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The Critique of Pure Reason by Immanuel Kant

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by Immanuel Kant

translated by J. M. D. Meiklejohn


Human reason, in one sphere of its cognition, is called upon to
consider questions, which it cannot decline, as they are presented
by its own nature, but which it cannot answer, as they transcend every
faculty of the mind.

It falls into this difficulty without any fault of its own. It
begins with principles, which cannot be dispensed with in the field
of experience, and the truth and sufficiency of which are, at the same
time, insured by experience. With these principles it rises, in
obedience to the laws of its own nature, to ever higher and more
remote conditions. But it quickly discovers that, in this way, its
labours must remain ever incomplete, because new questions never cease
to present themselves; and thus it finds itself compelled to have
recourse to principles which transcend the region of experience, while
they are regarded by common sense without distrust. It thus falls into
confusion and contradictions, from which it conjectures the presence
of latent errors, which, however, it is unable to discover, because
the principles it employs, transcending the limits of experience,
cannot be tested by that criterion. The arena of these endless
contests is called Metaphysic.

Time was, when she was the queen of all the sciences; and, if we
take the will for the deed, she certainly deserves, so far as
regards the high importance of her object-matter, this title of
honour. Now, it is the fashion of the time to heap contempt and
scorn upon her; and the matron mourns, forlorn and forsaken, like

Modo maxima rerum,
Tot generis, natisque potens...
Nunc trahor exul, inops.
-- Ovid, Metamorphoses. xiii

At first, her government, under the administration of the
dogmatists, was an absolute despotism. But, as the legislative
continued to show traces of the ancient barbaric rule, her empire
gradually broke up, and intestine wars introduced the reign of
anarchy; while the sceptics, like nomadic tribes, who hate a permanent
habitation and settled mode of living, attacked from time to time
those who had organized themselves into civil communities. But their
number was, very happily, small; and thus they could not entirely
put a stop to the exertions of those who persisted in raising new
edifices, although on no settled or uniform plan. In recent times
the hope dawned upon us of seeing those disputes settled, and the
legitimacy of her claims established by a kind of physiology of the
human understanding--that of the celebrated Locke. But it was found
that--although it was affirmed that this so-called queen could not
refer her descent to any higher source than that of common experience,
a circumstance which necessarily brought suspicion on her claims--as
this genealogy was incorrect, she persisted in the advancement of
her claims to sovereignty. Thus metaphysics necessarily fell back into
the antiquated and rotten constitution of dogmatism, and again
became obnoxious to the contempt from which efforts had been made to
save it. At present, as all methods, according to the general
persuasion, have been tried in vain, there reigns nought but weariness
and complete indifferentism--the mother of chaos and night in the
scientific world, but at the same time the source of, or at least
the prelude to, the re-creation and reinstallation of a science,
when it has fallen into confusion, obscurity, and disuse from ill
directed effort.

For it is in reality vain to profess indifference in regard to
such inquiries, the object of which cannot be indifferent to humanity.
Besides, these pretended indifferentists, however much they may try
to disguise themselves by the assumption of a popular style and by
changes on the language of the schools, unavoidably fall into
metaphysical declarations and propositions, which they profess to
regard with so much contempt. At the same time, this indifference,
which has arisen in the world of science, and which relates to that
kind of knowledge which we should wish to see destroyed the last, is
a phenomenon that well deserves our attention and reflection. It is
plainly not the effect of the levity, but of the matured judgement*
of the age, which refuses to be any longer entertained with illusory
knowledge, It is, in fact, a call to reason, again to undertake the
most laborious of all tasks--that of self-examination, and to
establish a tribunal, which may secure it in its well-grounded claims,
while it pronounces against all baseless assumptions and
pretensions, not in an arbitrary manner, but according to its own
eternal and unchangeable laws. This tribunal is nothing less than
the critical investigation of pure reason.

[*Footnote: We very often hear complaints of the shallowness of the
present age, and of the decay of profound science. But I do not think
that those which rest upon a secure foundation, such as mathematics,
physical science, etc., in the least deserve this reproach, but that
they rather maintain their ancient fame, and in the latter case,
indeed, far surpass it. The same would be the case with the other
kinds of cognition, if their principles were but firmly established.
In the absence of this security, indifference, doubt, and finally,
severe criticism are rather signs of a profound habit of thought.
Our age is the age of criticism, to which everything must be
subjected. The sacredness of religion, and the authority of
legislation, are by many regarded as grounds of exemption from the
examination of this tribunal. But, if they on they are exempted,
they become the subjects of just suspicion, and cannot lay claim to
sincere respect, which reason accords only to that which has stood
the test of a free and public examination.]

I do not mean by this a criticism of books and systems, but a
critical inquiry into the faculty of reason, with reference to the
cognitions to which it strives to attain without the aid of
experience; in other words, the solution of the question regarding
the possibility or impossibility of metaphysics, and the determination
of the origin, as well as of the extent and limits of this science.
All this must be done on the basis of principles.

This path--the only one now remaining--has been entered upon by
me; and I flatter myself that I have, in this way, discovered the
cause of--and consequently the mode of removing--all the errors
which have hitherto set reason at variance with itself, in the
sphere of non-empirical thought. I have not returned an evasive answer
to the questions of reason, by alleging the inability and limitation
of the faculties of the mind; I have, on the contrary, examined them
completely in the light of principles, and, after having discovered
the cause of the doubts and contradictions into which reason fell,
have solved them to its perfect satisfaction. It is true, these
questions have not been solved as dogmatism, in its vain fancies and
desires, had expected; for it can only be satisfied by the exercise
of magical arts, and of these I have no knowledge. But neither do these
come within the compass of our mental powers; and it was the duty of
philosophy to destroy the illusions which had their origin in
misconceptions, whatever darling hopes and valued expectations may
be ruined by its explanations. My chief aim in this work has been
thoroughness; and I make bold to say that there is not a single
metaphysical problem that does not find its solution, or at least
the key to its solution, here. Pure reason is a perfect unity; and
therefore, if the principle presented by it prove to be insufficient
for the solution of even a single one of those questions to which
the very nature of reason gives birth, we must reject it, as we could
not be perfectly certain of its sufficiency in the case of the others.

While I say this, I think I see upon the countenance of the reader
signs of dissatisfaction mingled with contempt, when he hears
declarations which sound so boastful and extravagant; and yet they
are beyond comparison more moderate than those advanced by the commonest
author of the commonest philosophical programme, in which the
dogmatist professes to demonstrate the simple nature of the soul, or
the necessity of a primal being. Such a dogmatist promises to extend
human knowledge beyond the limits of possible experience; while I
humbly confess that this is completely beyond my power. Instead of
any such attempt, I confine myself to the examination of reason alone
and its pure thought; and I do not need to seek far for the
sum-total of its cognition, because it has its seat in my own mind.
Besides, common logic presents me with a complete and systematic
catalogue of all the simple operations of reason; and it is my task
to answer the question how far reason can go, without the material
presented and the aid furnished by experience.

So much for the completeness and thoroughness necessary in the
execution of the present task. The aims set before us are not
arbitrarily proposed, but are imposed upon us by the nature of
cognition itself.

The above remarks relate to the matter of our critical inquiry. As
regards the form, there are two indispensable conditions, which any
one who undertakes so difficult a task as that of a critique of pure
reason, is bound to fulfil. These conditions are certitude and

As regards certitude, I have fully convinced myself that, in this
sphere of thought, opinion is perfectly inadmissible, and that
everything which bears the least semblance of an hypothesis must be
excluded, as of no value in such discussions. For it is a necessary
condition of every cognition that is to be established upon a priori
grounds that it shall be held to be absolutely necessary; much more
is this the case with an attempt to determine all pure a priori
cognition, and to furnish the standard--and consequently an example--
of all apodeictic (philosophical) certitude. Whether I have
succeeded in what I professed to do, it is for the reader to
determine; it is the author's business merely to adduce grounds and
reasons, without determining what influence these ought to have on
the mind of his judges. But, lest anything he may have said may become
the innocent cause of doubt in their minds, or tend to weaken the effect
which his arguments might otherwise produce--he may be allowed to
point out those passages which may occasion mistrust or difficulty,
although these do not concern the main purpose of the present work.
He does this solely with the view of removing from the mind of the
reader any doubts which might affect his judgement of the work as a
whole, and in regard to its ultimate aim.

I know no investigations more necessary for a full insight into
the nature of the faculty which we call understanding, and at the same
time for the determination of the rules and limits of its use, than
those undertaken in the second chapter of the "Transcendental
Analytic," under the title of "Deduction of the Pure Conceptions of
the Understanding"; and they have also cost me by far the greatest
labour--labour which, I hope, will not remain uncompensated. The
view there taken, which goes somewhat deeply into the subject, has
two sides, The one relates to the objects of the pure understanding,
and is intended to demonstrate and to render comprehensible the
objective validity of its a priori conceptions; and it forms for
this reason an essential part of the Critique. The other considers
the pure understanding itself, its possibility and its powers of
cognition--that is, from a subjective point of view; and, although
this exposition is of great importance, it does not belong essentially
to the main purpose of the work, because the grand question is what
and how much can reason and understanding, apart from experience,
cognize, and not, how is the faculty of thought itself possible? As
the latter is an, inquiry into the cause of a given effect, and has
thus in it some semblance of an hypothesis (although, as I shall
show on another occasion, this is really not the fact), it would
seem that, in the present instance, I had allowed myself to enounce
a mere opinion, and that the reader must therefore be at liberty to
hold a different opinion. But I beg to remind him that, if my
subjective deduction does not produce in his mind the conviction of
its certitude at which I aimed, the objective deduction, with which
alone the present work is properly concerned, is in every respect

As regards clearness, the reader has a right to demand, in the first
place, discursive or logical clearness, that is, on the basis of
conceptions, and, secondly, intuitive or aesthetic clearness, by means
of intuitions, that is, by examples or other modes of illustration
in concreto. I have done what I could for the first kind of
intelligibility. This was essential to my purpose; and it thus
became the accidental cause of my inability to do complete justice
to the second requirement. I have been almost always at a loss, during
the progress of this work, how to settle this question. Examples and
illustrations always appeared to me necessary, and, in the first
sketch of the Critique, naturally fell into their proper places. But
I very soon became aware of the magnitude of my task, and the numerous
problems with which I should be engaged; and, as I perceived that this
critical investigation would, even if delivered in the driest
scholastic manner, be far from being brief, I found it unadvisable
to enlarge it still more with examples and explanations, which are
necessary only from a popular point of view. I was induced to take
this course from the consideration also that the present work is not
intended for popular use, that those devoted to science do not require
such helps, although they are always acceptable, and that they would
have materially interfered with my present purpose. Abbe Terrasson
remarks with great justice that, if we estimate the size of a work,
not from the number of its pages, but from the time which we require
to make ourselves master of it, it may be said of many a book that
it would be much shorter, if it were not so short. On the other
hand, as regards the comprehensibility of a system of speculative
cognition, connected under a single principle, we may say with equal
justice: many a book would have been much clearer, if it had not
been intended to be so very clear. For explanations and examples,
and other helps to intelligibility, aid us in the comprehension of
parts, but they distract the attention, dissipate the mental power
of the reader, and stand in the way of his forming a clear
conception of the whole; as he cannot attain soon enough to a survey
of the system, and the colouring and embellishments bestowed upon it
prevent his observing its articulation or organization--which is the
most important consideration with him, when he comes to judge of its
unity and stability.

The reader must naturally have a strong inducement to co-operate
with the present author, if he has formed the intention of erecting
a complete and solid edifice of metaphysical science, according to
the plan now laid before him. Metaphysics, as here represented, is
the only science which admits of completion--and with little labour,
if it is united, in a short time; so that nothing will be left to future
generations except the task of illustrating and applying it
didactically. For this science is nothing more than the inventory of
all that is given us by pure reason, systematically arranged.
Nothing can escape our notice; for what reason produces from itself
cannot lie concealed, but must be brought to the light by reason
itself, so soon as we have discovered the common principle of the
ideas we seek. The perfect unity of this kind of cognitions, which
are based upon pure conceptions, and uninfluenced by any empirical
element, or any peculiar intuition leading to determinate
experience, renders this completeness not only practicable, but also

Tecum habita, et noris quam sit tibi curta supellex.
-- Persius. Satirae iv. 52.

Such a system of pure speculative reason I hope to be able to
publish under the title of Metaphysic of Nature*. The content of this
work (which will not be half so long) will be very much richer than
that of the present Critique, which has to discover the sources of
this cognition and expose the conditions of its possibility, and at
the same time to clear and level a fit foundation for the scientific
edifice. In the present work, I look for the patient hearing and the
impartiality of a judge; in the other, for the good-will and
assistance of a co-labourer. For, however complete the list of
principles for this system may be in the Critique, the correctness
of the system requires that no deduced conceptions should be absent.
These cannot be presented a priori, but must be gradually
discovered; and, while the synthesis of conceptions has been fully
exhausted in the Critique, it is necessary that, in the proposed work,
the same should be the case with their analysis. But this will be
rather an amusement than a labour.

[*Footnote: In contradistinction to the Metaphysic of Ethics. This
work was never published.]


Whether the treatment of that portion of our knowledge which lies
within the province of pure reason advances with that undeviating
certainty which characterizes the progress of science, we shall be
at no loss to determine. If we find those who are engaged in
metaphysical pursuits, unable to come to an understanding as to the
method which they ought to follow; if we find them, after the most
elaborate preparations, invariably brought to a stand before the
goal is reached, and compelled to retrace their steps and strike
into fresh paths, we may then feel quite sure that they are far from
having attained to the certainty of scientific progress and may rather
be said to be merely groping about in the dark. In these circumstances
we shall render an important service to reason if we succeed in simply
indicating the path along which it must travel, in order to arrive
at any results--even if it should be found necessary to abandon many
of those aims which, without reflection, have been proposed for its

That logic has advanced in this sure course, even from the
earliest times, is apparent from the fact that, since Aristotle, it
has been unable to advance a step and, thus, to all appearance has
reached its completion. For, if some of the moderns have thought to
enlarge its domain by introducing psychological discussions on the
mental faculties, such as imagination and wit, metaphysical,
discussions on the origin of knowledge and the different kinds of
certitude, according to the difference of the objects (idealism,
scepticism, and so on), or anthropological discussions on
prejudices, their causes and remedies: this attempt, on the part of
these authors, only shows their ignorance of the peculiar nature of
logical science. We do not enlarge but disfigure the sciences when
we lose sight of their respective limits and allow them to run into
one another. Now logic is enclosed within limits which admit of
perfectly clear definition; it is a science which has for its object
nothing but the exposition and proof of the formal laws of all
thought, whether it be a priori or empirical, whatever be its origin
or its object, and whatever the difficulties--natural or accidental--
which it encounters in the human mind.

The early success of logic must be attributed exclusively to the
narrowness of its field, in which abstraction may, or rather must,
be made of all the objects of cognition with their characteristic
distinctions, and in which the understanding has only to deal with
itself and with its own forms. It is, obviously, a much more difficult
task for reason to strike into the sure path of science, where it
has to deal not simply with itself, but with objects external to
itself. Hence, logic is properly only a propaedeutic--forms, as it
were, the vestibule of the sciences; and while it is necessary to
enable us to form a correct judgement with regard to the various
branches of knowledge, still the acquisition of real, substantive
knowledge is to be sought only in the sciences properly so called,
that is, in the objective sciences.

Now these sciences, if they can be termed rational at all, must
contain elements of a priori cognition, and this cognition may stand
in a twofold relation to its object. Either it may have to determine
the conception of the object--which must be supplied extraneously,
or it may have to establish its reality. The former is theoretical,
the latter practical, rational cognition. In both, the pure or a
priori element must be treated first, and must be carefully
distinguished from that which is supplied from other sources. Any
other method can only lead to irremediable confusion.

Mathematics and physics are the two theoretical sciences which
have to determine their objects a priori. The former is purely a
priori, the latter is partially so, but is also dependent on other
sources of cognition.

In the earliest times of which history affords us any record,
mathematics had already entered on the sure course of science, among
that wonderful nation, the Greeks. Still it is not to be supposed that
it was as easy for this science to strike into, or rather to construct
for itself, that royal road, as it was for logic, in which reason
has only to deal with itself. On the contrary, I believe that it
must have remained long--chiefly among the Egyptians--in the stage
of blind groping after its true aims and destination, and that it
was revolutionized by the happy idea of one man, who struck out and
determined for all time the path which this science must follow, and
which admits of an indefinite advancement. The history of this
intellectual revolution--much more important in its results than the
discovery of the passage round the celebrated Cape of Good Hope--and
of its author, has not been preserved. But Diogenes Laertius, in
naming the supposed discoverer of some of the simplest elements of
geometrical demonstration--elements which, according to the ordinary
opinion, do not even require to be proved--makes it apparent that
the change introduced by the first indication of this new path, must
have seemed of the utmost importance to the mathematicians of that
age, and it has thus been secured against the chance of oblivion. A
new light must have flashed on the mind of the first man (Thales, or
whatever may have been his name) who demonstrated the properties of
the isosceles triangle. For he found that it was not sufficient to
meditate on the figure, as it lay before his eyes, or the conception
of it, as it existed in his mind, and thus endeavour to get at the
knowledge of its properties, but that it was necessary to produce
these properties, as it were, by a positive a priori construction;
and that, in order to arrive with certainty at a priori cognition,
he must not attribute to the object any other properties than those
which necessarily followed from that which he had himself, in accordance
with his conception, placed in the object.

A much longer period elapsed before physics entered on the highway
of science. For it is only about a century and a half since the wise
Bacon gave a new direction to physical studies, or rather--as others
were already on the right track--imparted fresh vigour to the
pursuit of this new direction. Here, too, as in the case of
mathematics, we find evidence of a rapid intellectual revolution. In
the remarks which follow I shall confine myself to the empirical
side of natural science.

When Galilei experimented with balls of a definite weight on the
inclined plane, when Torricelli caused the air to sustain a weight
which he had calculated beforehand to be equal to that of a definite
column of water, or when Stahl, at a later period, converted metals
into lime, and reconverted lime into metal, by the addition and
subtraction of certain elements; [Footnote: I do not here follow
with exactness the history of the experimental method, of which,
indeed, the first steps are involved in some obscurity.] a light broke
upon all natural philosophers. They learned that reason only perceives
that which it produces after its own design; that it must not be content
to follow, as it were, in the leading-strings of nature, but must proceed
in advance with principles of judgement according to unvarying laws,
and compel nature to reply its questions. For accidental observations,
made according to no preconceived plan, cannot be united under a
necessary law. But it is this that reason seeks for and requires. It
is only the principles of reason which can give to concordant
phenomena the validity of laws, and it is only when experiment is
directed by these rational principles that it can have any real
utility. Reason must approach nature with the view, indeed, of
receiving information from it, not, however, in the character of a
pupil, who listens to all that his master chooses to tell him, but
in that of a judge, who compels the witnesses to reply to those
questions which he himself thinks fit to propose. To this single
idea must the revolution be ascribed, by which, after groping in the
dark for so many centuries, natural science was at length conducted
into the path of certain progress.

We come now to metaphysics, a purely speculative science, which
occupies a completely isolated position and is entirely independent
of the teachings of experience. It deals with mere conceptions--not,
like mathematics, with conceptions applied to intuition--and in it,
reason is the pupil of itself alone. It is the oldest of the sciences,
and would still survive, even if all the rest were swallowed up in
the abyss of an all-destroying barbarism. But it has not yet had the
good fortune to attain to the sure scientific method. This will be
apparent; if we apply the tests which we proposed at the outset. We
find that reason perpetually comes to a stand, when it attempts to
gain a priori the perception even of those laws which the most
common experience confirms. We find it compelled to retrace its
steps in innumerable instances, and to abandon the path on which it
had entered, because this does not lead to the desired result. We
find, too, that those who are engaged in metaphysical pursuits are
far from being able to agree among themselves, but that, on the
contrary, this science appears to furnish an arena specially adapted
for the display of skill or the exercise of strength in mock-contests--
a field in which no combatant ever yet succeeded in gaining an inch
of ground, in which, at least, no victory was ever yet crowned with
permanent possession.

This leads us to inquire why it is that, in metaphysics, the sure
path of science has not hitherto been found. Shall we suppose that
it is impossible to discover it? Why then should nature have visited
our reason with restless aspirations after it, as if it were one of
our weightiest concerns? Nay, more, how little cause should we have
to place confidence in our reason, if it abandons us in a matter about
which, most of all, we desire to know the truth--and not only so,
but even allures us to the pursuit of vain phantoms, only to betray
us in the end? Or, if the path has only hitherto been missed, what
indications do we possess to guide us in a renewed investigation,
and to enable us to hope for greater success than has fallen to the
lot of our predecessors?

It appears to me that the examples of mathematics and natural
philosophy, which, as we have seen, were brought into their present
condition by a sudden revolution, are sufficiently remarkable to fix
our attention on the essential circumstances of the change which has
proved so advantageous to them, and to induce us to make the
experiment of imitating them, so far as the analogy which, as rational
sciences, they bear to metaphysics may permit. It has hitherto been
assumed that our cognition must conform to the objects; but all
attempts to ascertain anything about these objects a priori, by
means of conceptions, and thus to extend the range of our knowledge,
have been rendered abortive by this assumption. Let us then make the
experiment whether we may not be more successful in metaphysics, if
we assume that the objects must conform to our cognition. This appears,
at all events, to accord better with the possibility of our gaining
the end we have in view, that is to say, of arriving at the
cognition of objects a priori, of determining something with respect
to these objects, before they are given to us. We here propose to do
just what Copernicus did in attempting to explain the celestial
movements. When he found that he could make no progress by assuming
that all the heavenly bodies revolved round the spectator, he reversed
the process, and tried the experiment of assuming that the spectator
revolved, while the stars remained at rest. We may make the same
experiment with regard to the intuition of objects. If the intuition
must conform to the nature of the objects, I do not see how we can
know anything of them a priori. If, on the other hand, the object
conforms to the nature of our faculty of intuition, I can then
easily conceive the possibility of such an a priori knowledge. Now
as I cannot rest in the mere intuitions, but--if they are to become
cognitions--must refer them, as representations, to something, as
object, and must determine the latter by means of the former, here
again there are two courses open to me. Either, first, I may assume
that the conceptions, by which I effect this determination, conform
to the object--and in this case I am reduced to the same perplexity
as before; or secondly, I may assume that the objects, or, which is
the same thing, that experience, in which alone as given objects they
are cognized, conform to my conceptions--and then I am at no loss
how to proceed. For experience itself is a mode of cognition which
requires understanding. Before objects, are given to me, that is, a
priori, I must presuppose in myself laws of the understanding which
are expressed in conceptions a priori. To these conceptions, then,
all the objects of experience must necessarily conform. Now there are
objects which reason thinks, and that necessarily, but which cannot
be given in experience, or, at least, cannot be given so as reason
thinks them. The attempt to think these objects will hereafter furnish
an excellent test of the new method of thought which we have adopted,
and which is based on the principle that we only cognize in things
a priori that which we ourselves place in them.*

[*Footnote: This method, accordingly, which we have borrowed from the
natural philosopher, consists in seeking for the elements of pure reason
in that which admits of confirmation or refutation by experiment. Now
the propositions of pure reason, especially when they transcend the
limits of possible experience, do not admit of our making any experiment
with their objects, as in natural science. Hence, with regard to those
conceptions and principles which we assume a priori, our only course
ill be to view them from two different sides. We must regard one and
the same conception, on the one hand, in relation to experience as
an object of the senses and of the understanding, on the other hand,
in relation to reason, isolated and transcending the limits of
experience, as an object of mere thought. Now if we find that, when
we regard things from this double point of view, the result is in harmony
with the principle of pure reason, but that, when we regard them
from a single point of view, reason is involved in self-contradiction,
then the experiment will establish the correctness of this

This attempt succeeds as well as we could desire, and promises to
metaphysics, in its first part--that is, where it is occupied with
conceptions a priori, of which the corresponding objects may be
given in experience--the certain course of science. For by this new
method we are enabled perfectly to explain the possibility of a priori
cognition, and, what is more, to demonstrate satisfactorily the laws
which lie a priori at the foundation of nature, as the sum of the
objects of experience--neither of which was possible according to
the procedure hitherto followed. But from this deduction of the
faculty of a priori cognition in the first part of metaphysics, we
derive a surprising result, and one which, to all appearance,
militates against the great end of metaphysics, as treated in the
second part. For we come to the conclusion that our faculty of
cognition is unable to transcend the limits of possible experience;
and yet this is precisely the most essential object of this science.
The estimate of our rational cognition a priori at which we arrive
is that it has only to do with phenomena, and that things in
themselves, while possessing a real existence, lie beyond its
sphere. Here we are enabled to put the justice of this estimate to
the test. For that which of necessity impels us to transcend the limits
of experience and of all phenomena is the unconditioned, which reason
absolutely requires in things as they are in themselves, in order to
complete the series of conditions. Now, if it appears that when, on
the one hand, we assume that our cognition conforms to its objects
as things in themselves, the unconditioned cannot be thought without
contradiction, and that when, on the other hand, we assume that our
representation of things as they are given to us, does not conform
to these things as they are in themselves, but that these objects,
as phenomena, conform to our mode of representation, the contradiction
disappears: we shall then be convinced of the truth of that which we
began by assuming for the sake of experiment; we may look upon it as
established that the unconditioned does not lie in things as we know
them, or as they are given to us, but in things as they are in
themselves, beyond the range of our cognition.*

[*Footnote: This experiment of pure reason has a great similarity to
that of the chemists, which they term the experiment of reduction,
or, more usually, the synthetic process. The analysis of the metaphysician
separates pure cognition a priori into two heterogeneous elements,
viz., the cognition of things as phenomena, and of things in
themselves. Dialectic combines these again into harmony with the
necessary rational idea of the unconditioned, and finds that this
harmony never results except through the above distinction, which
is, therefore, concluded to be just.]

But, after we have thus denied the power of speculative reason to
make any progress in the sphere of the supersensible, it still remains
for our consideration whether data do not exist in practical cognition
which may enable us to determine the transcendent conception of the
unconditioned, to rise beyond the limits of all possible experience
from a practical point of view, and thus to satisfy the great ends
of metaphysics. Speculative reason has thus, at least, made room for
such an extension of our knowledge: and, if it must leave this space
vacant, still it does not rob us of the liberty to fill it up, if we
can, by means of practical data--nay, it even challenges us to make
the attempt.*

[*Footnote: So the central laws of the movements of the heavenly bodies
established the truth of that which Copernicus, first, assumed only
as a hypothesis, and, at the same time, brought to light that invisible
force (Newtonian attraction) which holds the universe together. The
latter would have remained forever undiscovered, if Copernicus had
not ventured on the experiment--contrary to the senses but still just--
of looking for the observed movements not in the heavenly bodies,
but in the spectator. In this Preface I treat the new metaphysical
method as a hypothesis with the view of rendering apparent the first
attempts at such a change of method, which are always hypothetical.
But in the Critique itself it will be demonstrated, not
hypothetically, but apodeictically, from the nature of our
representations of space and time, and from the elementary conceptions
of the understanding.]

This attempt to introduce a complete revolution in the procedure
of metaphysics, after the example of the geometricians and natural
philosophers, constitutes the aim of the Critique of Pure
Speculative Reason. It is a treatise on the method to be followed,
not a system of the science itself. But, at the same time, it marks
out and defines both the external boundaries and the internal structure
of this science. For pure speculative reason has this peculiarity,
that, in choosing the various objects of thought, it is able to define
the limits of its own faculties, and even to give a complete
enumeration of the possible modes of proposing problems to itself,
and thus to sketch out the entire system of metaphysics. For, on the
one hand, in cognition a priori, nothing must be attributed to the
objects but what the thinking subject derives from itself; and, on
the other hand, reason is, in regard to the principles of cognition,
a perfectly distinct, independent unity, in which, as in an organized
body, every member exists for the sake of the others, and all for the
sake of each, so that no principle can be viewed, with safety, in one
relationship, unless it is, at the same time, viewed in relation to
the total use of pure reason. Hence, too, metaphysics has this
singular advantage--an advantage which falls to the lot of no other
science which has to do with objects--that, if once it is conducted
into the sure path of science, by means of this criticism, it can then
take in the whole sphere of its cognitions, and can thus complete
its work, and leave it for the use of posterity, as a capital which
can never receive fresh accessions. For metaphysics has to deal only
with principles and with the limitations of its own employment as
determined by these principles. To this perfection it is, therefore,
bound, as the fundamental science, to attain, and to it the maxim
may justly be applied:

Nil actum reputans, si quid superesset agendum.

But, it will be asked, what kind of a treasure is this that we
propose to bequeath to posterity? What is the real value of this
system of metaphysics, purified by criticism, and thereby reduced to
a permanent condition? A cursory view of the present work will lead
to the supposition that its use is merely negative, that it only serves
to warn us against venturing, with speculative reason, beyond the
limits of experience. This is, in fact, its primary use. But this,
at once, assumes a positive value, when we observe that the principles
with which speculative reason endeavours to transcend its limits
lead inevitably, not to the extension, but to the contraction of the
use of reason, inasmuch as they threaten to extend the limits of
sensibility, which is their proper sphere, over the entire realm of
thought and, thus, to supplant the pure (practical) use of reason.
So far, then, as this criticism is occupied in confining speculative
reason within its proper bounds, it is only negative; but, inasmuch
as it thereby, at the same time, removes an obstacle which impedes
and even threatens to destroy the use of practical reason, it possesses
a positive and very important value. In order to admit this, we have
only to be convinced that there is an absolutely necessary use of pure
reason--the moral use--in which it inevitably transcends the limits
of sensibility, without the aid of speculation, requiring only to be
insured against the effects of a speculation which would involve it
in contradiction with itself. To deny the positive advantage of the
service which this criticism renders us would be as absurd as to
maintain that the system of police is productive of no positive
benefit, since its main business is to prevent the violence which
citizen has to apprehend from citizen, that so each may pursue his
vocation in peace and security. That space and time are only forms
of sensible intuition, and hence are only conditions of the
existence of things as phenomena; that, moreover, we have no
conceptions of the understanding, and, consequently, no elements for
the cognition of things, except in so far as a corresponding intuition
can be given to these conceptions; that, accordingly, we can have no
cognition of an object, as a thing in itself, but only as an object
of sensible intuition, that is, as phenomenon--all this is proved in
the analytical part of the Critique; and from this the limitation of
all possible speculative cognition to the mere objects of
experience, follows as a necessary result. At the same time, it must
be carefully borne in mind that, while we surrender the power of
cognizing, we still reserve the power of thinking objects, as things
in themselves.* For, otherwise, we should require to affirm the
existence of an appearance, without something that appears--which
would be absurd. Now let us suppose, for a moment, that we had not
undertaken this criticism and, accordingly, had not drawn the
necessary distinction between things as objects of experience and
things as they are in themselves. The principle of causality, and,
by consequence, the mechanism of nature as determined by causality,
would then have absolute validity in relation to all things as
efficient causes. I should then be unable to assert, with regard to
one and the same being, e.g., the human soul, that its will is free,
and yet, at the same time, subject to natural necessity, that is,
not free, without falling into a palpable contradiction, for in both
propositions I should take the soul in the same signification, as a
thing in general, as a thing in itself--as, without previous
criticism, I could not but take it. Suppose now, on the other hand,
that we have undertaken this criticism, and have learnt that an object
may be taken in two senses, first, as a phenomenon, secondly, as a
thing in itself; and that, according to the deduction of the
conceptions of the understanding, the principle of causality has
reference only to things in the first sense. We then see how it does
not involve any contradiction to assert, on the one hand, that the
will, in the phenomenal sphere--in visible action--is necessarily
obedient to the law of nature, and, in so far, not free; and, on the
other hand, that, as belonging to a thing in itself, it is not subject
to that law, and, accordingly, is free. Now, it is true that I cannot,
by means of speculative reason, and still less by empirical
observation, cognize my soul as a thing in itself and consequently,
cannot cognize liberty as the property of a being to which I ascribe
effects in the world of sense. For, to do so, I must cognize this
being as existing, and yet not in time, which--since I cannot
support my conception by any intuition--is impossible. At the same
time, while I cannot cognize, I can quite well think freedom, that
is to say, my representation of it involves at least no contradiction,
if we bear in mind the critical distinction of the two modes of
representation (the sensible and the intellectual) and the
consequent limitation of the conceptions of the pure understanding
and of the principles which flow from them. Suppose now that morality
necessarily presupposed liberty, in the strictest sense, as a property
of our will; suppose that reason contained certain practical, original
principles a priori, which were absolutely impossible without this
presupposition; and suppose, at the same time, that speculative reason
had proved that liberty was incapable of being thought at all. It
would then follow that the moral presupposition must give way to the
speculative affirmation, the opposite of which involves an obvious
contradiction, and that liberty and, with it, morality must yield to
the mechanism of nature; for the negation of morality involves no
contradiction, except on the presupposition of liberty. Now morality
does not require the speculative cognition of liberty; it is enough
that I can think it, that its conception involves no contradiction,
that it does not interfere with the mechanism of nature. But even this
requirement we could not satisfy, if we had not learnt the twofold
sense in which things may be taken; and it is only in this way that
the doctrine of morality and the doctrine of nature are confined
within their proper limits. For this result, then, we are indebted
to a criticism which warns us of our unavoidable ignorance with regard
to things in themselves, and establishes the necessary limitation of
our theoretical cognition to mere phenomena.

[*Footnote: In order to cognize an object, I must be able to prove
its possibility, either from its reality as attested by experience,
or a priori, by means of reason. But I can think what I please, provided
only I do not contradict myself; that is, provided my conception is
a possible thought, though I may be unable to answer for the existence
of a corresponding object in the sum of possibilities. But something
more is required before I can attribute to such a conception objective
validity, that is real possibility--the other possibility being merely
logical. We are not, however, confined to theoretical sources of
cognition for the means of satisfying this additional requirement,
but may derive them from practical sources.]

The positive value of the critical principles of pure reason in
relation to the conception of God and of the simple nature of the
soul, admits of a similar exemplification; but on this point I shall
not dwell. I cannot even make the assumption--as the practical
interests of morality require--of God, freedom, and immortality, if
I do not deprive speculative reason of its pretensions to transcendent
insight. For to arrive at these, it must make use of principles which,
in fact, extend only to the objects of possible experience, and
which cannot be applied to objects beyond this sphere without
converting them into phenomena, and thus rendering the practical
extension of pure reason impossible. I must, therefore, abolish
knowledge, to make room for belief. The dogmatism of metaphysics, that
is, the presumption that it is possible to advance in metaphysics
without previous criticism, is the true source of the unbelief (always
dogmatic) which militates against morality.

Thus, while it may be no very difficult task to bequeath a legacy to
posterity, in the shape of a system of metaphysics constructed in
accordance with the Critique of Pure Reason, still the value of such
a bequest is not to be depreciated. It will render an important
service to reason, by substituting the certainty of scientific
method for that random groping after results without the guidance of
principles, which has hitherto characterized the pursuit of
metaphysical studies. It will render an important service to the
inquiring mind of youth, by leading the student to apply his powers
to the cultivation of genuine science, instead of wasting them, as
at present, on speculations which can never lead to any result, or
on the idle attempt to invent new ideas and opinions. But, above all,
it will confer an inestimable benefit on morality and religion, by
showing that all the objections urged against them may be silenced
for ever by the Socratic method, that is to say, by proving the ignorance
of the objector. For, as the world has never been, and, no doubt, never
will be without a system of metaphysics of one kind or another, it
is the highest and weightiest concern of philosophy to render it
powerless for harm, by closing up the sources of error.

This important change in the field of the sciences, this loss of its
fancied possessions, to which speculative reason must submit, does
not prove in any way detrimental to the general interests of humanity.
The advantages which the world has derived from the teachings of pure
reason are not at all impaired. The loss falls, in its whole extent,
on the monopoly of the schools, but does not in the slightest degree
touch the interests of mankind. I appeal to the most obstinate
dogmatist, whether the proof of the continued existence of the soul
after death, derived from the simplicity of its substance; of the
freedom of the will in opposition to the general mechanism of
nature, drawn from the subtle but impotent distinction of subjective
and objective practical necessity; or of the existence of God, deduced
from the conception of an ens realissimum--the contingency of the
changeable, and the necessity of a prime mover, has ever been able
to pass beyond the limits of the schools, to penetrate the public
mind, or to exercise the slightest influence on its convictions. It
must be admitted that this has not been the case and that, owing to
the unfitness of the common understanding for such subtle
speculations, it can never be expected to take place. On the contrary,
it is plain that the hope of a future life arises from the feeling,
which exists in the breast of every man, that the temporal is
inadequate to meet and satisfy the demands of his nature. In like
manner, it cannot be doubted that the clear exhibition of duties in
opposition to all the claims of inclination, gives rise to the
consciousness of freedom, and that the glorious order, beauty, and
providential care, everywhere displayed in nature, give rise to the
belief in a wise and great Author of the Universe. Such is the genesis
of these general convictions of mankind, so far as they depend on
rational grounds; and this public property not only remains
undisturbed, but is even raised to greater importance, by the doctrine
that the schools have no right to arrogate to themselves a more
profound insight into a matter of general human concernment than
that to which the great mass of men, ever held by us in the highest
estimation, can without difficulty attain, and that the schools
should, therefore, confine themselves to the elaboration of these
universally comprehensible and, from a moral point of view, amply
satisfactory proofs. The change, therefore, affects only the
arrogant pretensions of the schools, which would gladly retain, in
their own exclusive possession, the key to the truths which they
impart to the public.

Quod mecum nescit, solus vult scire videri.

At the same time it does not deprive the speculative philosopher of
his just title to be the sole depositor of a science which benefits
the public without its knowledge--I mean, the Critique of Pure Reason.
This can never become popular and, indeed, has no occasion to be so;
for finespun arguments in favour of useful truths make just as
little impression on the public mind as the equally subtle
objections brought against these truths. On the other hand, since both
inevitably force themselves on every man who rises to the height of
speculation, it becomes the manifest duty of the schools to enter upon
a thorough investigation of the rights of speculative reason and,
thus, to prevent the scandal which metaphysical controversies are
sure, sooner or later, to cause even to the masses. It is only by
criticism that metaphysicians (and, as such, theologians too) can be
saved from these controversies and from the consequent perversion of
their doctrines. Criticism alone can strike a blow at the root of
materialism, fatalism, atheism, free-thinking, fanaticism, and
superstition, which are universally injurious--as well as of
idealism and scepticism, which are dangerous to the schools, but can
scarcely pass over to the public. If governments think proper to
interfere with the affairs of the learned, it would be more consistent
with a wise regard for the interests of science, as well as for
those of society, to favour a criticism of this kind, by which alone
the labours of reason can be established on a firm basis, than to
support the ridiculous despotism of the schools, which raise a loud
cry of danger to the public over the destruction of cobwebs, of
which the public has never taken any notice, and the loss of which,
therefore, it can never feel.

This critical science is not opposed to the dogmatic procedure of
reason in pure cognition; for pure cognition must always be
dogmatic, that is, must rest on strict demonstration from sure
principles a priori--but to dogmatism, that is, to the presumption
that it is possible to make any progress with a pure cognition,
derived from (philosophical) conceptions, according to the
principles which reason has long been in the habit of employing--
without first inquiring in what way and by what right reason has
come into the possession of these principles. Dogmatism is thus the
dogmatic procedure of pure reason without previous criticism of its
own powers, and in opposing this procedure, we must not be supposed
to lend any countenance to that loquacious shallowness which arrogates
to itself the name of popularity, nor yet to scepticism, which makes
short work with the whole science of metaphysics. On the contrary,
our criticism is the necessary preparation for a thoroughly scientific
system of metaphysics which must perform its task entirely a priori,
to the complete satisfaction of speculative reason, and must,
therefore, be treated, not popularly, but scholastically. In
carrying out the plan which the Critique prescribes, that is, in the
future system of metaphysics, we must have recourse to the strict
method of the celebrated Wolf, the greatest of all dogmatic
philosophers. He was the first to point out the necessity of
establishing fixed principles, of clearly defining our conceptions,
and of subjecting our demonstrations to the most severe scrutiny,
instead of rashly jumping at conclusions. The example which he set
served to awaken that spirit of profound and thorough investigation
which is not yet extinct in Germany. He would have been peculiarly
well fitted to give a truly scientific character to metaphysical
studies, had it occurred to him to prepare the field by a criticism
of the organum, that is, of pure reason itself. That he failed to
perceive the necessity of such a procedure must be ascribed to the
dogmatic mode of thought which characterized his age, and on this
point the philosophers of his time, as well as of all previous
times, have nothing to reproach each other with. Those who reject at
once the method of Wolf, and of the Critique of Pure Reason, can
have no other aim but to shake off the fetters of science, to change
labour into sport, certainty into opinion, and philosophy into

In this second edition, I have endeavoured, as far as possible, to
remove the difficulties and obscurity which, without fault of mine
perhaps, have given rise to many misconceptions even among acute
thinkers. In the propositions themselves, and in the demonstrations
by which they are supported, as well as in the form and the entire
plan of the work, I have found nothing to alter; which must be attributed
partly to the long examination to which I had subjected the whole
before offering it to the public and partly to the nature of the case.
For pure speculative reason is an organic structure in which there
is nothing isolated or independent, but every Single part is essential
to all the rest; and hence, the slightest imperfection, whether defect
or positive error, could not fail to betray itself in use. I
venture, further, to hope, that this system will maintain the same
unalterable character for the future. I am led to entertain this
confidence, not by vanity, but by the evidence which the equality of
the result affords, when we proceed, first, from the simplest elements
up to the complete whole of pure reason and, and then, backwards
from the whole to each part. We find that the attempt to make the
slightest alteration, in any part, leads inevitably to contradictions,
not merely in this system, but in human reason itself. At the same
time, there is still much room for improvement in the exposition of
the doctrines contained in this work. In the present edition, I have
endeavoured to remove misapprehensions of the aesthetical part,
especially with regard to the conception of time; to clear away the
obscurity which has been found in the deduction of the conceptions
of the understanding; to supply the supposed want of sufficient
evidence in the demonstration of the principles of the pure
understanding; and, lastly, to obviate the misunderstanding of the
paralogisms which immediately precede the rational psychology.
Beyond this point--the end of the second main division of the
"Transcendental Dialectic"--I have not extended my alterations,*
partly from want of time, and partly because I am not aware that any
portion of the remainder has given rise to misconceptions among
intelligent and impartial critics, whom I do not here mention with
that praise which is their due, but who will find that their
suggestions have been attended to in the work itself.

[*Footnote: The only addition, properly so called--and that only in
the method of proof--which I have made in the present edition, consists
of a new refutation of psychological idealism, and a strict
demonstration--the only one possible, as I believe--of the objective
reality of external intuition. However harmless idealism may be
considered--although in reality it is not so--in regard to the
essential ends of metaphysics, it must still remain a scandal to
philosophy and to the general human reason to be obliged to assume,
as an article of mere belief, the existence of things external to
ourselves (from which, yet, we derive the whole material of
cognition for the internal sense), and not to be able to oppose a
satisfactory proof to any one who may call it in question. As there
is some obscurity of expression in the demonstration as it stands in
the text, I propose to alter the passage in question as follows:
"But this permanent cannot be an intuition in me. For all the
determining grounds of my existence which can be found in me are
representations and, as such, do themselves require a permanent,
distinct from them, which may determine my existence in relation to
their changes, that is, my existence in time, wherein they change."
It may, probably, be urged in opposition to this proof that, after
all, I am only conscious immediately of that which is in me, that is,
of my representation of external things, and that, consequently, it
must always remain uncertain whether anything corresponding to this
representation does or does not exist externally to me. But I am
conscious, through internal experience, of my existence in time
(consequently, also, of the determinability of the former in the
latter), and that is more than the simple consciousness of my
representation. It is, in fact, the same as the empirical
consciousness of my existence, which can only be determined in
relation to something, which, while connected with my existence, is
external to me. This consciousness of my existence in time is,
therefore, identical with the consciousness of a relation to something
external to me, and it is, therefore, experience, not fiction,
sense, not imagination, which inseparably connects the external with
my internal sense. For the external sense is, in itself, the
relation of intuition to something real, external to me; and the
reality of this something, as opposed to the mere imagination of it,
rests solely on its inseparable connection with internal experience
as the condition of its possibility. If with the intellectual
consciousness of my existence, in the representation: I am, which
accompanies all my judgements, and all the operations of my
understanding, I could, at the same time, connect a determination of
my existence by intellectual intuition, then the consciousness of a
relation to something external to me would not be necessary. But the
internal intuition in which alone my existence can be determined,
though preceded by that purely intellectual consciousness, is itself
sensible and attached to the condition of time. Hence this
determination of my existence, and consequently my internal experience
itself, must depend on something permanent which is not in me, which
can be, therefore, only in something external to me, to which I must
look upon myself as being related. Thus the reality of the external
sense is necessarily connected with that of the internal, in order
to the possibility of experience in general; that is, I am just as
certainly conscious that there are things external to me related to
my sense as I am that I myself exist as determined in time. But in
order to ascertain to what given intuitions objects, external me,
really correspond, in other words, what intuitions belong to the
external sense and not to imagination, I must have recourse, in
every particular case, to those rules according to which experience
in general (even internal experience) is distinguished from
imagination, and which are always based on the proposition that
there really is an external experience. We may add the remark that
the representation of something permanent in existence, is not the
same thing as the permanent representation; for a representation may
be very variable and changing--as all our representations, even that
of matter, are--and yet refer to something permanent, which must,
therefore, be distinct from all my representations and external to
me, the existence of which is necessarily included in the determination
of my own existence, and with it constitutes one experience--an
experience which would not even be possible internally, if it were
not also at the same time, in part, external. To the question How?
we are no more able to reply, than we are, in general, to think the
stationary in time, the coexistence of which with the variable,
produces the conception of change.]

In attempting to render the exposition of my views as intelligible
as possible, I have been compelled to leave out or abridge various
passages which were not essential to the completeness of the work,
but which many readers might consider useful in other respects, and
might be unwilling to miss. This trifling loss, which could not be
avoided without swelling the book beyond due limits, may be
supplied, at the pleasure of the reader, by a comparison with the
first edition, and will, I hope, be more than compensated for by the
greater clearness of the exposition as it now stands.

I have observed, with pleasure and thankfulness, in the pages of
various reviews and treatises, that the spirit of profound and
thorough investigation is not extinct in Germany, though it may have
been overborne and silenced for a time by the fashionable tone of a
licence in thinking, which gives itself the airs of genius, and that
the difficulties which beset the paths of criticism have not prevented
energetic and acute thinkers from making themselves masters of the
science of pure reason to which these paths conduct--a science which
is not popular, but scholastic in its character, and which alone can
hope for a lasting existence or possess an abiding value. To these
deserving men, who so happily combine profundity of view with a talent
for lucid exposition--a talent which I myself am not conscious of
possessing--I leave the task of removing any obscurity which may still
adhere to the statement of my doctrines. For, in this case, the danger
is not that of being refuted, but of being misunderstood. For my own
part, I must henceforward abstain from controversy, although I shall
carefully attend to all suggestions, whether from friends or
adversaries, which may be of use in the future elaboration of the
system of this propaedeutic. As, during these labours, I have advanced
pretty far in years this month I reach my sixty-fourth year--it will
be necessary for me to economize time, if I am to carry out my plan
of elaborating the metaphysics of nature as well as of morals, in
confirmation of the correctness of the principles established in
this Critique of Pure Reason, both speculative and practical; and I
must, therefore, leave the task of clearing up the obscurities of
the present work--inevitable, perhaps, at the outset--as well as,
the defence of the whole, to those deserving men, who have made my
system their own. A philosophical system cannot come forward armed
at all points like a mathematical treatise, and hence it may be
quite possible to take objection to particular passages, while the
organic structure of the system, considered as a unity, has no
danger to apprehend. But few possess the ability, and still fewer
the inclination, to take a comprehensive view of a new system. By
confining the view to particular passages, taking these out of their
connection and comparing them with one another, it is easy to pick
out apparent contradictions, especially in a work written with any
freedom of style. These contradictions place the work in an unfavourable
light in the eyes of those who rely on the judgement of others, but
are easily reconciled by those who have mastered the idea of the whole.
If a theory possesses stability in itself, the action and reaction
which seemed at first to threaten its existence serve only, in the
course of time, to smooth down any superficial roughness or
inequality, and--if men of insight, impartiality, and truly popular
gifts, turn their attention to it--to secure to it, in a short time,
the requisite elegance also.

Konigsberg, April 1787.

I. Of the difference between Pure and Empirical Knowledge

That all our knowledge begins with experience there can be no doubt.
For how is it possible that the faculty of cognition should be
awakened into exercise otherwise than by means of objects which affect
our senses, and partly of themselves produce representations, partly
rouse our powers of understanding into activity, to compare to
connect, or to separate these, and so to convert the raw material of
our sensuous impressions into a knowledge of objects, which is
called experience? In respect of time, therefore, no knowledge of ours
is antecedent to experience, but begins with it.

But, though all our knowledge begins with experience, it by no means
follows that all arises out of experience. For, on the contrary, it
is quite possible that our empirical knowledge is a compound of that
which we receive through impressions, and that which the faculty of
cognition supplies from itself (sensuous impressions giving merely
the occasion), an addition which we cannot distinguish from the original
element given by sense, till long practice has made us attentive to,
and skilful in separating it. It is, therefore, a question which
requires close investigation, and not to be answered at first sight,
whether there exists a knowledge altogether independent of experience,
and even of all sensuous impressions? Knowledge of this kind is called
a priori, in contradistinction to empirical knowledge, which has its
sources a posteriori, that is, in experience.

But the expression, "a priori," is not as yet definite enough
adequately to indicate the whole meaning of the question above
started. For, in speaking of knowledge which has its sources in
experience, we are wont to say, that this or that may be known a
priori, because we do not derive this knowledge immediately from
experience, but from a general rule, which, however, we have itself
borrowed from experience. Thus, if a man undermined his house, we say,
"he might know a priori that it would have fallen;" that is, he needed
not to have waited for the experience that it did actually fall. But
still, a priori, he could not know even this much. For, that bodies
are heavy, and, consequently, that they fall when their supports are
taken away, must have been known to him previously, by means of

By the term "knowledge a priori," therefore, we shall in the
sequel understand, not such as is independent of this or that kind
of experience, but such as is absolutely so of all experience. Opposed
to this is empirical knowledge, or that which is possible only a
posteriori, that is, through experience. Knowledge a priori is
either pure or impure. Pure knowledge a priori is that with which no
empirical element is mixed up. For example, the proposition, "Every
change has a cause," is a proposition a priori, but impure, because
change is a conception which can only be derived from experience.

II. The Human Intellect, even in an Unphilosophical State,
is in Possession of Certain Cognitions "a priori".

The question now is as to a criterion, by which we may securely
distinguish a pure from an empirical cognition. Experience no doubt
teaches us that this or that object is constituted in such and such
a manner, but not that it could not possibly exist otherwise. Now,
in the first place, if we have a proposition which contains the idea
of necessity in its very conception, it is a if, moreover, it is not
derived from any other proposition, unless from one equally
involving the idea of necessity, it is absolutely priori. Secondly,
an empirical judgement never exhibits strict and absolute, but only
assumed and comparative universality (by induction); therefore, the
most we can say is--so far as we have hitherto observed, there is no
exception to this or that rule. If, on the other hand, a judgement
carries with it strict and absolute universality, that is, admits of
no possible exception, it is not derived from experience, but is valid
absolutely a priori.

Empirical universality is, therefore, only an arbitrary extension of
validity, from that which may be predicated of a proposition valid
in most cases, to that which is asserted of a proposition which
holds good in all; as, for example, in the affirmation, "All bodies
are heavy." When, on the contrary, strict universality characterizes
a judgement, it necessarily indicates another peculiar source of
knowledge, namely, a faculty of cognition a priori. Necessity and
strict universality, therefore, are infallible tests for
distinguishing pure from empirical knowledge, and are inseparably
connected with each other. But as in the use of these criteria the
empirical limitation is sometimes more easily detected than the
contingency of the judgement, or the unlimited universality which we
attach to a judgement is often a more convincing proof than its
necessity, it may be advisable to use the criteria separately, each
being by itself infallible.

Now, that in the sphere of human cognition we have judgements
which are necessary, and in the strictest sense universal,
consequently pure a priori, it will be an easy matter to show. If we
desire an example from the sciences, we need only take any proposition
in mathematics. If we cast our eyes upon the commonest operations of
the understanding, the proposition, "Every change must have a
cause," will amply serve our purpose. In the latter case, indeed,
the conception of a cause so plainly involves the conception of a
necessity of connection with an effect, and of a strict universality
of the law, that the very notion of a cause would entirely
disappear, were we to derive it, like Hume, from a frequent
association of what happens with that which precedes; and the habit
thence originating of connecting representations--the necessity
inherent in the judgement being therefore merely subjective.
Besides, without seeking for such examples of principles existing a
priori in cognition, we might easily show that such principles are
the indispensable basis of the possibility of experience itself, and
consequently prove their existence a priori. For whence could our
experience itself acquire certainty, if all the rules on which it
depends were themselves empirical, and consequently fortuitous? No
one, therefore, can admit the validity of the use of such rules as
first principles. But, for the present, we may content ourselves
with having established the fact, that we do possess and exercise a
faculty of pure a priori cognition; and, secondly, with having pointed
out the proper tests of such cognition, namely, universality and

Not only in judgements, however, but even in conceptions, is an a
priori origin manifest. For example, if we take away by degrees from
our conceptions of a body all that can be referred to mere sensuous
experience--colour, hardness or softness, weight, even
impenetrability--the body will then vanish; but the space which it
occupied still remains, and this it is utterly impossible to
annihilate in thought. Again, if we take away, in like manner, from
our empirical conception of any object, corporeal or incorporeal,
all properties which mere experience has taught us to connect with
it, still we cannot think away those through which we cogitate it as
substance, or adhering to substance, although our conception of
substance is more determined than that of an object. Compelled,
therefore, by that necessity with which the conception of substance
forces itself upon us, we must confess that it has its seat in our
faculty of cognition a priori.

III. Philosophy stands in need of a Science which shall
Determine the Possibility, Principles, and Extent of
Human Knowledge "a priori"

Of far more importance than all that has been above said, is the
consideration that certain of our cognitions rise completely above
the sphere of all possible experience, and by means of conceptions,
to which there exists in the whole extent of experience no
corresponding object, seem to extend the range of our judgements
beyond its bounds. And just in this transcendental or supersensible
sphere, where experience affords us neither instruction nor
guidance, lie the investigations of reason, which, on account of their
importance, we consider far preferable to, and as having a far more
elevated aim than, all that the understanding can achieve within the
sphere of sensuous phenomena. So high a value do we set upon these
investigations, that even at the risk of error, we persist in
following them out, and permit neither doubt nor disregard nor
indifference to restrain us from the pursuit. These unavoidable
problems of mere pure reason are God, freedom (of will), and
immortality. The science which, with all its preliminaries, has for
its especial object the solution of these problems is named
metaphysics--a science which is at the very outset dogmatical, that
is, it confidently takes upon itself the execution of this task
without any previous investigation of the ability or inability of
reason for such an undertaking.

Now the safe ground of experience being thus abandoned, it seems
nevertheless natural that we should hesitate to erect a building
with the cognitions we possess, without knowing whence they come,
and on the strength of principles, the origin of which is
undiscovered. Instead of thus trying to build without a foundation,
it is rather to be expected that we should long ago have put the
question, how the understanding can arrive at these a priori
cognitions, and what is the extent, validity, and worth which they
may possess? We say, "This is natural enough," meaning by the word
natural, that which is consistent with a just and reasonable way of
thinking; but if we understand by the term, that which usually
happens, nothing indeed could be more natural and more
comprehensible than that this investigation should be left long
unattempted. For one part of our pure knowledge, the science of
mathematics, has been long firmly established, and thus leads us to
form flattering expectations with regard to others, though these may
be of quite a different nature. Besides, when we get beyond the bounds
of experience, we are of course safe from opposition in that
quarter; and the charm of widening the range of our knowledge is so
great that, unless we are brought to a standstill by some evident
contradiction, we hurry on undoubtingly in our course. This,
however, may be avoided, if we are sufficiently cautious in the
construction of our fictions, which are not the less fictions on
that account.

Mathematical science affords us a brilliant example, how far,
independently of all experience, we may carry our a priori
knowledge. It is true that the mathematician occupies himself with
objects and cognitions only in so far as they can be represented by
means of intuition. But this circumstance is easily overlooked,
because the said intuition can itself be given a priori, and therefore
is hardly to be distinguished from a mere pure conception. Deceived
by such a proof of the power of reason, we can perceive no limits to
the extension of our knowledge. The light dove cleaving in free flight
the thin air, whose resistance it feels, might imagine that her
movements would be far more free and rapid in airless space. Just in
the same way did Plato, abandoning the world of sense because of the
narrow limits it sets to the understanding, venture upon the wings
of ideas beyond it, into the void space of pure intellect. He did
not reflect that he made no real progress by all his efforts; for he
met with no resistance which might serve him for a support, as it
were, whereon to rest, and on which he might apply his powers, in
order to let the intellect acquire momentum for its progress. It is,
indeed, the common fate of human reason in speculation, to finish
the imposing edifice of thought as rapidly as possible, and then for
the first time to begin to examine whether the foundation is a solid
one or no. Arrived at this point, all sorts of excuses are sought
after, in order to console us for its want of stability, or rather,
indeed, to enable Us to dispense altogether with so late and dangerous
an investigation. But what frees us during the process of building
from all apprehension or suspicion, and flatters us into the belief
of its solidity, is this. A great part, perhaps the greatest part,
of the business of our reason consists in the analysation of the
conceptions which we already possess of objects. By this means we gain
a multitude of cognitions, which although really nothing more than
elucidations or explanations of that which (though in a confused
manner) was already thought in our conceptions, are, at least in
respect of their form, prized as new introspections; whilst, so far
as regards their matter or content, we have really made no addition
to our conceptions, but only disinvolved them. But as this process
does furnish a real priori knowledge, which has a sure progress and
useful results, reason, deceived by this, slips in, without being
itself aware of it, assertions of a quite different kind; in which,
to given conceptions it adds others, a priori indeed, but entirely
foreign to them, without our knowing how it arrives at these, and,
indeed, without such a question ever suggesting itself. I shall
therefore at once proceed to examine the difference between these
two modes of knowledge.

IV. Of the Difference Between Analytical and Synthetical Judgements.

In all judgements wherein the relation of a subject to the predicate
is cogitated (I mention affirmative judgements only here; the
application to negative will be very easy), this relation is
possible in two different ways. Either the predicate B belongs to
the subject A, as somewhat which is contained (though covertly) in
the conception A; or the predicate B lies completely out of the conception
A, although it stands in connection with it. In the first instance,
I term the judgement analytical, in the second, synthetical.
Analytical judgements (affirmative) are therefore those in which the
connection of the predicate with the subject is cogitated through
identity; those in which this connection is cogitated without
identity, are called synthetical judgements. The former may be
called explicative, the latter augmentative judgements; because the
former add in the predicate nothing to the conception of the
subject, but only analyse it into its constituent conceptions, which
were thought already in the subject, although in a confused manner;
the latter add to our conceptions of the subject a predicate which
was not contained in it, and which no analysis could ever have
discovered therein. For example, when I say, "All bodies are
extended," this is an analytical judgement. For I need not go beyond
the conception of body in order to find extension connected with it,
but merely analyse the conception, that is, become conscious of the
manifold properties which I think in that conception, in order to
discover this predicate in it: it is therefore an analytical
judgement. On the other hand, when I say, "All bodies are heavy,"
the predicate is something totally different from that which I think
in the mere conception of a body. By the addition of such a predicate,
therefore, it becomes a synthetical judgement.

Judgements of experience, as such, are always synthetical. For it
would be absurd to think of grounding an analytical judgement on
experience, because in forming such a judgement I need not go out of
the sphere of my conceptions, and therefore recourse to the
testimony of experience is quite unnecessary. That "bodies are
extended" is not an empirical judgement, but a proposition which
stands firm a priori. For before addressing myself to experience, I
already have in my conception all the requisite conditions for the
judgement, and I have only to extract the predicate from the
conception, according to the principle of contradiction, and thereby
at the same time become conscious of the necessity of the judgement,
a necessity which I could never learn from experience. On the other
hand, though at first I do not at all include the predicate of
weight in my conception of body in general, that conception still
indicates an object of experience, a part of the totality of
experience, to which I can still add other parts; and this I do when
I recognize by observation that bodies are heavy. I can cognize
beforehand by analysis the conception of body through the
characteristics of extension, impenetrability, shape, etc., all
which are cogitated in this conception. But now I extend my knowledge,
and looking back on experience from which I had derived this
conception of body, I find weight at all times connected with the
above characteristics, and therefore I synthetically add to my
conceptions this as a predicate, and say, "All bodies are heavy." Thus
it is experience upon which rests the possibility of the synthesis
of the predicate of weight with the conception of body, because both
conceptions, although the one is not contained in the other, still
belong to one another (only contingently, however), as parts of a
whole, namely, of experience, which is itself a synthesis of

But to synthetical judgements a priori, such aid is entirely
wanting. If I go out of and beyond the conception A, in order to
recognize another B as connected with it, what foundation have I to
rest on, whereby to render the synthesis possible? I have here no
longer the advantage of looking out in the sphere of experience for
what I want. Let us take, for example, the proposition, "Everything
that happens has a cause." In the conception of "something that
happens," I indeed think an existence which a certain time
antecedes, and from this I can derive analytical judgements. But the
conception of a cause lies quite out of the above conception, and
indicates something entirely different from "that which happens,"
and is consequently not contained in that conception. How then am I
able to assert concerning the general conception--"that which
happens"--something entirely different from that conception, and to
recognize the conception of cause although not contained in it, yet
as belonging to it, and even necessarily? what is here the unknown
= X, upon which the understanding rests when it believes it has found,
out of the conception A a foreign predicate B, which it nevertheless
considers to be connected with it? It cannot be experience, because
the principle adduced annexes the two representations, cause and
effect, to the representation existence, not only with universality,
which experience cannot give, but also with the expression of
necessity, therefore completely a priori and from pure conceptions.
Upon such synthetical, that is augmentative propositions, depends
the whole aim of our speculative knowledge a priori; for although
analytical judgements are indeed highly important and necessary,
they are so, only to arrive at that clearness of conceptions which
is requisite for a sure and extended synthesis, and this alone is a
real acquisition.

V. In all Theoretical Sciences of Reason, Synthetical Judgements
"a priori" are contained as Principles.

1. Mathematical judgements are always synthetical. Hitherto this
fact, though incontestably true and very important in its
consequences, seems to have escaped the analysts of the human mind,
nay, to be in complete opposition to all their conjectures. For as
it was found that mathematical conclusions all proceed according to
the principle of contradiction (which the nature of every apodeictic
certainty requires), people became persuaded that the fundamental
principles of the science also were recognized and admitted in the
same way. But the notion is fallacious; for although a synthetical
proposition can certainly be discerned by means of the principle of
contradiction, this is possible only when another synthetical
proposition precedes, from which the latter is deduced, but never
of itself.

Before all, be it observed, that proper mathematical propositions
are always judgements a priori, and not empirical, because they
carry along with them the conception of necessity, which cannot be
given by experience. If this be demurred to, it matters not; I will
then limit my assertion to pure mathematics, the very conception of
which implies that it consists of knowledge altogether non-empirical
and a priori.

We might, indeed at first suppose that the proposition 7 + 5 = 12 is
a merely analytical proposition, following (according to the principle
of contradiction) from the conception of a sum of seven and five.
But if we regard it more narrowly, we find that our conception of
the sum of seven and five contains nothing more than the uniting of
both sums into one, whereby it cannot at all be cogitated what this
single number is which embraces both. The conception of twelve is by
no means obtained by merely cogitating the union of seven and five;
and we may analyse our conception of such a possible sum as long as
we will, still we shall never discover in it the notion of twelve.
We must go beyond these conceptions, and have recourse to an intuition
which corresponds to one of the two--our five fingers, for example,
or like Segner in his Arithmetic five points, and so by degrees, add
the units contained in the five given in the intuition, to the
conception of seven. For I first take the number 7, and, for the
conception of 5 calling in the aid of the fingers of my hand as
objects of intuition, I add the units, which I before took together
to make up the number 5, gradually now by means of the material image
my hand, to the number 7, and by this process, I at length see the
number 12 arise. That 7 should be added to 5, I have certainly
cogitated in my conception of a sum = 7 + 5, but not that this sum
was equal to 12. Arithmetical propositions are therefore always
synthetical, of which we may become more clearly convinced by trying
large numbers. For it will thus become quite evident that, turn and
twist our conceptions as we may, it is impossible, without having
recourse to intuition, to arrive at the sum total or product by
means of the mere analysis of our conceptions. Just as little is any
principle of pure geometry analytical. "A straight line between two
points is the shortest," is a synthetical proposition. For my
conception of straight contains no notion of quantity, but is merely
qualitative. The conception of the shortest is therefore fore wholly
an addition, and by no analysis can it be extracted from our
conception of a straight line. Intuition must therefore here lend
its aid, by means of which, and thus only, our synthesis is possible.

Some few principles preposited by geometricians are, indeed,
really analytical, and depend on the principle of contradiction.
They serve, however, like identical propositions, as links in the
chain of method, not as principles--for example, a = a, the whole is
equal to itself, or (a+b) > a, the whole is greater than its part.
And yet even these principles themselves, though they derive their
validity from pure conceptions, are only admitted in mathematics
because they can be presented in intuition. What causes us here
commonly to believe that the predicate of such apodeictic judgements
is already contained in our conception, and that the judgement is
therefore analytical, is merely the equivocal nature of the
expression. We must join in thought a certain predicate to a given
conception, and this necessity cleaves already to the conception.
But the question is, not what we must join in thought to the given
conception, but what we really think therein, though only obscurely,
and then it becomes manifest that the predicate pertains to these
conceptions, necessarily indeed, yet not as thought in the
conception itself, but by virtue of an intuition, which must be
added to the conception.

2. The science of natural philosophy (physics) contains in itself
synthetical judgements a priori, as principles. I shall adduce two
propositions. For instance, the proposition, "In all changes of the
material world, the quantity of matter remains unchanged"; or, that,
"In all communication of motion, action and reaction must always be
equal." In both of these, not only is the necessity, and therefore
their origin a priori clear, but also that they are synthetical
propositions. For in the conception of matter, I do not cogitate its
permanency, but merely its presence in space, which it fills. I
therefore really go out of and beyond the conception of matter, in
order to think on to it something a priori, which I did not think in
it. The proposition is therefore not analytical, but synthetical,
and nevertheless conceived a priori; and so it is with regard to the
other propositions of the pure part of natural philosophy.

3. As to metaphysics, even if we look upon it merely as an attempted
science, yet, from the nature of human reason, an indispensable one,
we find that it must contain synthetical propositions a priori. It
is not merely the duty of metaphysics to dissect, and thereby
analytically to illustrate the conceptions which we form a priori of
things; but we seek to widen the range of our a priori knowledge.
For this purpose, we must avail ourselves of such principles as add
something to the original conception--something not identical with,
nor contained in it, and by means of synthetical judgements a
priori, leave far behind us the limits of experience; for example,
in the proposition, "the world must have a beginning," and such
like. Thus metaphysics, according to the proper aim of the science,
consists merely of synthetical propositions a priori.

VI. The Universal Problem of Pure Reason.

It is extremely advantageous to be able to bring a number of
investigations under the formula of a single problem. For in this
manner, we not only facilitate our own labour, inasmuch as we define
it clearly to ourselves, but also render it more easy for others to
decide whether we have done justice to our undertaking. The proper
problem of pure reason, then, is contained in the question: "How are
synthetical judgements a priori possible?"

That metaphysical science has hitherto remained in so vacillating
a state of uncertainty and contradiction, is only to be attributed
to the fact that this great problem, and perhaps even the difference
between analytical and synthetical judgements, did not sooner
suggest itself to philosophers. Upon the solution of this problem,
or upon sufficient proof of the impossibility of synthetical knowledge
a priori, depends the existence or downfall of the science of
metaphysics. Among philosophers, David Hume came the nearest of all
to this problem; yet it never acquired in his mind sufficient
precision, nor did he regard the question in its universality. On
the contrary, he stopped short at the synthetical proposition of the
connection of an effect with its cause (principium causalitatis),
insisting that such proposition a priori was impossible. According
to his conclusions, then, all that we term metaphysical science is
a mere delusion, arising from the fancied insight of reason into that
which is in truth borrowed from experience, and to which habit has
given the appearance of necessity. Against this assertion, destructive
to all pure philosophy, he would have been guarded, had he had our
problem before his eyes in its universality. For he would then have
perceived that, according to his own argument, there likewise could
not be any pure mathematical science, which assuredly cannot exist
without synthetical propositions a priori--an absurdity from which
his good understanding must have saved him.

In the solution of the above problem is at the same time
comprehended the possibility of the use of pure reason in the
foundation and construction of all sciences which contain
theoretical knowledge a priori of objects, that is to say, the
answer to the following questions:

How is pure mathematical science possible?

How is pure natural science possible?

Respecting these sciences, as they do certainly exist, it may with
propriety be asked, how they are possible?--for that they must be
possible is shown by the fact of their really existing.* But as to
metaphysics, the miserable progress it has hitherto made, and the fact
that of no one system yet brought forward, far as regards its true
aim, can it be said that this science really exists, leaves any one
at liberty to doubt with reason the very possibility of its existence.

[*Footnote: As to the existence of pure natural science, or physics,
perhaps many may still express doubts. But we have only to look at
the different propositions which are commonly treated of at the
commencement of proper (empirical) physical science--those, for
example, relating to the permanence of the same quantity of matter,
the vis inertiae, the equality of action and reaction, etc.--to be
soon convinced that they form a science of pure physics (physica pura,
or rationalis), which well deserves to be separately exposed as a
special science, in its whole extent, whether that be great or

Yet, in a certain sense, this kind of knowledge must
unquestionably be looked upon as given; in other words, metaphysics
must be considered as really existing, if not as a science,
nevertheless as a natural disposition of the human mind (metaphysica
naturalis). For human reason, without any instigations imputable to
the mere vanity of great knowledge, unceasingly progresses, urged on
by its own feeling of need, towards such questions as cannot be
answered by any empirical application of reason, or principles derived
therefrom; and so there has ever really existed in every man some
system of metaphysics. It will always exist, so soon as reason
awakes to the exercise of its power of speculation. And now the
question arises: "How is metaphysics, as a natural disposition,
possible?" In other words, how, from the nature of universal human
reason, do those questions arise which pure reason proposes to itself,
and which it is impelled by its own feeling of need to answer as
well as it can?

But as in all the attempts hitherto made to answer the questions
which reason is prompted by its very nature to propose to itself,
for example, whether the world had a beginning, or has existed from
eternity, it has always met with unavoidable contradictions, we must
not rest satisfied with the mere natural disposition of the mind to
metaphysics, that is, with the existence of the faculty of pure
reason, whence, indeed, some sort of metaphysical system always
arises; but it must be possible to arrive at certainty in regard to
the question whether we know or do not know the things of which
metaphysics treats. We must be able to arrive at a decision on the
subjects of its questions, or on the ability or inability of reason
to form any judgement respecting them; and therefore either to extend
with confidence the bounds of our pure reason, or to set strictly
defined and safe limits to its action. This last question, which
arises out of the above universal problem, would properly run thus:
"How is metaphysics possible as a science?"

Thus, the critique of reason leads at last, naturally and
necessarily, to science; and, on the other hand, the dogmatical use
of reason without criticism leads to groundless assertions, against
which others equally specious can always be set, thus ending unavoidably
in scepticism.

Besides, this science cannot be of great and formidable prolixity,
because it has not to do with objects of reason, the variety of
which is inexhaustible, but merely with Reason herself and her
problems; problems which arise out of her own bosom, and are not
proposed to her by the nature of outward things, but by her own
nature. And when once Reason has previously become able completely
to understand her own power in regard to objects which she meets
with in experience, it will be easy to determine securely the extent
and limits of her attempted application to objects beyond the confines
of experience.

We may and must, therefore, regard the attempts hitherto made to
establish metaphysical science dogmatically as non-existent. For
what of analysis, that is, mere dissection of conceptions, is
contained in one or other, is not the aim of, but only a preparation
for metaphysics proper, which has for its object the extension, by
means of synthesis, of our a priori knowledge. And for this purpose,
mere analysis is of course useless, because it only shows what is
contained in these conceptions, but not how we arrive, a priori, at
them; and this it is her duty to show, in order to be able
afterwards to determine their valid use in regard to all objects of
experience, to all knowledge in general. But little self-denial,
indeed, is needed to give up these pretensions, seeing the undeniable,
and in the dogmatic mode of procedure, inevitable contradictions of
Reason with herself, have long since ruined the reputation of every
system of metaphysics that has appeared up to this time. It will
require more firmness to remain undeterred by difficulty from
within, and opposition from without, from endeavouring, by a method
quite opposed to all those hitherto followed, to further the growth
and fruitfulness of a science indispensable to human reason--a science
from which every branch it has borne may be cut away, but whose
roots remain indestructible.

VII. Idea and Division of a Particular Science, under the
Name of a Critique of Pure Reason.

From all that has been said, there results the idea of a
particular science, which may be called the Critique of Pure Reason.
For reason is the faculty which furnishes us with the principles of
knowledge a priori. Hence, pure reason is the faculty which contains
the principles of cognizing anything absolutely a priori. An organon
of pure reason would be a compendium of those principles according
to which alone all pure cognitions a priori can be obtained. The
completely extended application of such an organon would afford us
a system of pure reason. As this, however, is demanding a great deal,
and it is yet doubtful whether any extension of our knowledge be
here possible, or, if so, in what cases; we can regard a science of
the mere criticism of pure reason, its sources and limits, as the
propaedeutic to a system of pure reason. Such a science must not be
called a doctrine, but only a critique of pure reason; and its use,
in regard to speculation, would be only negative, not to enlarge the
bounds of, but to purify, our reason, and to shield it against
error--which alone is no little gain. I apply the term
transcendental to all knowledge which is not so much occupied with
objects as with the mode of our cognition of these objects, so far
as this mode of cognition is possible a priori. A system of such
conceptions would be called transcendental philosophy. But this,
again, is still beyond the bounds of our present essay. For as such
a science must contain a complete exposition not only of our
synthetical a priori, but of our analytical a priori knowledge, it
is of too wide a range for our present purpose, because we do not
require to carry our analysis any farther than is necessary to
understand, in their full extent, the principles of synthesis a
priori, with which alone we have to do. This investigation, which we
cannot properly call a doctrine, but only a transcendental critique,
because it aims not at the enlargement, but at the correction and
guidance, of our knowledge, and is to serve as a touchstone of the
worth or worthlessness of all knowledge a priori, is the sole object
of our present essay. Such a critique is consequently, as far as
possible, a preparation for an organon; and if this new organon should
be found to fail, at least for a canon of pure reason, according to
which the complete system of the philosophy of pure reason, whether
it extend or limit the bounds of that reason, might one day be set
forth both analytically and synthetically. For that this is
possible, nay, that such a system is not of so great extent as to
preclude the hope of its ever being completed, is evident. For we have
not here to do with the nature of outward objects, which is
infinite, but solely with the mind, which judges of the nature of
objects, and, again, with the mind only in respect of its cognition
a priori. And the object of our investigations, as it is not to be
sought without, but, altogether within, ourselves, cannot remain
concealed, and in all probability is limited enough to be completely
surveyed and fairly estimated, according to its worth or
worthlessness. Still less let the reader here expect a critique of
books and systems of pure reason; our present object is exclusively
a critique of the faculty of pure reason itself. Only when we make
this critique our foundation, do we possess a pure touchstone for
estimating the philosophical value of ancient and modern writings on
this subject; and without this criterion, the incompetent historian
or judge decides upon and corrects the groundless assertions of others
with his own, which have themselves just as little foundation.

Transcendental philosophy is the idea of a science, for which the
Critique of Pure Reason must sketch the whole plan
architectonically, that is, from principles, with a full guarantee
for the validity and stability of all the parts which enter into the
building. It is the system of all the principles of pure reason. If
this Critique itself does not assume the title of transcendental
philosophy, it is only because, to be a complete system, it ought to
contain a full analysis of all human knowledge a priori. Our
critique must, indeed, lay before us a complete enumeration of all
the radical conceptions which constitute the said pure knowledge. But
from the complete analysis of these conceptions themselves, as also
from a complete investigation of those derived from them, it abstains
with reason; partly because it would be deviating from the end in view
to occupy itself with this analysis, since this process is not
attended with the difficulty and insecurity to be found in the
synthesis, to which our critique is entirely devoted, and partly
because it would be inconsistent with the unity of our plan to
burden this essay with the vindication of the completeness of such
an analysis and deduction, with which, after all, we have at present
nothing to do. This completeness of the analysis of these radical
conceptions, as well as of the deduction from the conceptions a priori
which may be given by the analysis, we can, however, easily attain,
provided only that we are in possession of all these radical
conceptions, which are to serve as principles of the synthesis, and
that in respect of this main purpose nothing is wanting.

To the Critique of Pure Reason, therefore, belongs all that
constitutes transcendental philosophy; and it is the complete idea
of transcendental philosophy, but still not the science itself;
because it only proceeds so far with the analysis as is necessary to
the power of judging completely of our synthetical knowledge a priori.

The principal thing we must attend to, in the division of the
parts of a science like this, is that no conceptions must enter it
which contain aught empirical; in other words, that the knowledge a
priori must be completely pure. Hence, although the highest principles
and fundamental conceptions of morality are certainly cognitions a
priori, yet they do not belong to transcendental philosophy;
because, though they certainly do not lay the conceptions of pain,
pleasure, desires, inclinations, etc. (which are all of empirical
origin), at the foundation of its precepts, yet still into the
conception of duty--as an obstacle to be overcome, or as an incitement
which should not be made into a motive--these empirical conceptions
must necessarily enter, in the construction of a system of pure
morality. Transcendental philosophy is consequently a philosophy of
the pure and merely speculative reason. For all that is practical,
so far as it contains motives, relates to feelings, and these belong
to empirical sources of cognition.

If we wish to divide this science from the universal point of view
of a science in general, it ought to comprehend, first, a Doctrine
of the Elements, and, secondly, a Doctrine of the Method of pure
reason. Each of these main divisions will have its subdivisions, the
separate reasons for which we cannot here particularize. Only so
much seems necessary, by way of introduction of premonition, that
there are two sources of human knowledge (which probably spring from
a common, but to us unknown root), namely, sense and understanding.
By the former, objects are given to us; by the latter, thought. So
far as the faculty of sense may contain representations a priori, which
form the conditions under which objects are given, in so far it
belongs to transcendental philosophy. The transcendental doctrine of
sense must form the first part of our science of elements, because
the conditions under which alone the objects of human knowledge are
given must precede those under which they are thought.



SS I. Introductory.

In whatsoever mode, or by whatsoever means, our knowledge may relate
to objects, it is at least quite clear that the only manner in which
it immediately relates to them is by means of an intuition. To this
as the indispensable groundwork, all thought points. But an intuition
can take place only in so far as the object is given to us. This, again,
is only possible, to man at least, on condition that the object affect
the mind in a certain manner. The capacity for receiving
representations (receptivity) through the mode in which we are
affected by objects, objects, is called sensibility. By means of
sensibility, therefore, objects are given to us, and it alone
furnishes us with intuitions; by the understanding they are thought,
and from it arise conceptions. But an thought must directly, or
indirectly, by means of certain signs, relate ultimately to
intuitions; consequently, with us, to sensibility, because in no other
way can an object be given to us.

The effect of an object upon the faculty of representation, so far
as we are affected by the said object, is sensation. That sort of
intuition which relates to an object by means of sensation is called
an empirical intuition. The undetermined object of an empirical
intuition is called phenomenon. That which in the phenomenon
corresponds to the sensation, I term its matter; but that which
effects that the content of the phenomenon can be arranged under
certain relations, I call its form. But that in which our sensations
are merely arranged, and by which they are susceptible of assuming
a certain form, cannot be itself sensation. It is, then, the matter
of all phenomena that is given to us a posteriori; the form must lie
ready a priori for them in the mind, and consequently can be
regarded separately from all sensation.

I call all representations pure, in the transcendental meaning of
the word, wherein nothing is met with that belongs to sensation. And
accordingly we find existing in the mind a priori, the pure form of
sensuous intuitions in general, in which all the manifold content of
the phenomenal world is arranged and viewed under certain relations.
This pure form of sensibility I shall call pure intuition. Thus, if
I take away from our representation of a body all that the
understanding thinks as belonging to it, as substance, force,
divisibility, etc., and also whatever belongs to sensation, as
impenetrability, hardness, colour, etc.; yet there is still
something left us from this empirical intuition, namely, extension
and shape. These belong to pure intuition, which exists a priori in
the mind, as a mere form of sensibility, and without any real object
of the senses or any sensation.

The science of all the principles of sensibility a priori, I call
transcendental aesthetic.* There must, then, be such a science forming
the first part of the transcendental doctrine of elements, in
contradistinction to that part which contains the principles of pure
thought, and which is called transcendental logic.

[Footnote: The Germans are the only people who at present use this
word to indicate what others call the critique of taste. At the foundation
of this term lies the disappointed hope, which the eminent analyst,
Baumgarten, conceived, of subjecting the criticism of the beautiful
to principles of reason, and so of elevating its rules into a science.
But his endeavours were vain. For the said rules or criteria are, in
respect to their chief sources, merely empirical, consequently never
can serve as determinate laws a priori, by which our judgement in
matters of taste is to be directed. It is rather our judgement which
forms the proper test as to the correctness of the principles. On this
account it is advisable to give up the use of the term as
designating the critique of taste, and to apply it solely to that
doctrine, which is true science--the science of the laws of
sensibility--and thus come nearer to the language and the sense of
the ancients in their well-known division of the objects of cognition
into aiotheta kai noeta, or to share it with speculative philosophy,
and employ it partly in a transcendental, partly in a psychological

In the science of transcendental aesthetic accordingly, we shall
first isolate sensibility or the sensuous faculty, by separating
from it all that is annexed to its perceptions by the conceptions of
understanding, so that nothing be left but empirical intuition. In
the next place we shall take away from this intuition all that belongs
to sensation, so that nothing may remain but pure intuition, and the
mere form of phenomena, which is all that the sensibility can afford
a priori. From this investigation it will be found that there are two
pure forms of sensuous intuition, as principles of knowledge a priori,
namely, space and time. To the consideration of these we shall now

SECTION I. Of Space.

SS 2. Metaphysical Exposition of this Conception.

By means of the external sense (a property of the mind), we
represent to ourselves objects as without us, and these all in
space. Herein alone are their shape, dimensions, and relations to each
other determined or determinable. The internal sense, by means of
which the mind contemplates itself or its internal state, gives,
indeed, no intuition of the soul as an object; yet there is
nevertheless a determinate form, under which alone the contemplation
of our internal state is possible, so that all which relates to the
inward determinations of the mind is represented in relations of time.
Of time we cannot have any external intuition, any more than we can
have an internal intuition of space. What then are time and space?
Are they real existences? Or, are they merely relations or
determinations of things, such, however, as would equally belong to
these things in themselves, though they should never become objects
of intuition; or, are they such as belong only to the form of
intuition, and consequently to the subjective constitution of the
mind, without which these predicates of time and space could not be
attached to any object? In order to become informed on these points,
we shall first give an exposition of the conception of space. By
exposition, I mean the clear, though not detailed, representation of
that which belongs to a conception; and an exposition is
metaphysical when it contains that which represents the conception
as given a priori.

1. Space is not a conception which has been derived from outward
experiences. For, in order that certain sensations may relate to
something without me (that is, to something which occupies a different
part of space from that in which I am); in like manner, in order
that I may represent them not merely as without, of, and near to
each other, but also in separate places, the representation of space
must already exist as a foundation. Consequently, the representation
of space cannot be borrowed from the relations of external phenomena
through experience; but, on the contrary, this external experience
is itself only possible through the said antecedent representation.

2. Space then is a necessary representation a priori, which serves
for the foundation of all external intuitions. We never can imagine
or make a representation to ourselves of the non-existence of space,
though we may easily enough think that no objects are found in it.
It must, therefore, be considered as the condition of the
possibility of phenomena, and by no means as a determination dependent
on them, and is a representation a priori, which necessarily
supplies the basis for external phenomena.

3. Space is no discursive, or as we say, general conception of the
relations of things, but a pure intuition. For, in the first place,
we can only represent to ourselves one space, and, when we talk of
divers spaces, we mean only parts of one and the same space. Moreover,
these parts cannot antecede this one all-embracing space, as the
component parts from which the aggregate can be made up, but can be
cogitated only as existing in it. Space is essentially one, and
multiplicity in it, consequently the general notion of spaces, of this
or that space, depends solely upon limitations. Hence it follows
that an a priori intuition (which is not empirical) lies at the root
of all our conceptions of space. Thus, moreover, the principles of
geometry--for example, that "in a triangle, two sides together are
greater than the third," are never deduced from general conceptions
of line and triangle, but from intuition, and this a priori, with
apodeictic certainty.

4. Space is represented as an infinite given quantity. Now every
conception must indeed be considered as a representation which is
contained in an infinite multitude of different possible
representations, which, therefore, comprises these under itself; but
no conception, as such, can be so conceived, as if it contained within
itself an infinite multitude of representations. Nevertheless, space
is so conceived of, for all parts of space are equally capable of
being produced to infinity. Consequently, the original
representation of space is an intuition a priori, and not a

SS 3. Transcendental Exposition of the Conception of Space.

By a transcendental exposition, I mean the explanation of a
conception, as a principle, whence can be discerned the possibility
of other synthetical a priori cognitions. For this purpose, it is
requisite, firstly, that such cognitions do really flow from the given
conception; and, secondly, that the said cognitions are only
possible under the presupposition of a given mode of explaining this

Geometry is a science which determines the properties of space
synthetically, and yet a priori. What, then, must be our
representation of space, in order that such a cognition of it may be
possible? It must be originally intuition, for from a mere conception,
no propositions can be deduced which go out beyond the conception,
and yet this happens in geometry. (Introd. V.) But this intuition must
be found in the mind a priori, that is, before any perception of
objects, consequently must be pure, not empirical, intuition. For
geometrical principles are always apodeictic, that is, united with
the consciousness of their necessity, as: "Space has only three
dimensions." But propositions of this kind cannot be empirical
judgements, nor conclusions from them. (Introd. II.) Now, how can an
external intuition anterior to objects themselves, and in which our
conception of objects can be determined a priori, exist in the human
mind? Obviously not otherwise than in so far as it has its seat in
the subject only, as the formal capacity of the subject's being affected
by objects, and thereby of obtaining immediate representation, that
is, intuition; consequently, only as the form of the external sense
in general.

Thus it is only by means of our explanation that the possibility
of geometry, as a synthetical science a priori, becomes
comprehensible. Every mode of explanation which does not show us
this possibility, although in appearance it may be similar to ours,
can with the utmost certainty be distinguished from it by these marks.

SS 4. Conclusions from the foregoing Conceptions.

(a) Space does not represent any property of objects as
things in themselves, nor does it represent them in their relations
to each other; in other words, space does not represent to us any
determination of objects such as attaches to the objects themselves,
and would remain, even though all subjective conditions of the
intuition were abstracted. For neither absolute nor relative
determinations of objects can be intuited prior to the existence of
the things to which they belong, and therefore not a priori.

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