. This doubt, however, may easily be disposed
of, and we always do so in common life by investigating the
connection of phenomena in both space and time according to
universal laws of experience, and we cannot doubt, when the
representation of external things throughout agrees therewith,
that they constitute truthful experience. Material idealism, in
which phenomena are considered as such only according to their
connection in experience, may accordingly be very easily refuted;
and it is just as sure an experience, that bodies exist without
us (in space), as that I myself exist according to the
representation of the internal sense (in time): for the notion
without us, only signifies existence in space. However as the Ego
in the proposition, III am," means not only the object of
internal intuition (in time), but the subject of consciousness,
just as body means not only external intuition (in space), but
the thing-in-itself, which is the basis of this phenomenon; [as
this is the case] the question, whether bodies (as phenomena of
the external sense) exist as bodies apart from my thoughts, may
without any hesitation be denied in nature. But the question,
whether I myself as a phenomenon of the internal sense (the soul
according to empirical psychology) exist apart from my faculty of
representation in time, is an exactly similar inquiry, and must
likewise be answered in the negative. Arid in this manner
everything, when it is reduced to its true meaning, is decided
and certain. The formal (which I have also called transcendental)
actually abolishes the material, or Cartesian, idealism. For if
space be nothing but a form of my sensibility, it is as a
representation in me just as actual as I myself am, and nothing
but the empirical truth of the representations in it remains for
consideration. But, if this is not the case, if space and the
phenomena in it are something existing without us, then all the
criteria of experience beyond our perception can never prove the
actuality of these objects without us.

II. The Cosmological Idea.31

Sect. 50. This product of pure reason in its transcendent
use is its most remarkable curiosity. It serves as a very
powerful agent to rouse philosophy from its dogmatic slumber, and
to stimulate it to the arduous task of undertaking a Critique of
Reason itself.

I term this idea cosmological, because it always takes its
object only from the sensible world, and does not use any other
than those whose object is given to sense, consequently it
remains in this respect in its native home, it does not become
transcendent, and is therefore so far not mere idea; whereas, to
conceive the soul as a simple substance, -already means to
conceive such an object (the simple) as cannot be presented to
the senses. Yet the cosmological idea extends the connection of
the conditioned with its condition (whether the connection is
mathematical or dynamical) so far, that experience never can keep
up with it. It is therefore with regard to this point always an
idea, whose object never can be adequately given in any

Sect. 51. In the first place, the use of a system of
categories becomes here so obvious and unmistakable, that even if
there were not several other proofs of it, this alone would
sufficiently prove it indispensable in the system of pure reason.
There are only four such transcendent ideas, as there are so many
classes of categories; in each of which, however, they refer only
to the absolute completeness of the series of the conditions for
a given conditioned. In analogy to these cosmological ideas there
are only four kinds of dialectical assertions of pure reason,
which, as they are dialectical, thereby prove, that to each of
them, oii equally specious principles of pure reason, a
contradictory assertion stands opposed. As all the metaphysical
art of the most subtle distinction cannot prevent this
opposition, it compels the philosopher to recur to the first
sources of pure reason itself. This Antinomy, not arbitrarily
invented, but founded in the nature of human reason, and hence
unavoidable and never ceasing, contains the following four theses
together with their antitheses:

Thesis: The World has, as to, Time and Space, a Beginning
Antithesis: The World is, as to Time and Space, infinite.
Thesis: Everything in the World consists of [elements that
are] simple.
Antithesis: There is nothing simple, but everything is
Thesis: There are in the World Causes through Freedom.
Antithesis: There is no Liberty, but all is Nature.
Thesis: In the Series of the World-Causes there is some
necessary Being.
Antithesis: There is Nothing necessary in the World, but in
this Series All is incidental.

Sect. 52. a. Here is the most singular phenomenon of human
reason, no other instance of which can be shown in any other use.
If we, as is commonly done, represent to ourselves the
appearances of the sensible world as things in themselves, if we
assume the principles of their combination as principles
universally valid of things in themselves and not merely of
experience, as is usually, nay without our Critique, unavoidably
done, there arises an unexpected conflict, which never can be
removed in the common dogmatical way; because the thesis, as well
as the antithesis, can be shown by equally clear, evident, and
irresistible proofs-for I pledge myself as to the correctness of
all these proofs-and reason therefore perceives that it is
divided with itself, a state at which the skeptic rejoices, but
which must make the critical philosopher pause and feel ill at

Sect. 52. b. We may blunder in various ways in metaphysics
without any fear of being detected in falsehood. For we never can
be refuted by experience if we but avoid self-contradiction,
which in synthetical, though purely fictitious propositions, may
be done whenever the concepts, which we connect, are mere ideas,
that cannot be given (in their whole content) in experience. For
how can we make out by experience, whether the world is from
eternity or had a beginning, whether matter is infinitely
divisible or consists of simple parts? Such concept cannot be
given in any experience, be it ever so extensive, and
consequently the falsehood either of the positive or the negative
proposition cannot be discovered by this touchstone.

The only possible way in which reason could have revealed
unintentionally its secret Dialectics, falsely announced as
Dogmatics, would be when it were made to ground an assertion upon
a universally admitted principle, and to deduce the exact
contrary with the greatest accuracy of inference from another
which is equally granted. This is actually here the case with
regard to four natural ideas of reason, whence four assertions on
the one side, and as many counter-assertions on the other arise,
each consistently following from universally-acknowledged
principles. Thus they reveal by the use of these principles the
dialectical illusion of pure reason which would otherwise forever
remain concealed.

This is therefore a decisive experiment, which must
necessarily expose any error lying hidden in the assumptions of
reason.32 Contradictory propositions cannot both be false, except
the concept, which is the subject of both, is self-contradictory;
for example, the propositions, "a square circle is round, and a
square circle is not round," are both false. For, as to the
former it is false, that the circle is round, because it is
quadrangular; and it is likewise false, that it is not round,
that is, angular, because it is a circle. For the logical
criterion of the impossibility of a concept consists in this,
that if we presuppose it, two contradictory propositions both
become false; consequently, as no middle between them is
conceivable, nothing at all is thought by that concept.

Sect. 52. c. The first two antinomies, which I call
mathematical, because they are concerned with the addition or
division of the homogeneous, are founded on such a self-
contradictory concept; and hence I explain how it happens, that
both the Thesis and Antithesis of the two are false.

When I speak of objects in time and in space, it is not of
things in themselves, of which I know nothing, but of things in
appearance, that is, of experience, as the particular way of
cognising objects which is afforded to man. I must not say of
what I think in time or in space, that in itself, and independent
of these my thoughts, it exists in space and in time; for in that
case I should contradict myself; because space and time, together
with the appearances in them, are nothing existing in themselves
and outside of my representations, but are themselves only modes
of representation, and it is palpably contradictory to say, that
a mere mode of representation exists without our representation.
Objects of the senses therefore exist only in experience; whereas
to give them a self-subsisting existence apart from experience or
before it, is merely to represent to ourselves that experience
actually exists apart from experience or before it.

Now if I inquire after the quantity of the world, as to
space and time, it is equally impossible, as regards all my
notions, to declare it infinite or to declare it finite. For
neither assertion can be contained in experience, because
experience either of an infinite space, or of an infinite time
elapsed, or again, of the boundary of the world by a void space,
or by an antecedent void time, is impossible; these are mere
ideas. This quantity of the world, which is determined in either
way, should therefore exist in the world itself apart from all
experience. This contradicts the notion of a world of sense,
which is merely a complex of the appearances whose existence and
connection occur only in our representations, that is, in
experience, since this latter is not an object in itself, but a
mere mode of representation. Hence it follows, that as the
concept of an absolutely existing world of sense is self-
contradictory, the solution of the problem concerning its
quantity, whether attempted affirmatively or negatively, is
always false.

The same holds good of the second antinomy, which relates to
the division of phenomena. For these are mere representations,
and the parts exist merely in their representation, consequently
in the division, or in a possible experience where they are
given, and the division reaches only as far as this latter
reaches. To assume that an appearance, e.g., that of body,
contains in itself before all experience all the parts, which any
possible experience can ever reach, is to impute to a mere
appearance, which can exist only in experience, an existence
previous to experience. In other words, it would mean that mere
representations exist before they can be found in our faculty of
representation. Such an assertion is self-contradictory, as also
every solution of our misunderstood problem, whether we maintain,
that bodies in themselves consist of an infinite number of parts,
or of a finite number of simple parts.

Sect. 53. In the first (the mathematical) class of
antinomies the falsehood of the assumption consists in
representing in one concept something self-contradictory as if it
were compatible (i.e., an appearance as an object in itself).
But, as to the second (the dynamical) class of antinomies, the
falsehood of the representation consists in representing as
contradictory what is compatible; so that, as in the former case,
the opposed assertions are both false, in this case, on the other
hand, where they are opposed to one another by mere
misunderstanding, they may both be true.

Any mathematical connection necessarily presupposes
homogeneity of what is connected (in the concept of magnitude),
while the dynamical one by no means requires the same. When we
have to deal with extended magnitudes, all the parts must be
homogeneous with one another and with the whole; whereas, in the
connection of cause and effect, homogeneity may indeed likewise
be found, but is not necessary; for the concept of causality (by
means of which something is posited through something else quite
different from it), at all events, does not require it.

If the objects of the world of sense are taken for things in
themselves, and the above laws of nature for the laws of things
in themselves, the contradiction would be unavoidable. So also,
if the subject of freedom were, like other objects, represented
as mere appearance, the contradiction would be just as
unavoidable, for the same predicate would at once be affirmed and
denied of the same kind of object in the same sense. But if
natural necessity is referred merely to appearances, and freedom
merely to things in themselves, no contradiction arises, if we at
once assume, or admit both kinds of causality, however difficult
or impossible it may be to make the latter kind conceivable.

As appearance every effect is an event, or something that
happens in time; it must, according to the universal law of
nature, be preceded by a determination of the causality of its
cause (a state), which follows according to a constant law. But
this determination of the cause as causality must likewise be
something that takes place or happens; the cause must have begun
to act, otherwise no succession between it and the effect could
be conceived. Otherwise the effect, as well as the causality of
the cause, would have always existed. Therefore the determination
of the cause to act must also have originated among appearances,
and must consequently, as well as its effect, be an event, which
must again have its cause, and so on; hence natural necessity
must be the condition, on which effective causes are determined.
Whereas if freedom is to be a property of certain causes of
appearances, it must, as regards these, which are events, be a
faculty of starting them spontaneously, that is, without the
causality of the cause itself, and hence without requiring any
other ground to determine its start. But then the cause, as to
its causality, must not rank under time-determinations of its
state, that is, it cannot be an appearance, and must be
considered a thing in itself, while its effects would be only
appearances.33 If without contradiction we can think of the
beings of understanding [Verstandeswesen] as exercising such an
influence on appearances, then natural necessity will attach to
all connections of cause and effect in the .sensuous world,
though on the other hand, freedom can be granted to such cause,
as is itself not an appearance (but the foundation of
appearance). Nature therefore and freedom can without
contradiction be attributed to the very same thing, but in
different relations-on one side as a phenomenon, on the other as
a thing in itself.

We have in us a faculty, which not only stands in connection
with its subjective determining grounds that are the natural
causes of its actions, and is so far the faculty of a being that
itself belongs to appearances, but is also referred to objective
grounds, that are only ideas, so far as they can determine this
faculty, a connection which is expressed by the word ought. This
faculty is called reason, and, so far as we consider a being
(man) entirely according to this objectively determinable reason,
he cannot be considered as a being of sense, but this property is
that of a thing in itself, of which we cannot comprehend the
possibility-I mean how the ought (which however has never yet
taken place) should determine its activity, and can become the
cause of actions, whose effect is an appearance in the sensible
world. Yet the causality of reason would be freedom with regard
to the effects in the sensuous world, so far as we can consider
objective grounds, which are themselves ideas, as their
determinants. For its action in that case would not depend upon
subjective conditions, consequently not upon those of time, and
of course not upon the law of nature, which serves to determine
them, because grounds of reason give to actions the rule
universally, according to principles, without the influence of
the circumstances of either time or place.

What I adduce here is merely meant as an example to make the
thing intelligible, and does not necessarily belong to our
problem, which must be decided from mere concepts, independently
of the properties which we meet in the actual world.

Now I may say without contradiction: that all the actions of
rational beings, so far as they are appearances (occurring in any
experience), are subject to the necessity of nature; but the same
actions, as regards merely the rational subject and its faculty
of acting according to mere reason, are free. For what is
required for the necessity of nature? Nothing more than the
determinability of every event in the world of sense according to
constant laws, that is, a reference to cause in the appearance;
in this process the thing in itself at its foundation and its
causality remain unknown. But I say, that the law of nature
remains, whether the rational being is the cause of the effects
in the sensuous world from reason, that is, through freedom, or
whether it does not determine them on grounds of reason. For, if
the former is the case, the action is performed according to
maxims, the effect of which as appearance is always conformable
to constant laws; if the latter is the case, and the action not
performed on principles of reason, it is subjected to the
empirical laws of the sensibility, and in both cases the effects
are connected according to constant laws; more than this we do
not require or know concerning natural necessity. But in the
former case reason is the cause of these laws of nature, and
therefore free; in the latter the effects follow according to
mere natural laws of sensibility, because reason does not
influence it; but reason itself is not determined on that account
by the sensibility, and is therefore free in this case too.
Freedom is therefore no hindrance to natural law in appearance,
neither does this law abrogate the freedom of the practical use
of reason, which is connected with things in themselves, as
determining grounds.

Thus practical freedom, viz., the freedom in which reason
possesses causality according to objectively determining grounds,
is rescued and yet natural necessity is not in the least
curtailed with regard to the very same effects, as appearances.
The same remarks will serve to explain what we had to say
concerning transcendental freedom and its compatibility with
natural necessity (in the same subject, but not taken in the same
reference). For, as to this, every beginning of the action of a
being from objective causes regarded as determining grounds, is
always a first start, though the same action is in the series of
appearances only a subordinate start, which must be preceded by a
state of the cause, which determines it, and is itself determined
in the same manner by another immediately preceding. Thus we are
able, in rational beings, or in beings generally, so far as their
causality is determined in them as things in themselves, to
imagine a faculty of beginning from itself a series of states,
without falling into contradiction with the laws of nature. For
the relation of the action to objective grounds of reason is not
a time-relation; in this case that which determines the causality
does not precede in time the action, because such determining
grounds represent not a reference to objects of sense, e.g., to
causes in the appearances, but to determining causes, as things
in themselves, which do not rank under conditions of time. And in
this way the action, with regard to the causality of reason, can
be considered as a first start in respect to the series of
appearances, and yet also as a merely subordinate beginning. We
may therefore without contradiction consider it in the former
aspect as free, but in the latter (in so far as it is merely
appearance) as subject to natural necessity.

As to the fourth Antinomy, it is solved in the same way as
the conflict of reason with itself in the third. For, provided
the cause in the appearance is distinguished from the cause of
the appearance (so far as it can be thought as a thing in
itself), both propositions are perfectly reconcilable: the one,
that there is nowhere in the sensuous world a cause (according to
similar laws of causality), whose existence is absolutely
necessary; the other, that this world is nevertheless connected
with a Necessary Being as its cause (but of another kind and
according to another law). The incompatibility of these
propositions entirely rests upon the mistake of extending what is
valid merely of appearances to things in themselves, and in
general confusing both in one concept.

Sect. 54. This then is the proposition and this the solution
of the whole antinomy, in which reason finds itself involved in
the application of its principles to the sensible world. The
former alone (the mere proposition) would be a considerable
service in the cause of our knowledge of human reason, even
though the solution might fail to fully satisfy the reader, who
has here to combat a natural illusion, which has been but
recently exposed to him, and which he had hitherto always
regarded as genuine. For one result at least is unavoidable. As
it is quite impossible to prevent this conflict of reason with
itself-so long as the objects of the sensible world are taken for
things in themselves, and not for mere appearances, which they
are in fact-the reader is thereby compelled to examine over again
the deduction of all our a priori cognition and the proof which I
have given of my deduction in order to come to a decision on the
question. This is all I require at present; for when in this
occupation he shall have thought himself deep enough into the
nature of pure reason, those concepts by which alone the solution
of the conflict of reason is possible, will become sufficiently
familiar to him. Without this preparation I cannot expect an
unreserved assent even from the most attentive reader.

III. The Theological Idea.34

Sect. 55. The third transcendental Idea, which affords
matter for the most important, but, if pursued only
speculatively, transcendent and thereby dialectical use of
reason, is the ideal of pure reason. Reason in this case does
not, as with the psychological and the cosmological Ideas, begin
from experience, and err by exaggerating its grounds, in striving
to attain, if possible, the absolute completeness of their
series. It rather totally breaks with experience, and from mere
concepts of what constitutes the absolute completeness of a thing
in general, consequently by means of the idea of a most perfect
primal Being, it proceeds to determine the possibility and
therefore the actuality of all other things. And so the mere
presupposition of a Being, who is conceived not in the series of
experience, yet for the purposes of experience-for the sake of
comprehending its connection, order, and unity -i.e., the idea
[the notion of it], is more easily distinguished from the concept
of the understanding here, than in the former cases. Hence we can
easily expose the dialectical illusion which arises from our
making the subjective conditions of our thinking objective
conditions of objects themselves, and an hypothesis necessary for
the satisfaction of our reason, a dogma. As the observations of
the Critique on the pretensions of transcendental theology are
intelligible, clear, and decisive, I have nothing more to add on
the subject.

General Remark on the Transcendental Ideas.

Sect. 56. The objects, which are given us by experience, are
in many respects incomprehensible, and many questions, to which
the law of nature leads us, when carried beyond a certain point
(though quite conformably to the laws of nature), admit of no
answer; as for example the question: why substances attract one
another? But if we entirely quit nature, or in pursuing its
combinations, exceed all possible experience, and so enter the
realm of mere ideas, we cannot then say that the object is
incomprehensible, and that the nature of things proposes to us
insoluble problems. For we are not then concerned with nature or
in general with given objects, but with concepts, which have
their origin merely in our reason, and with mere creations of
thought; and all the problems that arise from our notions of them
must be solved, because of course reason can and must give a full
account of its own procedure.35 As the psychological,
cosmological, and theological Ideas are nothing but pure concepts
of reason, which cannot be given in any experience, the questions
which reason asks us about them are put to us not by the objects,
but by mere maxims of our reason for the sake of its own
satisfaction. They must all be capable of satisfactory answers,
which is done by showing that they are principles which bring our
use of the understanding into thorough agreement, completeness,
and synthetical unity, and that they so far hold good of
experience only, but of experience as a whole.

Although an absolute whole of experience is impossible, the
idea of a whole of cognition according to principles must impart
to our knowledge a peculiar kind of unity, that of a system,
without which it is nothing but piecework, and cannot be used for
proving the existence of a highest purpose (which can only be the
general system of all purposes), I do not here refer only to the
practical, but also to the highest purpose of the speculative use
of reason.

The transcendental Ideas therefore express the peculiar
application of reason as a principle of systematic unity in the
use of the understanding. Yet if we assume this unity of the mode
of cognition to be attached to the object of cognition, if we
regard that which is merely regulative to be constitutive, and if
we persuade ourselves that we can by means of these Ideas enlarge
our cognition transcendently, or far beyond all possible
experience, while it only serves to render experience within
itself as nearly complete as possible, i.e., to limit its
progress by nothing that cannot belong to experience: we suffer
from a mere misunderstanding in our estimate of the proper
application of our reason and of its principles, and from a
Dialectic, which both confuses the empirical use of reason, and
also sets reason at variance with itself.

* * * *


Sect. 57. Having adduced the clearest arguments, it would be
absurd for us to hope that we can know more of any object, than
belongs to the possible experience of it, or lay claim to the
least atom of knowledge about anything not assumed to be an
object of possible experience, which would determine it according
to the constitution it has in itself. For how could we determine
anything in this way, since time, space, and the categories, and
still more all the concepts formed by empirical experience or
perception in the sensible world [Anschauung], have and can have
no other use, than to make experience possible. And if this
condition is omitted from the pure concepts of the understanding,
they do not determine any object, and have no meaning whatever.

But it would be on the other hand a still greater absurdity
if we conceded no things in themselves, or set up our experience
for the only possible mode of knowing things, our way of
beholding [Anschauung] them in space and in time for the only
possible way, and our discursive understanding for the archetype
of every possible understanding; in fact if we wished to have the
principles of the possibility of experience considered universal
conditions of things in themselves.

Our principles, which limit the use of reason to possible
experience, might in this way become transcendent, and the limits
of our reason be set up as limits of the possibility of things in
themselves (as Hume's dialogues may illustrate), if a careful
critique did not guard the bounds of our reason with respect to
its empirical use, and set a limit to its pretensions. Skepticism
originally arose from metaphysics and its licentious dialectics.
At first it might, merely to favor the empirical use of reason,
announce everything that transcends this use as worthless and
deceitful; but by and by, when it was perceived that the very
same principles that are used in experience, insensibly, and
apparently with the same right, led still further than experience
extends, then men began to doubt even the propositions of
experience. But here there is no danger; for common sense will
doubtless always assert its rights. A certain confusion, however,
arose in science which cannot determine how far reason is to be
trusted, and why only so far and no further, and this confusion
can only be cleared up and all future relapses obviated by a
formal determination, on principle, of the boundary of the use of
our reason.

We cannot indeed, beyond all possible experience, form a
definite notion of what things in themselves may be. Yet we are
not at liberty to abstain entirely from inquiring into them; for
experience never satisfies reason fully, but in answering
questions, refers us further and further back, and leaves us
dissatisfied with regard to their complete solution. This any one
may gather from the Dialectics of pure reason, which therefore
has its good subjective grounds. Having acquired, as regards the
nature of our soul, a clear conception of the subject, and having
come to the conviction, that its manifestations cannot be
explained materialistically, who can refrain from asking what the
soul really is, and, if no concept of experience suffices for the
purpose, from accounting for it by a concept of reason (that of a
simple immaterial being), though we cannot by any means prove its
objective reality? Who can satisfy himself with mere empirical
knowledge in all the cosmological questions of the duration and
of the quantity of the world, of freedom or of natural necessity,
since every answer given on principles of experience begets a
fresh question, which likewise requires its answer and thereby
clearly shows the insufficiency of all physical modes of
explanation to satisfy reason? Finally, who does not see in the
thoroughgoing contingency and dependence of all his thoughts and
assumptions on mere principles of experience, the impossibility
of stopping there? And who does not feel himself compelled,
notwithstanding all interdictions against losing himself in
transcendent ideas, to seek rest and contentment beyond all the
concepts which he can vindicate by experience, in the concept of
a Being, the possibility of which we cannot conceive, but at the
same time cannot be refuted, because it relates to a mere being
of the understanding, and without it reason must needs remain
forever dissatisfied?

Bounds (in extended beings) always presuppose a space
existing outside a certain definite place, and enclosing it;
limits do not require this, but are mere negations, which affect
a quantity, so far as it is not absolutely complete. But our
reason, as it were, sees in its surroundings a space for the
cognition of things in themselves, though we can never have
definite notions of them, and are limited to appearances only.

As long as the cognition of reason is homogeneous, definite
bounds to it are inconceivable. In mathematics and in natural
philosophy human reason admits of limits but not of bounds, viz.,
that something indeed lies without it, at which it can never
arrive, but not that it will at any point find completion in its
internal progress. The enlarging of our views in mathematics, and
the possibility of new discoveries, are infinite; and the same is
the case with the discovery of new properties of nature, of new
powers and laws, by continued experience and its rational
combination. But limits cannot be mistaken here, for mathematics
refers to appearances only, and what cannot be an object of
sensuous contemplation, such as the concepts of metaphysics and
of morals, lies entirely without its sphere, and it can never
lead to them; neither does it require them. It is therefore not a
continual progress and an approximation towards these sciences,
and there is not, as it were, any point or line of contact.
Natural science will never reveal to us the internal constitution
of things, which though not appearance, yet can serve as the
ultimate ground of explaining appearance. Nor does that science
require this for its physical explanations. Nay even if such
grounds should be offered from other sources (for instance, the
influence of immaterial beings), they must be rejected and not
used in the progress of its explanations. For these explanations
must only be grounded upon that which as an object of sense can
belong to experience, and be brought into connection with our
actual perceptions and empirical laws.

But metaphysics leads us towards bounds in the dialectical
attempts of pure reason (not undertaken arbitrarily or wantonly,
but stimulated thereto by the nature of reason itself). And the
transcendental Ideas, as they do not admit of evasion, and are
never capable of realization, serve to point out to us actually
not only the bounds of the pure use of reason, but also the way
to determine them. Such is the end and the use of this natural
predisposition of our reason, which has brought forth metaphysics
as its favorite child, whose generation, like every other in the
world, is not to be ascribed to blind chance, but to an original
germ, wisely organized for great ends. For metaphysics, in its
fundamental features, perhaps more than any other science, is
placed in us by nature itself, and cannot be considered the
production of an arbitrary choice or a casual enlargement in the
progress of experience from which it is quite disparate.

Reason with all its concepts and laws of the understanding,
which suffice for empirical use, i.e., within the sensible world,
finds in itself no satisfaction because ever-recurring questions
deprive us of all hope of their complete solution. The
transcendental ideas, which have that completion in view, are
such problems of reason. But it sees clearly, that the sensuous
world cannot contain this completion, neither consequently can
all the concepts, which serve merely for understanding the world
of sense, such as space and time, and whatever we have adduced
under the name of pure concepts of the understanding. The
sensuous world is nothing but a chain of appearances connected
according to universal laws; it has therefore no subsistence by
itself; it is not the thing in itself, and consequently must
point to that which contains the basis of this experience, to
beings which cannot be known merely as phenomena, but as things
in themselves. In the cognition of them alone reason can hope to
satisfy its desire of completeness in proceeding from the
conditioned to its conditions.

We have above (Sects. 33, 34) indicated the limits of reason
with regard to all cognition of mere creations of thought. Now,
since the transcendental ideas have urged us to approach them,
and thus have led us, as it were, to the spot where the occupied
space (viz., experience) touches the void (that of which we can
know nothing, viz., noumena), we can determine the bounds of pure
reason. For in all bounds there is something positive (e.g., a
surface is the boundary of corporeal space, and is therefore
itself a space, a line is a space, which is the boundary of the
surface, a point the boundary of the line, but yet always a place
in space), whereas limits contain mere negations. The limits
pointed out in those paragraphs are not enough after we have
discovered that beyond them there still lies something (though we
can never know what it is in itself). For the question now is,
What is the attitude of our reason in this connection of what we
know with what we do not, and never shall, know? This is an
actual connection of a known thing with one quite unknown (and
which will always remain so), and though what is unknown should
not become the least more known-which we cannot even hope-yet the
notion of this connection must be definite, and capable of being
rendered distinct.

We must therefore accept an immaterial being, a world of
understanding, and a Supreme Being (all mere noumena), because in
them only, as things in themselves, reason finds that completion
and satisfaction, which it can never hope for in the derivation
of appearances from their homogeneous grounds, and because these
actually have reference to something distinct from them (and
totally heterogeneous), as appearances always presuppose an
object in itself, and therefore suggest its existence whether we
can know more of it or not.

But as we can never know these beings of understanding as
they are in themselves, that is, definitely, yet must assume them
as regards the sensible world, and connect them with it by
reason, we are at least able to think this connection by means of
such concepts as express their relation to the world of sense.
Yet if we represent to ourselves a being of the understanding by
nothing but pure concepts of the understanding, we then indeed
represent nothing definite to ourselves, consequently our concept
has no significance; but if we think it by properties borrowed
from the sensuous world, it is no longer a being of
understanding, but is conceived as an appearance, and belongs to
the sensible world. Let us take an instance from the notion of
the Supreme Being.

Our deistic conception is quite a pure concept of reason,
but represents only a thing containing all realities, without
being able to determine any one of them; because for that purpose
an example must be taken from the world of sense, in which case
we should have an object of sense only, not something quite
heterogeneous, which can never be an object of sense. Suppose I
attribute to the Supreme Being understanding, for instance; I
have no concept of an understanding other than my own, one that
must receive its perceptions [Anschauung] by the senses, and
which is occupied in bringing them under rules of the unity of
consciousness. Then the elements of my concept would always lie
in the appearance; I should however by the insufficiency of the
appearance be necessitated to go beyond them to the concept of a
being which neither depends upon appearance, nor is bound up with
them as conditions of its determination. But if I separate
understanding from sensibility to obtain a pure understanding,
then nothing remains but the mere form of thinking without
perception [Anschauung], by which form alone I can know nothing
definite, and consequently no object. For that purpose I should
conceive another understanding, such as would directly perceive
its objects,36 but of which I have not the least notion; because
the human understanding is discursive, and can [not directly
perceive, it can] only know by means of general concepts. And the
very same difficulties arise if we attribute a will to the
Supreme Being; for we have this concept only by drawing it from
our internal experience, and therefore from our dependence for
satisfaction upon objects whose existence we require; and so the
notion rests upon sensibility, which is absolutely incompatible
with the pure concept of the Supreme Being.

Hume's objections to deism are weak, and affect only the
proofs, and not the deistic assertion itself. But as regards
theism, which depends on a stricter determination of the concept
of the Supreme Being which in deism is merely transcendent, they
are very strong, and as this concept is formed, in certain (in
fact in all common) cases irrefutable. Hume always insists, that
by the mere concept of an original being, to which we apply only
ontological predicates (eternity, omnipresence, omnipotence), we
think nothing definite, and that properties which can yield a
concept in concrete must be superadded; that it is not enough to
say, it is Cause, but we must explain the nature of its
causality, for example, that of an understanding and of a will.
He then begins his attacks on the essential point itself, i.e.,
theism, as he; had previously directed his battery only against
the proofs of deism, an attack which is not very dangerous to it
in its consequences. All his dangerous arguments refer to
anthropomorphism, which he holds to be inseparable from theism,
and to make it absurd in itself; but if the former be abandoned,
the latter must vanish with it, and nothing remain but deism, of
which nothing can come, which is of no value, and which cannot
serve as any foundation to religion or morals. If this
anthropomorphism were really unavoidable, no proofs whatever of
the existence of a Supreme Being, even were they all granted,
could determine for us the concept of this Being without
involving us in contradictions.

If we connect with the command to avoid all transcendent
judgments of pure reason, the command (which apparently conflicts
with it) to proceed to concepts that lie beyond the field of its
immanent (empirical) use, we discover that both can subsist
together, but only at the boundary of all lawful use of reason.
For this boundary belongs as well to the field of experience, as
to that of the creations of thought, and we are thereby taught,
as well, bow these so remarkable ideas serve merely for marking
the bounds of human reason. On the one hand they give warning not
boundlessly to extend cognition of experience, as if nothing but
world37 I remained for us to know, and yet, on the other hand,
not to transgress the bounds of experience, and to think of
judging about things beyond them, as things in themselves.

But we stop at this boundary if we limit our judgment merely
to the relation which the world may have to a Being whose very
concept lies beyond all the knowledge which we can attain within
the world. For we then do not attribute to the Supreme Being any
of the properties in themselves, by which we represent objects of
experience, and thereby avoid dogmatic anthropomorphism; but we
attribute them to his relation to the world, and allow ourselves
a symbolical anthropomorphism, which in fact concerns language
only, and not the object itself.

If I say that we are compelled to consider the world, as if
it were the work of a Supreme Understanding and Will, I really
say nothing more, than that a watch, a ship, a regiment, bears
the same relation to the watchmaker, the shipbuilder, the
commanding officer, as the world of sense (or whatever
constitutes the substratum of this complex of appearances) does
to the Unknown, which I do not hereby know as it is in itself,
but as it is for me or in relation to the world, of which I am a

Sect. 58. Such a cognition is one of analogy, and does not
signify (as is commonly understood) an imperfect similarity of
two things, but a perfect similarity of relations between two
quite dissimilar things.38 By means of this analogy, however,
there remains a concept of the Supreme Being sufficiently
determined for us, though we have left out everything that could
determine it absolutely or in itself; for we determine it as
regards the world and as regards ourselves, and more do we not
require. The attacks which Hume makes upon those who would
determine this concept absolutely, by taking the materials for so
doing from themselves and the world, do not affect us; and he
cannot object to us, that we have nothing left if we give up the
objective anthropomorphism of the concept of the Supreme Being.

For let us assume at the outset (as Hume in his dialogues
makes Philo grant Cleanthes), as a necessary hypothesis, the
deistical concept of the First Being, in which this Being is
thought by the mere ontological predicates of substance, of
cause, etc. This must be done, because reason, actuated in the
sensible world by mere conditions, which are themselves always
conditional, cannot otherwise have any satisfaction, and it
therefore can be done without falling into anthropomorphism
(which transfers predicates from the world of sense to a Being
quite distinct from the world), because those predicates are mere
categories, which, though they do not give a determinate concept
of God, yet give a concept not limited to any conditions of
sensibility. Thus nothing can prevent our predicating of this
Being a causality through reason with regard to the world, and
thus passing to theism, without being obliged to attribute to God
in himself this kind of reason, as a property inhering in him.
For as to the former, the only possible way of prosecuting the
use of reason (as regards all possible experience, in complete
harmony with itself) in the world of sense to the highest point,
is to assume a supreme reason as a cause of all the connections
in the world. Such a principle must be quite advantageous to
reason and can hurt it nowhere in its application to nature. As
to the latter, reason is thereby not transferred as a property to
the First Being in himself, but only to his relation to the world
of sense, and so anthropomorphism is entirely avoided. For
nothing is considered here but the cause of the form of reason
which is perceived everywhere in the world, and reason is
attributed to the Supreme Being, so far as it contains the ground
of this form of reason in the world, but according to analogy
only, that is, so far as this expression shows merely the
relation, which the Supreme Cause unknown to us has to the world,
in order to determine everything in it conformably to reason in
the highest degree. We are thereby kept from using reason as an
attribute for the purpose of conceiving God, but instead of
conceiving the world in such a manner as is necessary to have the
greatest possible use of reason according to principle. We
thereby acknowledge that the Supreme Being is quite inscrutable
and even unthinkable in any definite way as to what he is in
himself. We are thereby kept, on the one band, from making a
transcendent use of the concepts which we have of reason as an
efficient cause (by means of the will), in order to determine the
Divine Nature by properties, which are only borrowed from human
nature, and from losing ourselves in gross and extravagant
notions, and on the other hand from deluging the contemplation of
the world with hyperphysical modes of explanation according to
our notions of human reason, which we transfer to God, and so
losing for this contemplation its proper application, according
to which it should be a rational study of mere nature, and not a
presumptuous derivation of its appearances from a Supreme Reason.
The expression suited to our feeble notions is, that we conceive
the world as if it came, as to its existence and internal plan,
from a Supreme Reason, by which notion we both know the
constitution, which belongs to the world itself, yet without
pretending to determine the nature of its cause in itself, and on
the other hand, we transfer the ground of this constitution (of
the form of reason in the world) upon the relation of the Supreme
Cause to the world, without finding the world sufficient by
itself for that purpose.39

Thus the difficulties which seem to oppose theism -disappear
by combining with Hume's principle -- "not to carry the use of
reason dogmatically beyond the field of all possible experience"
-- this other principle, which be quite overlooked: "not to
consider the field of experience as one which bounds itself in
the eye of our reason." The Critique of Pure Reason here points
out the true mean between dogmatism, which Hume combats, and
skepticism, which he would substitute for it-a mean which is not
like other means that we find advisable to determine for
ourselves as it were mechanically (by adopting something from one
side and something from the other), and by which nobody is taught
a better way, but such a one as can be accurately determined on

Sect. 59. At the beginning of this annotation I made use of
the metaphor of a boundary, in order to establish the limits of
reason in regard to its suitable use. The world of sense contains
merely appearances, which are not things in themselves, but the
understanding must assume these latter ones, viz., noumena. In
our reason both are comprised, and the question is, How does
reason proceed to set boundaries to the understanding as regards
both these fields? Experience, which contains all that belongs to
the sensuous world, does not bound itself; it only proceeds in
every case from the conditioned to some other equally conditioned
object. Its boundary must lie quite without it, and this field is
that of the pure beings of the understanding. But this field, so
far as the determination of the nature of these beings is
concerned, is an empty space for us, and if dogmatically-
determined concepts alone are in question, we cannot pass out of
the field of possible experience. But as a boundary itself is
something positive, which belongs as well to that which lies
within, as to the space that lies without the given complex, it
is still an actual positive cognition, which reason only acquires
by enlarging itself to this boundary, yet without attempting to
pass it; because it there finds itself in the presence of an
empty space, in which it can conceive forms of things, but not
things themselves. But the setting of a boundary to the field of
the understanding by something, which is otherwise unknown to it,
is still a cognition which belongs to reason even at this
standpoint, and by which it is neither confined within the
sensible, nor straying without it, but only refers, as befits the
knowledge of a boundary, to the relation between that which lies
without it, and that which is contained within it.

Natural theology is such a concept at the boundary of human
reason, being constrained to look beyond this boundary to the
Idea of a Supreme Being (and, for practical purposes to that of
an intelligible world also), not in order to determine anything
relatively to this pure creation of the understanding, which lies
beyond the world of sense, but in order to guide the use of
reason within it according to principles of the greatest possible
(theoretical as well as practical) unity. For this purpose we
make use of the reference of the world of sense to an independent
reason, as the cause of all its connections. Thereby we do not
purely invent a being, but, as beyond the sensible. world there
must be something that can only be thought by the pure
understanding, we determine that something in this particular
way, though only of course according to analogy.

And thus there remains our original proposition, which is
the resume of the whole Critique: "that reason by all its a
priori principles never teaches us anything more than objects of
possible experience, and even of these nothing more than can be
known in experience." But this limitation does not prevent reason
leading us to the objective boundary of experience, viz., to the
reference to something which is not itself an object of
experience, but is the ground of all experience. Reason does not
however teach us anything concerning the thing in itself: it only
instructs us as regards its own complete and highest use in the
field of possible experience. But this is all that can be
reasonably desired in the present case, and with which we have
cause to be satisfied.

Sect. 60. Thus we have fully exhibited metaphysics as 'it is
actually given in the natural predisposition of human reason, and
in that which constitutes the essential end of its pursuit,
according to its subjective possibility. Though we have found,
that this merely natural use of such a predisposition of our
reason, if no discipline arising only from a scientific critique
bridles and sets limits to it, involves us in transcendent,
either apparently or really conflicting, dialectical syllogisms;
and this fallacious metaphysics is not only unnecessary as
regards the promotion of our knowledge of nature, but even
disadvantageous to it: there yet remains a problem worthy of
solution, which is to find out the natural ends intended by this
disposition to transcendent concepts in our reason, because
everything that lies in nature must be originally intended for
some useful purpose.

Such an inquiry is of a doubtful nature; and I .acknowledge,
that what I can say about it is conjecture only, like every
speculation about the first ends of nature. The question does not
concern the objective validity of metaphysical judgments, but our
natural predisposition to them, and therefore does not belong to
the system of metaphysics but to anthropology.

When I compare all the transcendental Ideas, the totality of
which constitutes the particular problem of natural pure reason,
compelling it to quit the mere contemplation of nature, to
transcend all possible experience, and in this endeavor to
produce the thing (be it knowledge or fiction) called
metaphysics, I think I perceive that the aim of this natural
tendency is, to free our notions from the fetters of experience
and from the limits of the mere contemplation of nature so far as
at least to open to us a field containing mere objects for the
pure understanding, which no sensibility can reach, not indeed
for the purpose of speculatively occupying ourselves with them
(for there we can find no ground to stand on), but because
practical principles, which, without finding some such scope for
their necessary expectation and hope, could not expand to the
universality which reason unavoidably requires from a moral point
of view.

So I find that the Psychological Idea (however little it may
reveal to me the nature of the human soul, which is higher than
all concepts of experience), shows the insufficiency of these
concepts plainly enough, and thereby deters me from materialism,
the psychological notion of which is unfit for any explanation of
nature, and besides confines reason in practical respects. The
Cosmological Ideas, by the obvious insufficiency of all possible
cognition of nature to satisfy reason in its lawful inquiry,
serve in the same manner to keep us from naturalism, which
asserts nature to be sufficient for itself. Finally, all natural
necessity in the sensible world is conditional, as it always
presupposes the dependence of things upon others, and
unconditional necessity must be sought only in the unity of a
cause different from the world of sense. But as the causality of
this cause, in its turn, were it merely nature, could never
render the existence of the contingent (as its consequent)
comprehensible, reason frees itself by means of the Theological
Idea from fatalism, (both as a blind natural necessity in the
coherence of nature itself, without a first principle, and as a
blind causality of this principle itself), and leads to the
concept of a cause possessing freedom, or of a Supreme
Intelligence. Thus the transcendental Ideas serve, if not to
instruct us positively, at least to destroy the rash assertions
of Materialism, of Naturalism, and of Fatalism, and thus to
afford scope for the moral Ideas beyond the field of speculation.
These considerations, I should think, explain in some measure the
natural predisposition of which I spoke.

The practical value, which a merely speculative science may
have, lies without the bounds of this science, and can therefore
be considered as a scholion merely, and like all scholia does not
form part of the science itself. This application however surely
lies within the bounds of philosophy, especially of philosophy
drawn from the pure sources of reason, where its speculative use
in metaphysics must necessarily be at unity with its practical
use in morals. Hence the unavoidable dialectics of pure reason,
considered in metaphysics, as a natural tendency, deserves to be
explained not as an illusion merely, which is to be removed, but
also, if possible, as a natural provision as regards its end,
though this duty, a work of supererogation, cannot justly be
assigned to metaphysics proper.

The solutions of these questions which are treated in the
chapter on the Regulative Use of the Ideas of Pure Reason40
should be considered a second scholion which however has a
greater affinity with the subject of metaphysics. For there
certain rational principles are expounded which determine a
priori the order of nature or rather of the understanding, which
seeks nature's laws through experience. They seem to be
constitutive and legislative with regard to experience, though
they spring from pure reason, which cannot be considered, like
the understanding, as a principle of possible experience. Now
whether or not this harmony rests upon the fact, that just as
nature does not inhere in appearances or in their source (the
sensibility) itself, but only in so far as the latter is in
relation to the understanding, as also a systematic unity in
applying the understanding to bring about an entirety of all
possible experience can only belong to the understanding when in
relation to reason; and whether or not experience is in this way
mediately subordinate to the legislation of reason: may be
discussed by those who desire to trace the nature of reason even
beyond its use in metaphysics, into the general principles of a
history of nature; I have represented this task as important, but
not attempted its solution, in the book itself.41

And thus I conclude the analytical solution of the main
question which I had proposed: How is metaphysics in general
possible? by ascending from the data of its actual use in its
consequences, to the grounds of its possibility.

* * * *


Metaphysics, as a natural disposition of reason, is actual,
but if considered by itself alone (as the analytical solution of
the third principal question showed), dialectical and illusory.
If we think of taking principles from it, and in using them
follow the natural, but on that account not less false, illusion,
we can never produce science, but only a vain dialectical art, in
which one school may outdo another, but none can ever acquire a
just and lasting approbation.

In order that as a science metaphysics may be entitled to
claim not mere fallacious plausibility, but insight and
conviction, a Critique of Reason must itself exhibit the whole
stock of a priori concepts, their division according to their
various sources (Sensibility, Understanding, and Reason),
together with a complete table of them, the analysis of all these
concepts, with all their consequences, especially by means of the
deduction of these concepts, the possibility of synthetical
cognition a priori, the principles of its application and finally
its bounds, all in a complete system. Critique, therefore, and
critique alone, contains in itself the whole well-proved and
well-tested plan, and even all the means required to accomplish
metaphysics, as a science; by other ways and means it is
impossible. The question here therefore is not so much how this
performance is possible, as how to set it going, and induce men
of clear heads to quit their hitherto perverted and fruitless
cultivation for one that will not deceive, and how such a union
for the common end may best be directed.

This much is certain, that whoever has once tasted Critique
will be ever after disgusted with all dogmatical twaddle which be
formerly put up with, because his reason must have something, and
could find nothing better for its support.

Critique stands in the same relation to the common
metaphysics of the schools, as chemistry does to alchemy, or as
astronomy to the astrology of the fortune-teller. I pledge myself
that nobody who has read through and through, and grasped the
principles of, the Critique even in these Prolegomena only, will
ever return to that old and sophistical pseudo-science; but will
rather with a certain delight look forward to metaphysics which
is now indeed in his power, requiring no more preparatory
discoveries, and now at last affording permanent satisfaction to
reason. For here is an advantage upon which, of all possible
sciences, metaphysics alone can with certainty reckon: that it
can be brought to such completion and fixity as to be incapable
of further change, or of any augmentation by new discoveries;
because here reason has the sources of its knowledge in itself,
not in objects and their observation [Anschauung], by which
latter its stock of knowledge cannot be further increased. When
therefore it has exhibited the fundamental laws of its faculty
completely and so definitely as to avoid all misunderstanding,
there remains nothing for pure reason to know a priori, nay,
there is even no ground to raise further questions. The sure
prospect of knowledge so definite and so compact has a peculiar
charm, even though we should set aside all its advantages, of
which I shall hereafter speak.

All false art, all vain wisdom, lasts its time, but finally
destroys itself, and its highest culture is also the epoch of its
decay. That this time is come for metaphysics appears from the
state into which it has fallen among all learned nations, despite
of all the zeal with which other sciences of every kind are
prosecuted. The old arrangement of our university studies still
preserves its shadow; now and then an Academy of Science tempts
men by offering prizes to write essays on it, but it is no longer
numbered among thorough sciences; and let any one judge for
himself how a man of genius, if he were called a great
metaphysician, would receive the compliment, which may be well-
meant, but is scarce envied by anybody.

Yet, though the period of the downfall of all dogmatical
metaphysics has undoubtedly arrived, we are yet far from being
able to say that the period of its regeneration is come by means
of a thorough and complete Critique of Reason. All transitions
from a tendency to its contrary pass through the stage of
indifference, and this moment is the most dangerous for an
author, but, in my opinion, the most favorable for the science.
For, when party spirit has died out by a total dissolution of
former connections, minds are in the best state to listen to
several proposals for an organization according to a new plan.

When I say, that I hope these Prolegomena will excite
investigation in the field of critique and afford a new and
promising object to sustain the general spirit of philosophy,
which seems on its speculative side to want sustenance, I can
imagine beforehand, that every one, whom the thorny paths of my
Critique have tired and put out of humor, will ask me, upon what
I found this hope. My answer is, upon the irresistible law of

That the human mind will ever give up metaphysical
researches is as little to be expected as that we should prefer
to give up breathing altogether, to avoid inhaling impure air.
There will therefore always be metaphysics in the world; nay,
every one, especially every man of reflection, will have it, and
for want of a recognized standard, will shape it for himself
after his own pattern. What has hitherto been called metaphysics,
cannot satisfy any critical mind, but to forego it entirely is
impossible; therefore a Critique of Pure Reason itself must now
be attempted or, if one exists, investigated, and brought to the
full test, because there is no other means of supplying this
pressing want, which is something more than mere thirst for

Ever since I have come to know critique, whenever I finish
reading a book of metaphysical contents, which, by the
preciseness of its notions, by variety, order, and an easy style,
was not only entertaining but also helpful, I cannot help asking,
11 Has this author indeed advanced metaphysics a single step?"
The learned men, whose works have been useful to me in other
respects and always contributed to the culture of my mental
powers, will, I hope, forgive me for saying, that I have never
been able to find either their essays or my own less important
ones (though self-love may recommend them to me) to have advanced
the science of metaphysics in the least, and why?

Here is the very obvious reason: metaphysics did not then
exist as a science, nor can it be gathered piecemeal, but its
germ must be fully preformed in the Critique. But in order to
prevent all misconception, we must remember what has been already
said, that by the analytical treatment of our concepts the
understanding gains indeed a great deal, but the science (of
metaphysics) is thereby not in the least advanced, because these
dissections of concepts are nothing but the materials from which
the intention is to carpenter our science. Let the concepts of
substance and of accident be ever so well dissected and
determined, all this is very well as a preparation for some
future use. But if we cannot prove, that in all which exists the
substance endures, and only the accidents vary, our science is
not the least advanced by all our analyzes.

Metaphysics has hitherto never been able to prove a priori
either this proposition, or that of sufficient reason, still less
any more complex theorem, such as belongs to psychology or
cosmology, or indeed any synthetical proposition. By all its
analyzing therefore nothing is affected, nothing obtained or
forwarded and the science, after all this bustle and noise, still
remains as it was in the days of Aristotle, though far better
preparations were made for it than of old, if the clue to
synthetical cognitions had only been discovered.

If any one thinks himself offended, he is at liberty to
refute my charge by producing a single synthetical proposition
belonging to metaphysics, which he would prove dogmatically a
priori, for until he has actually performed this feat, I shall
not grant that he has truly advanced the science; even should
this proposition be sufficiently confirmed by common experience.
No demand can be more moderate or more equitable, and in the
(inevitably certain) event of its non-performance, no assertion
more just, than that hitherto metaphysics has never existed as a

But there are two things which, in case the challenge be
accepted, I must deprecate: first, trifling about probability and
conjecture, which are suit-d as little to metaphysics, as to
geometry; and secondly, a decision by means of the magic wand of
common sense, which does not convince every one, but which
accommodates itself to personal peculiarities.

For as to the former, nothing can be more absurd, than in
metaphysics, a philosophy from pure reason to think of grounding
our judgments upon probability and conjecture. Everything that is
to be known a priori, is thereby announced as apodictically
certain, and must therefore be proved in this way. We might as
well think of grounding geometry or arithmetic upon conjectures.
As to the doctrine of chances in the latter, it does not contain
probable, but perfectly certain, judgments concerning the degree
of the probability of certain cases, under given uniform
conditions, which, in the sum of all possible cases, infallibly
happen according to the rule, though it is not sufficiently
determined in respect to every single chance. Conjectures (by
means of induction and of analogy) can be suffered in an
empirical science of nature only, yet even there the possibility
at least of what we assume must be quite certain.

The appeal to common sense is even more absurd, when concept
and principles are announced as valid, not in so far as they hold
with regard to experience, but even beyond the conditions of
experience. For what is common sense? It is normal good sense, so
far it judges right. But what is normal good sense? It is the
faculty of the knowledge and use of rules in concreto, as
distinguished from the speculative understanding, which is a
faculty of knowing rules in abstracto. Common sense can hardly
understand the rule, 11 that every event is determined by means
of its cause," and can never comprehend it thus generally. It
therefore demands an example from experience, and when it hears
that this rule means nothing but what it always thought when a
pane was broken or a kitchen-utensil missing, it then understands
the principle and grants it. Common sense therefore is only of
use so far as it can see its rules (though they actually are a
priori) confirmed by experience; consequently to comprehend them
a priori, or independently of experience, belongs to the
speculative understanding, and lies quite beyond the horizon of
common sense. But the province of metaphysics is entirely
confined to the latter kind of knowledge, and it is certainly a
bad index of common sense to appeal to it as a witness, for it
cannot here form any opinion whatever, and men look down upon it
with contempt until they are in difficulties, and can find in
their speculation neither in nor out.

It is a common subterfuge of those false friends of common
sense (who occasionally prize it highly, but usually despise it)
to say, that there must surely be at all events some propositions
which are immediately certain, and of which there is no occasion
to give any proof, or even any account at all, because we
otherwise could never stop inquiring into the grounds of our
judgments. But if we except the principle of contradiction, which
is not sufficient to show the truth of synthetical judgments,
they can never adduce, in proof of this privilege, anything else
indubitable, which they can immediately ascribe to common sense,
except mathematical propositions, such as twice two make four,
between two points there is but one straight line, etc. But these
judgments are radically different from those of metaphysics. For
in mathematics I myself can by thinking construct whatever I
represent to myself as possible by a concept: I add to the first
two the other two, one by one, and myself make the number four,
or I draw in thought from one point to another all manner of
lines, equal as well as unequal; yet I can draw one only, which
is like itself in all its parts. But I cannot, by all my power of
thinking, extract from the concept of a thing the concept of
something else, whose existence is necessarily connected with the
former, but I must call in experience. And though my
understanding furnishes me a priori (yet only in reference to
possible experience) with the concept of such a connection (i.e.,
causation), I cannot exhibit it, like the concepts of
mathematics, by [Anschauung] visualizing them, a priori, and so
show its possibility a priori. This concept, together with the
principles of its application, always requires, if it shall hold
a priori as is requisite in metaphysics -a justification and
deduction of its possibility, because we cannot otherwise know
how far it holds good, and whether it can be used in experience
only or beyond it also.

Therefore in metaphysics, as a speculative science of pure
reason, we can never appeal to common sense, but may do so only
when we are forced to surrender it, and to renounce all purely
speculative cognition, which must always be knowledge, and
consequently when we forego metaphysics itself and its
instruction, for the sake of adopting a rational faith which
alone may be possible for us, and sufficient to our wants,
perhaps even more salutary than knowledge itself. For in this
case the attitude of the question is quite altered. Metaphysics
must be science, not only as a whole, but in all its parts,
otherwise it is nothing; because, as a speculation of pure
reason, it finds a hold only on general opinions. Beyond its
field, however, probability and common sense may be used with
advantage and justly, but on quite special principles, of which
the importance always depends on the reference to practical life.

This is what I hold myself justified in requiring for the
possibility of metaphysics as a science.

* * * *


Since all the ways heretofore taken have failed to attain
the goal, and since without a preceding critique of pure reason
it is not likely ever to be attained, the present essay now
before the public has a fair title to an accurate and careful
investigation, except it be thought more advisable to give up all
pretensions to metaphysics, to which, if men but would
consistently adhere to their purpose, no objection can be made.

If we take the course of things as it is, not as it ought to
be, there are two sorts of judgments: (1) one a judgment which
precedes investigation (in our case one in which the reader from
his own metaphysics pronounces judgment on the Critique of Pure
Reason which was intended to discuss the very possibility of
metaphysics); (2) the other a judgment subsequent to
investigation. In the latter the reader is enabled to waive for
awhile the consequences of the critical researches that may be
repugnant to his formerly adopted metaphysics, and first examines
the grounds whence those consequences are derived. If what common
metaphysics propounds were demonstrably certain, as for instance
the theorems of geometry, the former way of judging would bold
good. For if the consequences of certain principles are repugnant
to established truths, these principles are false and without
further inquiry to be repudiated. But if metaphysics does not
possess a stock of indisputably certain (synthetical)
propositions, and should it even be the case that there are a
number of them, which, though among the most specious, are by
their consequences in mutual collision, and if no sure criterion
of the truth of peculiarly metaphysical (synthetical)
propositions is to be met with in it, then the former way of
judging is not admissible, but the investigation of the
principles of the critique must precede all judgments as to its

On A Specimen Of A Judgment Of The Critique Prior To Its

This judgment is to be found in the Gottingischen gelehrten
Anzeigen, in the supplement to the third division, of January 19,
1782, pages 40 et seq.

When an author who is familiar with the subject of his work
and endeavors to present his independent reflections in its
elaboration, falls into the hands of a reviewer who in his turn,
is keen enough to discern the points on which the worth or
worthlessness of the book rests, who does not cling to words, but
goes to the heart of the subject, sifting and testing more than
the mere principles which the author takes as his point of
departure, the severity of the judgment may indeed displease the
latter, but the public does not care, as it gains thereby; and
the author himself may be contented, as an opportunity of
correcting or explaining his positions is afforded to him at an
early date by the examination of a competent judge, in such a
manner, that if he believes himself fundamentally right, he can
remove in time any stone of offense that might hurt the success
of his work.

I find myself, with my reviewer, in quite another position.
He seems not to see at all the real matter of the investigation
with which (successfully or unsuccessfully) I have been occupied.
It is either impatience at thinking out a lengthy work, or
vexation at a threatened reform of a science in which he believed
he had brought everything to perfection long ago, or, what I am
unwilling to imagine, real narrow-mindedness, that prevents him
from ever carrying his thoughts beyond his school-metaphysics. In
short, he passes impatiently in review a long series of
propositions, by which, without knowing their premises, we can
think nothing, intersperses here and there his censure, the
reason of which the reader understands just as little as the
propositions against which it is directed; and hence [his report]
can neither serve the public nor damage me, in the judgment of
experts. I should, for these reasons, have passed over this
judgment altogether, were it not that it may afford me occasion
for some explanations which may in some cases save the readers of
these Prolegomena from a misconception.

In order to take a position from which my reviewer could
most easily set the whole work in a most unfavorable light,
without venturing to trouble himself with any special
investigation, he begins and ends by saying: "This work is a
system of transcendent (or, as he translates it, of higher)

A glance at this line soon showed me the sort of criticism
that I had to expect, much as though the reviewer were one who
had never seen or heard of geometry, having found a Euclid, and
coming upon various figures in turning over its leaves, were to
say, on being asked his opinion of it: "The work is a text-book
of drawing; the author introduces a peculiar terminology, in
order to give dark, incomprehensible directions, which in the end
teach nothing more than what every one can effect by a fair
natural accuracy of eye, etc."

Let us see, in the meantime, what sort of an idealism it is
that goes through my whole work, although it does not by a long
way constitute the soul of the system.

The dictum of all genuine idealists from the Eleatic school
to Bishop Berkeley, is contained in this formula: "All cognition
through the senses and experience is nothing but sheer illusion,
and only, in the ideas of the pure understanding and reason there
is truth."

The principle that throughout dominates and determines my
Idealism, is on the contrary: "All cognition of things merely
from pure understanding or pure reason is nothing but sheer
illusion, and only in experience is there truth."

But this is directly contrary to idealism proper. How came I
then to use this expression for quite an opposite purpose, and
how came my reviewer to see it everywhere?

The solution of this difficulty rests on something that
could have been very easily understood from the general bearing
of the work, if the reader had only desired to do so. Space and
time, together with all that they contain, are not things nor
qualities in themselves, but belong merely to the appearances of
the latter: up to this point I am one in confession with the
above idealists. But these, and amongst them more particularly
Berkeley, regarded space as a mere empirical presentation that,
like the phenomenon it contains, is only known to us by means of
experience or perception, together with its determinations. I, on
the contrary, prove in the first place, that space (and also
time, which Berkeley did not consider) and all its determinations
a priori, can be known by us, because, no less than time, it
inheres in our sensibility as a pure form before all perception
or experience and makes all intuition of the same, and therefore
all its phenomena, possible. It follows from this, that as truth
rests on universal and necessary laws as its criteria,
experience, according to Berkeley, can have no criteria of truth,
because its phenomena (according to him) have nothing a priori at
their foundation; whence it follows, that they are nothing but
sheer illusion; whereas with us, space and time (in conjunction
with the pure conceptions of the understanding) prescribe their
law to all possible experience a priori, and at the same time
afford the certain criterion for distinguishing truth from
illusion therein.43

My so-called (properly critical) Idealism is of quite a
special character, in that it subverts the ordinary idealism, and
that through it all cognition a priori, even that of geometry,
first receives objective reality, which, without my demonstrated
ideality of space and time, could not be maintained by the most
zealous realists. This being the state of the case, I could have
wished, in order to avoid all misunderstanding, to have named
this conception of mine otherwise, but to alter it altogether was
impossible. It may be permitted me however, in future, as has
been above intimated, to term it the formal, or better still, the
critical Idealism, to distinguish it from the dogmatic Idealism
of Berkeley, and from the skeptical Idealism of Descartes.

Beyond this, I find nothing further remarkable in the
judgment of my book. The reviewer criticizes here and there,
makes sweeping criticisms, a mode prudently chosen, since it does
not betray one's own knowledge or ignorance; a single thorough
criticism in detail, had it touched the main question, as is only
fair, would have exposed, it may be my error, or it may be my
reviewer's measure of insight into this species of research. It
was, moreover, not a badly conceived plan, in order at once to
take from readers (who are accustomed to form their conceptions
of books from newspaper reports) the desire to read the book
itself, to pour out in one breath a number of passages in
succession, torn from their connection, and their grounds of
proof and explanations, and which must necessarily sound
senseless, especially considering how antipathetic they are to
all school-metaphysics; to exhaust the reader's patience ad
nauseam, and then, after having made me acquainted with the
sensible proposition that persistent illusion is truth, to
conclude with the crude paternal moralization: to what end, then,
the quarrel with accepted language, to what end, and whence, the
idealistic distinction? A judgment which seeks all that is
characteristic of my book, first supposed to be metaphysically
heterodox, in a mere innovation of the nomenclature, proves
clearly that my would-be judge has understood nothing of the
subject, and in addition, has not understood himself.44

My reviewer speaks like a man who is conscious of important
and superior insight which he keeps hidden; for I am aware of
nothing recent with respect to metaphysics that could justify his
tone. But he should not withhold his discoveries from the world,
for there are doubtless many who, like myself, have not been able
to find in all the fine things that have for long past been
written in this department, anything that has advanced the
science by so much as a finger-breadth; we find indeed the giving
a new point to definitions, the supplying of lame proofs with new
crutches, the adding to the crazy-quilt of metaphysics fresh
patches or changing its pattern; but all this is not what the
world requires. The world is tired of metaphysical assertions; it
wants the possibility of the science, the sources from which
certainty therein can be derived, and certain criteria by which
it may distinguish the dialectical illusion of pure reason from
truth. To this the critic seems to possess a key, otherwise he
would never have spoken out in such a high tone.

But I am inclined to suspect that no such requirement of the
science has ever entered his thoughts, for in that case he would
have directed his judgment to this point, and even a mistaken
atteriipt in such an important matter, would have won his
respect. If that be the case, we are once more good friends. He
may penetrate as deeply as he likes into metaphysics, without any
one hindering him; only as concerns that which lies outside
metaphysics, its sources, which are to be found in reason, he
cannot form a judgment. That my suspicion is not without
foundation, is proved by the fact that he does not mention a word
about the possibility of synthetic knowledge a priori, the
special problem upon the solution of which the fate of
metaphysics wholly rests, and upon which my Critique (as well as
the present Prolegomena) entirely hinges. The Idealism he
encountered, and which he hung upon,: was only taken up in the
doctrine as the sole means of solving the above problem (although
it received its confirmation on other grounds), and hence he must
have shown either that the above problem does not possess the
importance I attribute to it (even in these Prolegomena), or that
by my conception of appearances, it is either not solved at all,
or can be better solved in another way; but I do not find a word
of this in the criticism. The reviewer, then, understands nothing
of my work, and possibly also nothing of the spirit and essential
nature of metaphysics itself; and it is not, what I would rather
assume, the hurry of a man incensed at the labor of plodding
through so many obstacles, that threw an unfavorable shadow over
the work lying before him, and made its fundamental features

There is a good deal to be done before a learned journal, it
matters not with what care its writers may be selected, can
maintain its otherwise well-merited reputation, in the field of
metaphysics as elsewhere. Other sciences and branches of
knowledge have their standard. Mathematics has it, in itself;
history and theology, in profane or sacred books; natural science
and the art of medicine, in mathematics and experience;
jurisprudence, in law books; and even matters of taste in the
examples of the ancients. But for the judgment of the thing
called metaphysics, the standard has yet to be found. I have made
an attempt to determine it, as well as its use. What is to be
done, then, until it be found, when works of this kind have to be
judged of? If they are of a dogmatic character, -one may do what
one likes; no one will play the master over others here for long,
before some one else appears to deal with him in the same manner.
If, however, they are critical in their character, not indeed
with reference to other works, but to reason itself, so that the
standard of judgment cannot be assumed but has first of all to be
sought for, then, though objection and blame may indeed be
permitted, yet a certain degree of leniency is indispensable,
since the need is common to us all, and the lack of the necessary
insight makes the high-handed attitude of judge unwarranted.

In order, however, to connect my defense with the interest
of the philosophical commonwealth, I propose a test, which must
be decisive as to the mode, whereby all metaphysical
investigations may be directed to their common purpose. This is
nothing more than what formerly mathematicians have done, in
establishing the advantage of their methods by competition. I
challenge my critic to demonstrate, as is only just, on a priori
grounds, in his way, a single really metaphysical principle
asserted by him. Being metaphysical it must be synthetic and
known a priori from conceptions, but it may also be any one of
the most indispensable principles, as for instance, the principle
of the persistence of substance, or of the necessary
determination of events in the world by their causes. If he
cannot do this (silence however is confession), he must admit,
that as metaphysics without apodictic certainty of propositions
of this kind is nothing at all, its possibility or impossibility
must before all things be established in a critique of the pure
reason. Thus he is bound either to confess that my principles in
the Critique are correct, or he must prove their invalidity. But
as I can already foresee, that, confidently as he has hitherto
relied on the certainty of his principles, when it comes to a
strict test he will not find a single one in the whole range of
metaphysics he can bring forward, I will concede to him an
advantageous condition, which can only be expected in such a
competition, and will relieve him of the onus probandi by laying
it on myself.

He finds in these Prolegomena and in my Critique (chapter on
the "Theses and Antitheses Antinomies") eight propositions, of
which two and two contradict one another, but each of which
necessarily belongs to metaphysics, by which it must either be
accepted or rejected (although there is not one that has not in
this time been held by some philosopher). Now he has the liberty
of selecting any one of these eight propositions at his pleasure,
and accepting it without any proof, of which I shall make him a
present, but only one (for waste of time will be just as little
serviceable to him as to me), and then of attacking my proof of
the opposite proposition. If I can save this one, and at the same
time show, that according to principles which every dogmatic
metaphysics must necessarily recognize, the opposite of the
proposition adopted by him can be just as clearly proved, it is
thereby established that metaphysics has an hereditary failing,
not to be explained, much less set aside, until we ascend to its
birth-place, pure reason itself, and thus my Critique must either
be accepted or a better one take its place; it must at least be
studied, which is the only thing I now require. If, on the other
hand, I cannot save my demonstration, then a synthetic
proposition a priori from dogmatic principles is to be reckoned
to the score of my opponent, then also I will deem my impeachment
of ordinary metaphysics as unjust, and pledge myself to recognize
his stricture on my Critique as justified (although this would
not be the consequence by a long way). To this end it would be
necessary, it seems to me, that he should step out of his
incognito. Otherwise I do not see how it could be avoided, that
instead of dealing with one, I should be honored by several
problems coming from anonymous and unqualified opponents.

Proposals As To An Investigation Of The Critique Upon Which A
Judgment May Follow.

I feel obliged to the honored public even for the silence
with which it for a long time favored my Critique, for this
proves at least a postponement of judgment, and some supposition
that in a work, leaving all beaten tracks and striking out on a
new path, in which one cannot at once perhaps so easily find
one's way, something may perchance lie, from which an important
but at present dead branch of human knowledge may derive new life
and productiveness. Hence may have originated a solicitude for
the as yet tender shoot, lest it be destroyed by a hasty
judgment. A test of a judgment, delayed for the above reasons, is
now before my eye in the Gothaischen gelehrten Zeitung, the
thoroughness of which every reader will himself perceive, from
the clear and unperverted presentation of a fragment of one of
the first principles of my work, without taking into
consideration my own suspicious praise.

And now I propose, since an extensive structure cannot be
judged of as a whole from a hurried glance, to test it piece by
piece from its foundations, so thereby the present Prolegomena
may fitly be used as a general outline with which the work itself
may occasionally be compared. This notion, if it were founded on
nothing more than my conceit of importance, such as vanity
commonly attributes to one's own productions, would be immodest
and would deserve to be repudiated with disgust. But now, the
interests of speculative philosophy have arrived at the point of
total extinction, while human reason hangs upon them with
inextinguishable affection, and only after having been
ceaselessly deceived does it vainly attempt to change this into

In our thinking age it is not to be supposed but that many
deserving men would use any good opportunity of working for the
common interest of the more and more enlightened reason, if there
were only some hope of attaining the goal. Mathematics, natural
science, laws, arts, even morality, etc., do not completely fill
the soul; there is always a space left over, reserved for pure
and speculative reason, the vacuity of which prompts us to seek
in vagaries, buffooneries, and mysticism for what seems to be
employment and entertainment, but what actually is mere pastime;
in order to deaden the troublesome voice of reason, which in
accordance with its nature requires something that can satisfy
it, and not merely subserve other ends or the interests of our
inclinations. A consideration, therefore, which is concerned only
with reason as it exists for it itself, has as I may reasonably
suppose a great fascination for every one who has attempted thus
to extend his conceptions, and I may even say a greater than any
other theoretical branch of knowledge, for which he would not
willingly exchange it, because here all other cognitions, and
even purposes, must meet and unite themselves in a whole.45

I offer, therefore, these Prolegomena as a sketch and text-
book for this investigation, and not the work itself. Although I
am even now perfectly satisfied with the latter as far as
contents, order, and mode of presentation, and the care that I
have expended in weighing and testing every sentence before
writing it down, are concerned (for it has taken me years to
satisfy myself fully, not only as regards the whole but in some
cases even as to the sources of one particular proposition); yet
I am not quite satisfied with my exposition in some sections of
the doctrine of elements, as for instance in the deduction of the
conceptions of the Understanding, or in that on the paralogisms
of pure reason, because a certain diffuseness takes away from
their clearness, and in place of them, what is here said in the
Prolegomena respecting these sections, may be made the basis of
the test.

It is the boast of the Germans that where steady and
continuous industry are requisite, they can carry things farther
than other nations. If this opinion be well founded, an
opportunity, a business, presents itself, the successful issue of
which we can scarcely doubt, and in which all thinking men can
equally take part, though they have hitherto been unsuccessful in
accomplishing it and in thus confirming the above good opinion.
But this is chiefly because the science in question is of so
peculiar a kind, that it can be at once brought to completion and
to that enduring state that it will never be able to be brought
in the least degree farther or increased by later discoveries, or
even changed (leaving here out of account adornment by greater
clearness in some places, or additional uses), and this is an
advantage no other science has or can have, because there is none
so fully isolated and independent of others, and which is
concerned with the faculty of cognition pure and simple. And the
present moment seems, moreover, not to be unfavorable to my
expectation, for just now, in Germany, no one seems to know
wherewith to occupy himself, apart from the so-called useful
sciences, so as to pursue not mere play, but a business
possessing an enduring purpose.

To discover the means how the endeavors of the learned may
be united in such a purpose, I must leave to others. In the
meantime, it is my intention to persuade any one merely to follow
my propositions, or even to flatter me with the hope that he will
do so; but attacks, repetitions, limitations, or confirmation,
completion, and extension, as the case may be, should be
appended. If the matter be but investigated from its foundation,
it cannot fail that a system, albeit not my own, shall be
erected, that shall be a possession for future generations for
which they may have reason to be grateful.

It would lead us too far here to show what kind of
metaphysics may be expected, when only the principles of
criticism have been perfected, and how, because the old false
feathers have been pulled out, she need by no means appear poor
and reduced to an insignificant figure, but may be in other
respects richly and respectably adorned. But other and great uses
which would result from such a reform, strike one immediately.
The ordinary metaphysics had its uses, in that it sought out the
elementary conceptions of the pure understanding in order to make
them clear through analysis, and definite by explanation. In this
way it was a training for reason, in whatever direction it might
be turned; but this was all the good it did; service was
subsequently effaced when it favored conceit by venturesome
assertions, sophistry by subtle distinctions and adornment, and
shallowness by the ease with which it decided the most difficult
problems by means of a little school-wisdom, which is only the
more seductive the more it has the choice, on the one hand, of
taking something from the language of science, and on the other
from that of popular discourse, thus being everything to
everybody, but in reality nothing at all. By criticism, however,
a standard is given to our judgment, whereby knowledge may be
with certainty distinguished from pseudo-science, and firmly
founded, being brought into full operation in metaphysics; a mode
of thought extending by degrees its beneficial influence over
every other use of reason, at once infusing into it the true
philosophical spirit. But the service also that metaphysics
performs for theology, by making it independent of the judgment
of dogmatic speculation, thereby assuring it completely against
the attacks of all such opponents, is certainly not to be valued
lightly. For ordinary metaphysics, although it promised the
latter much advantage, could not keep this promise, and moreover,
by summoning speculative dogmatics to its assistance, did nothing
but arm enemies against itself. Mysticism, which can prosper in a
rationalistic age only when it hides itself behind a system of
school-metaphysics, under the protection of which it may venture
to rave with a semblance of rationality, is driven from this, its
last hiding-place, by critical philosophy. Last, but not least,
it cannot be otherwise than important to a teacher of
metaphysics, to be able to say with universal assent, that what
he expounds is Science, and that thereby genuine services will be
rendered to the commonweal.

1 Copyright 1997, James Fieser (, all rights
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2 Says Horace:
" Rusticus expectat, dum defluat amnis, at ille
Labitur et labetur in omne volubilis aevum;
" A rustic fellow waiteth on the shore
For the river to flow away,
But the river flows, and flows on as before,
And it flows forever and aye."
3 Nevertheless Hume called this very destructive science
metaphysics and attached to it great value. "Metaphysics and
morals" he declares "are the most important branches of science;
mathematics and physics are not nearly so important" ["On the
Rise and Progress of Arts and Sciences," Essays, Moral,
Political, and Literary]. But the acute man merely regarded the
negative use arising from the moderation of extravagant claims of
speculative reason, and the complete settlement of the many
endless and troublesome controversies that mislead mankind. He
overlooked the positive injury which results, if reason be
deprived of its most important prospects, which can alone supply
to the will the highest aim for all its endeavor.
4 [The term Anschauung here used means sense-perception. It is
that which is given to the senses and apprehended Immediately, as
an object is seen by merely looking at it. The translation
intuiition, though etymologically correct, is misleading. In the

present passage the term is not used in its technical
significance but means " practical experience."-Ed.]
5 [The term apodictic is borrowed by Kant from Aristotle who uses
it in the sense of "certain beyond dispute." The word is derived
from [Greek] (= I show) and is contrasted to dialectic
propositions, i. e., such statements " admit of controversy. --
6 It is unavoidable that as knowledge advances, certain
expressions which have become classical, after having been used
since the infancy: of science, will be found inadequate and
unsuitable, and a newer and more appropriate application of the
terms will give rise to confusion. . [This is the case with the
term " analytical."] The analytical method, so far as it is
opposed to the synthetical, is very different from that which
constitutes the essence of analytical propositions: it signifies
only that we start from what is sought, as if it were given, and
ascend to the only conditions under which it is possible. In this
method we often use nothing but synthetical propositions, as in
mathematical analysis, and it were better to term it the
regressive method, in contradistinction to the synthetic or
progressive. A principal part of Logic too is distinguished by
the name of Analytics, which here signifies the logic of truth in
contrast to Dialectics, without considering whether the
cognitions belonging to it are analytical or synthetical.
7 [This whole paragraph (Sect. 9) will be better understood when
compared with Remark I., following this section. - Ed.]
8 [Empirical judgments (emfiirische Urtheile) are either mere
statements of fact, viz.. records of a perception, or statements
of a natural law, implying a causal connection between two facts.
The former Kant calls" judgments of perception"
(Wahrnehmungsurtheile), the latter "judgments of experience "
9 I freely grant that these examples do not represent such
judgments of perception as ever could become judgments of
experience, even though a concept of the understanding were
superadded, because they refer merely to feeling, which everybody
knows to be merely subjective, and which of course can never be
attributed to the object, and consequently never become
objective. I only wished to give here an example of a judgment
that is merely subjectively valid, containing no ground for
universal validity, and thereby for a relation to the object. An
example of the judgments of perception, which become judgments of
experience by superadded concepts of the understanding, will be
given in the next note.
10 As an easier example, we may take the following: " When the
sun shines on the stone, it grows warm." This judgment, however
often I and others may have perceived it, is a mere judgment of
perception, and contains no necessity; perceptions are only
usually conjoined in this manner. But if I say, "The sun warms
the stone," I add to the perception a concept of the
understanding, viz., that of cause, which connects with the
concept of sunshine that of heat as a necessary consequence, and
the synthetical judgment becomes of necessity universally valid,
viz., objective, and is converted from a perception into
11 This name seems preferable to the term particularia, which is
used for these judgments in logic. For the latter implies the
idea that they are not universal. But when I start from unity (in
single judgments) and so proceed to universality, I must not
[even indirectly and negatively] imply any reference to
universality. I think plurality merely without universality, and
not the exception from universality. This is necessary, if
logical considerations shall form the basis of the pure concepts
of the understanding. However, there is no need of making changes
in logic.
12 But how does this proposition, 11 that judgments of experience
contain necessity in the synthesis of perceptions," agree with my
statement so often before inculcated, that "experience as
cognition a posteriori can afford contingent judgments only?
"When I say that experience teaches me something, I mean only the
perception that lies in experience,-for example, that heat always
follows the shining of the sun on a stone; consequently the
proposition of experience is always so far accidental. That this
heat necessarily follows the shining of the sun is contained
indeed in the judgment of experience (by means of the concept of
cause), yet is a fact not learned by experience; for conversely,
experience is first of all generated by this addition of the
concept of the understanding (of cause) to perception. How
perception attains this addition may be seen by referring in the
Critique itself to the section on the Transcendental faculty of
Judgment Lviz-, in the first edition, Vex dem Schematismxs der
Taxes Verstandsbegrirel.
13 [Kant uses the term physiological in its etymological meaning
as "pertaining to the science of physics," i.e., nature in
general, not as we use the term now as "pertaining to the
functions of the living body." Accordingly it has been translated
"physical." -- Ed.]
14 The three following paragraphs will hardly be understood
unless reference be made to what the Citique itself says on the
subject of the Principles; they will, however, be of service in
giving a general view of the Principles, and in fixing the
attention of the main points.
15 [Kant uses here the equivocal term Wechsetwirkung. --Ed.]
16 Heat and light are in a small space just as large as to degree
as in a large one; in like manner the internal representations,
pain, consciousness in general, whether they last a short or a
long time, need not vary as to the degree. Hence the quantity is
here in a point and in a moment just as great as in any space or
time however great. Degrees are therefore capable of increase,
but not in intuition, rather in mere sensation (or the quantity
of the degree of an intuition). Hence they can only be estimated
quantitatively by the relation of 1 to 0, viz, by their
capability of decreasing by infinite intermediate degrees to
disappearance, or of increasing from naught through infinite
gradations to a determinate sensation in a certain time.
Quantitas qualitatis est gradus [i.e., the degrees of quality
must be measured by equality.]
17 We speak of the "intelligible world," not (as the usual
expression is) "intellectual world." For cognitions are
intellectual through the understanding, and refer to our world of
sense also; but objects, so far as they can be represented merely
by the understanding, and to which none of our sensible
intuitions can refer, are termed " intelligible." But as some
possible intuition must correspond to every object, we would have
to assume an understanding that intuits things immediately; but
of such we have not the least notion, nor have we of the things
of the understanding [Verstandes wasen], to which it should be
18 Crusius alone thought of a compromise: that a Spirit, who can
neither err nor deceive, implanted these laws in us originally.
But since false principles often intrude themselves, as indeed
the very system of this man shows in not a few examples, we are
involved ill difficulties as to the use of such a principle in
the absence of sure criteria to distinguish the genuine origin
from the spurious as we never can know certainly what the Spirit
of truth or the father of lies may have instilled into us.
19 The definition of nature is given in the beginning of the
Second Part of the " Transcendental Problem," in Sect. 14.
20 1. Substantia, 2. Qualitas 3, Quamtitas, 4. Relatio, 5. Actio,
6. Passio, 7. Quando, 8. Ubi, 9. Situs, 10. Habitus.
21 Oppositum, Prius, Simul, Motus, Habere.
22 See the two tables in the chapters Von den Paralogismen der
reinen Verunft and the first division of the Antinomy of Pure
Reason, System der kosmologischen Ideen.
23 On the table of the categories many neat observations may be
made, for instance (1) that the third arises from the first and
the second joined in one concept (2) that in those of Quantity
and of Quality there is merely a progress from unity to totality
or from something to nothing (for this purpose the categories of
Quality must stand thus: reality, limitation, total negation),
without correlata or opposita, whereas those of Relation and of
Modality have them; (3) that, as in Logic categorical judgments
are the basis of all others, so the category of Substance is the
basis of all concepts of actual things; (4) that as Modality in
the judgment is not a particular predicate, so by the modal
concepts a determination is not superadded to things, etc., etc.
Such observations are of great use. If we besides enumerate all
the predicables, which we can find pretty completely in any good
ontology (for example, Baumgarten's), and arrange them in classes
under the categories, in which operation we must not neglect to
add as complete a dissection of all these concepts as possible,
there will then arise a merely analytical part of metaphysics,
which does not contain a single synthetical proposition. which
might precede the second (the synthetical), and would by its
precision and completeness be not only useful, but, in virtue of
its system, be even to some extent elegant.
24 See Critique of Pure Reason, Von der Amphibolie der
25 If we can say, that a science is actual at least in the idea
of all men, as soon as it appears that the problems which lead to
it are proposed to everybody by the nature of human reason, and
that therefore many (though faulty) endeavors are unavoidably
made in its behalf, then we are bound to Fay that metaphysics is
subjectively (and indeed necessarily) actual, and therefore we
justly ask, how is it (objectively) possible.
26 In disjunctive judgments we consider all possibility as
divided in respect to a particular concept. By the ontological
principle of the universal determination of a thing in general, I
understand the principle that either the one or the other of all
possible contradictory predicates must be assigned to any object.
This is at the same time the principle of all disjunctive
judgments, constituting the foundation of our conception of
possibility, and in it the possibility of every object in general
is considered as determined. This may serve as a slight
explanation of the above proposition: that the activity of reason
in disjunctive syllogisms is formally the same as that by which
it fashions the idea of a universal conception of all reality,
containing in itself that which is positive in all contradictory
27 See Critique of Pure Reason, Von ded Paralogismen der reinen
28 Were the representation of the apperception (the Ego) a
concept, by which anything could be thought, it could be used as
a predicate 'of other things or contain predicates in itself. But
it is nothing more than the feeling of an existence without the
least definite conception and is only the representation of that
to which all thinking stands in relation (relative accidentis).
29 Cf. Critique, Von den Analogien der Erfahrung.
30 It is indeed very remarkable how carelessly metaphysicians
have always passed over the principle of the permanents of
substances without ever attempting a proof of it; doubtless
because they found themselves abandoned by all proofs as soon as
they began to deal with the concept of substance. Common sense,
which felt distinctly that without this presupposition no union
of perceptions in experience is possible, supplied the want by a
postulate. From experience itself it never could derive such a
principle, partly because substances cannot be so traced in all
their alterations and dissolutions, that the matter can always be
found undiminished, partly because the principle contains
Necessity. which is always the sign of an a priori principle.
People then boldly applied this postulate to the concept of soul
as a substance, and concluded a necessary continuance of the soul
after the death of man (especially as the simplicity of this
substance, which is interred from the indivisibility of
consciousness, secured it from destruction by dissolution). Had
they found the genuine source of this principles discovery which
requires deeper researches than they were ever inclined to make -
- they would have seen, that the law of the permanence of
substances has place for the purposes of experience only, and
hence can hold good of things so far as they are to be known and
conjoined with others in experience, but never independently of
all possible experience, and consequently cannot hold good of the
soul after death.
31 Cf. Critique, Die antinomie der reinen Vernunft.
32 I therefore would be pleased to have the critical reader to
devote to this antinomy of pure reason his chief attention,
because nature itself seems to have established it with a view to
stagger reason in its daring pretensions, and to force it to
self-examination. For every proof, which I have given, as well of
the thesis as of the antithesis, I undertake to be responsible,
and thereby to show the certainty of the inevitable antinomy of
reason. When the reader is brought by this curious phenomenon to
fall back upon the proof of the presumption upon which it rests,
he will feet himself obliged to investigate the ultimate
foundation of all the cognition of pure reason with me more
33 The idea of freedom occurs only in the relation of the
intellectual, as cause, to the appearance, as effect. Hence we
cannot attribute freedom to matter in regard to the incessant
action by which it fills its space. though this action takes
place from an internal principle. We dan likewise find no notion
of freedom suitable to purely rational beings, for instance, to
God, so far as his action is immanent. For his action, though
independent of external determining causes, is determined in his
eternal reason, that is, in the divine nature. It is only, if
something, is to start by an action, and so the effect occurs in
the sequence of time, or in the world of sense (e.g., the
beginning of the world), that we can put the question, whether
the causality of the cause must in its turn have been started, or
whether the cause can originate an effect without its causality
itself beginning. In the former case the concept of this
causality is a concept of natural necessity, in the latter, that
of freedom. From this the reader will see. that, as I explained
freedom to be the faculty of starting an event spontaneously, I
have exactly hit the notion which is the problem of metaphysics.
34 Cf. Critique, the chapter on "Transcendental Ideals."
35 Herr Platner in his Aphorisms acutely says (Sects. 728, 729),
"If reason be a criterion, no concept, which is incomprehensible
to human reason, can be possible. Incomprehensibility has place
in what is actual only. Here incomprehensibility arises from the
insufficiency of the acquired ideas." It sounds paradoxical, but
is otherwise not strange to say, that in nature there is much
incomprehensible (e.g., the faculty of generation) but if we
mount still higher, and even go beyond nature, everything again
becomes comprehensible; for we then quit entirely the objects,
which can be given us, and occupy ourselves merely about ideas,
in which occupation we can easily comprehend the law that reason
prescribes by them to the understanding for its use in
experience, because the law is the reason's own production.
36 Der die Gegenstande anschaute.
37 [The use of the word "world" without article, though odd,
seems to be the correct reading, but it may be a mere misprint. -
- Ed.]
38 There is, e.g., an analogy between the juridical relation of
human actions and the mechanical relation of motive powers. I
never can do anything to an. other man without giving him a right
to do the same to me on the same conditions; just as no mass can
act with its motive power on another mass without thereby
occasioning the other to react equally against it. Here right and
motive power are quite dissimilar things, but in their relation
there is complete similarity. By means of such an analogy I can
obtain a notion of the relation of things which absolutely are
unknown to me. For instance, as the promotion of the welfare of
children (= a) is to the love of parents (= b), so the welfare of
the human species (= c) is to that unknown [quantity which is] in
God (= x), which we call love; not as if it had the least
similarity to any human inclination, but because we can suppose
its relation to the world to be similar to that which things of
the world bear one another. But the concept of relation in this
case is a mere category, viz., the concept of cause, which has
nothing to do with sensibility.
39 I may say, that the causality of the Supreme Cause holds the
same place with regard to the world that human reason does with
regard to its works of art. Here the nature of the Supreme Cause
itself remains unknown to me: I only compare its effects (the
order of the world) which I know, and their conformity to reason,
to the effects of human reason which I also know; and hence I
term the former reason, without attributing to it on that account
what I understand in man by this term, or attaching to it
anything else known to me, as its property.
40 Critique Pure Reason, II., chap. 3, section 7.
41 Throughout in the Critique I never lost sight of the plan not
to neglect anything, were it ever so recondite, that could render
the inquiry into the nature of pure reason complete. Everybody
may afterwards carry his researches as far as he pleases, when he
has been merely shown what yet remains to be done. It is this a
duty which must reasonably be expected of him who has made it his
business to survey the whole field, in order to consign it to
others for future cultivation and allotment. And to this branch
both the scholia belong, which will hardly recommend themselves
by their dryness to amateurs, and hence are added here for
connoisseurs only.
42 By no means "higher." High towers, and metaphysically-great
man resembling them, round both of which there is commonly much
wind, are not for me. My place is the fruitful bathos, the
bottom-land, of experience; and the word transcendental, the
meaning of which is so often explained by me but not once grasped
by my reviewer (so carelessly has he regarded everything), does
not signify something passing beyond all experience, but some.
thing that indeed precedes it a priori, but that is intended
simply to make cognition of experience possible. If these
conceptions overstep experience, their employment is termed
transcendent, a word which must be distinguished from
transcendental, the latter being limited to the immanent use,
that is, to experience. All misunderstandings of this kind have
been sufficiently guarded against in the work itself, but my
reviewer found his advantage in misunderstanding me.
43 Idealism proper always has a mystical tendency, and can have
no other, but mine is solely designed for the purpose of
comprehending the possibility of our cognition a priori as to
objects of experience, which is a problem never hitherto solved
or even suggested. In this way all mystical idealism falls to the
ground, for (as may be seen already in Plato) it inferred from
our cognitions a priori (even from those of geometry) another
intuition different from that of the senses (namely, an
intellectual intuition), because it never occurred to any one
that the senses themselves might intuit a priori.
44 The reviewer often fights with his own shadow. When I oppose
the truth of experience to dream, he never thinks that I am here
speaking simply of the well-known somnio objective sumto of the
Wolffian philosophy, which is merely formal, and with which the
distinction between sleeping and waking is in no way concerned,
and in a transcendental philosophy indeed can have no place. For
the rest, he calls my deduction of the categories and table of
the principles of the understanding," common well-known axioms of
logic and ontology, expressed in an idealistic manner." The
reader need only consult these Prolegomena upon this point, to
convince himself that a more miserable and historically
incorrect, judgment, could hardly be made.
45 [Kant rewrote these sections in the second edition of the

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