Critique of Pure Reason (Introduction)

Immanuel Kant's
Critique
trans. by Norman Kemp Smith
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INTRODUCTION
1. THE DISTINCTION BETWEEN PURE AND EMPIRICAL
KNOWLEDGE
THERE can be no doubt that all our knowledge begins with
experience. For how should our faculty of knowledge be
awakened into action did not objects affecting our senses
partly of themselves produce representations, partly arouse
the activity of our understanding to compare these 
representations, and, by combining or separating them, work
up the raw material of the sensible impressions into that
knowledge of objects which is entitled experience? In the
order of time, therefore, we have no knowledge antecedent to
experience, and with experience all our knowledge begins.
But though all our knowledge begins with experience,
it does not follow that it all arises out of experience.
I. THE IDEA OF TRANSCENDENTAL PHILOSOPHY
Experience is, beyond all doubt, the first product to which
our understanding gives rise, in working up the raw material
of sensible impressions. Experience is therefore our first
instruction, and in its progress is so inexhaustible in new
information, that in the interconnected lives of all future
generations there will never be any lack of new knowledge
that can be thus ingathered. Nevertheless, it is by no means
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the sole field to which our understanding is confined.
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For it
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may well be that even our empirical knowledge is made up of
what we receive through impressions and of what our own
faculty of knowledge (sensible impressions serving merely as
the occasion) supplies from itself. If our faculty of knowledge
makes any such addition, it may be that we are not in a position
to distinguish it from the raw material, until with long
practice of attention we have become skilled in separating it.
This, then, is a question which at least calls for closer
examination, and does not allow of any off-hand answer: --
whether there is any knowledge that is thus independent of
experience and even of all impressions of the senses. Such
knowledge is entitled a priori, and distinguished from the
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empirical, which has its sources a posteriori, that is, in 
experience. 
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Experi-
ence tells us, indeed, what is, but not that it must necessarily
be so, and not otherwise. It therefore gives us no true
universality; and reason, which is so insistent upon this
kind of knowledge, is therefore more stimulated by it than
satisfied. Such universal modes of knowledge, which at the
same time possess the character of inner necessity, must in
themselves, independently of experience, be clear and certain.
They are therefore entitled knowledge a priori; whereas, on
the other hand, that which is borrowed solely from experience
is, as we say, known only a posteriori, or empirically.
Now we find, what is especially noteworthy, that even into
our experiences there enter modes of knowledge which must
have their origin a priori, and which perhaps serve only to
give coherence to our sense-representations. For if we 
eliminate from our experiences everything which belongs to the
senses, there still remain certain original concepts and certain
judgments derived from them, which must have arisen 
completely a priori, independently of experience, inasmuch as
they enable us to say, or at least lead us to believe that we can
say, in regard to the objects which appear to the senses, more
than mere experience would teach -- giving to assertions true
universality and strict necessity, such as mere empirical 
knowledge cannot supply.
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The expression 'a priori' does not, however, indicate with
sufficient precision the full meaning of our question. For it
has been customary to say, even of much knowledge that is
derived from empirical sources, that we have it or are capable
of having it a priori, meaning thereby that we do not derive
it immediately from experience, but from a universal rule -- a
rule which is itself, however, borrowed by us from experience.
Thus we would say of a man who undermined the foundations
of his house, that he might have known a priori that it would
fall, that is, that he need not have waited for the experience of
its actual falling. But still he could not know this completely
a priori. For he had first to learn through experience that
bodies are heavy, and therefore fall when their supports are
withdrawn.
In what follows, therefore, we shall understand by a priori
knowledge, not knowledge independent of this or that experience,
but knowledge absolutely independent of all experience.
Opposed to it is empirical knowledge, which is knowledge
possible only a posteriori, that is, through experience. A -
priori modes of knowledge are entitled pure when there is
no admixture of anything empirical. Thus, for instance, the
proposition, 'every alteration has its cause', while an a priori
proposition, is not a pure proposition, because alteration is a
concept which can be derived only from experience.
II. WE ARE IN POSSESSION OF CERTAIN MODES OF A PRIORI
KNOWLEDGE, AND EVEN THE COMMON 
UNDERSTANDING IS NEVER WITHOUT THEM
What we here require is a criterion by which to distinguish
with certainty between pure and empirical knowledge. Experience
teaches us that a thing is so and so, but not that it
cannot be otherwise. First, then, if we have a proposition
which in being thought is thought as necessary, it is an a priori
judgment; and if, besides, it is not derived from any proposition
except one which also has the validity of a necessary
judgment, it is an absolutely a priori judgment. Secondly,
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experience never confers on its judgments true or strict but
only assumed and comparative universality, through induction.
We can properly only say, therefore, that so far as
we have hitherto observed, there is no exception to this or
that rule. If, then, a judgment is thought with strict universality,
that is, in such manner that no exception is allowed as
possible, it is not derived from experience, but is valid absolutely
a priori. Empirical universality is only an arbitrary extension
of a validity holding in most cases to one which holds
in all, for instance, in the proposition, 'all bodies are heavy'.
When, on the other hand, strict universality is essential to a
a judgment, this indicates a special source of knowledge,
namely, a faculty of a priori knowledge. Necessity and strict
universality are thus sure criteria of a priori knowledge, and
are inseparable from one another. But since in the employment
of these criteria the contingency of judgments is sometimes
more easily shown than their empirical limitation, or,
as sometimes also happens, their unlimited universality can
be more convincingly proved than their necessity, it is advisable
to use the two criteria separately, each by itself being
infallible.
Now it is easy to show that there actually are in human
knowledge judgments which are necessary and in the strictest
sense universal, and which are therefore pure a priori 
judgments. If an example from the sciences be desired, we have
only to look to any of the propositions of mathematics; if we
seek an example from the understanding in its quite ordinary
employment, the proposition, 'every alteration must have a
cause', will serve our purpose. In the latter case, indeed, the
very concept of a cause so manifestly contains the concept of
a necessity of connection with an effect and of the strict 
universality of the rule, that the concept would be altogether lost if
we attempted to derive it, as Hume has done, from a repeated
association of that which happens with that which precedes,
and from a custom of connecting representations, a custom
originating in this repeated association, and constituting
therefore a merely subjective necessity. Even without appealing
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to such examples, it is possible to show that pure a priori
principles are indispensable for the possibility of experience,
and so to prove their existence a priori. For whence could
experience derive its certainty, if all the rules, according to
which it proceeds, were always themselves empirical, and
therefore contingent? Such rules could hardly be regarded as
first principles. At present, however, we may be content to
have established the fact that our faculty of knowledge does
have a pure employment, and to have shown what are the
criteria of such an employment.
Such a priori origin is manifest in certain concepts, no
less than in judgments. If we remove from our empirical
concept of a body, one by one, every feature in it which is
[merely] empirical, the colour, the hardness or softness, the
weight, even the impenetrability, there still remains the
space which the body (now entirely vanished) occupied, and
this cannot be removed. Again, if we remove from our empirical
concept of any object, corporeal or incorporeal, all
properties which experience has taught us, we yet cannot take
away that property through which the object is thought as
substance or as inhering in a substance (although this concept
of substance is more determinate than that of an object in
general). Owing, therefore, to the necessity with which this
concept of substance forces itself upon us, we have no option
save to admit that it has its seat in our faculty of a priori
knowledge.
III. PHILOSOPHY STANDS IN NEED OF A SCIENCE WHICH
SHALL DETERMINE THE POSSIBILITY, THE PRINCIPLES,
AND THE EXTENT OF ALL A PRIORI KNOWLEDGE
But what is still more extraordinary than all the preceding
is this, that certain modes of knowledge leave the field of all
possible experiences and have the appearance of extending
the scope of our judgments beyond all limits of experience,
and this by means of concepts to which no corresponding
object can ever be given in experience.
It is precisely by means of the latter modes of knowledge,
in a realm beyond the world of the senses, where experience
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can yield neither guidance nor correction, that our reason
carries on those enquiries which owing to their importance
we consider to be far more excellent, and in their purpose
far more lofty, than all that the understanding can learn in
the field of appearances. Indeed we prefer to run every risk
of error rather than desist from such urgent enquiries, on the
ground of their dubious character, or from disdain and 
indifference. These unavoidable problems set by pure reason
itself are God, freedom, and immortality. The science which,
with all its preparations, is in its final intention directed
solely to their solution is metaphysics; and its procedure
is at first dogmatic, that is, it confidently sets itself to this
task without any previous examination of the capacity or
incapacity of reason for so great an undertaking.
Now it does indeed seem natural that, as soon as we have
left the ground of experience, we should, through careful 
enquiries, assure ourselves as to the foundations of any building
that we propose to erect, not making use of any knowledge
that we possess without first determining whence it has come,
and not trusting to principles without knowing their origin.
It is natural, that is to say, that the question should first be
considered, how the understanding can arrive at all this 
knowledge a priori, and what extent, validity, and worth it may
have. Nothing, indeed, could be more natural, if by the term
'natural' we signify what fittingly and reasonably ought to
happen. But if we mean by 'natural' what ordinarily happens,
then on the contrary nothing is more natural and more intelligible
than the fact that this enquiry has been so long neglected.
For one part of this knowledge, the mathematical, has
long been of established reliability, and so gives rise to a 
favourable presumption as regards the other part, which may yet be of
quite different nature. Besides, once we are outside the circle
of experience, we can be sure of not being contradicted by
experience. The charm of extending our knowledge is so
great that nothing short of encountering a direct contradiction
can suffice to arrest us in our course; and this can be
avoided, if we are careful in our fabrications -- which none the
less will still remain fabrications. Mathematics gives us a 
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shining example of how far, independently of experience, we can
progress in a priori knowledge. It does, indeed, occupy itself
with objects and with knowledge solely in so far as they allow
of being exhibited in intuition. But this circumstance is easily
overlooked, since the intuition, in being thought, can itself be
given a priori, and is therefore hardly to be distinguished from
a bare and pure concept. Misled by such a proof of the power
of reason, the demand for the extension of knowledge recognises
no limits. The light dove, cleaving the air in her free
flight, and feeling its resistance, might imagine that its flight
would be still easier in empty space. It was thus that Plato
left the world of the senses, as setting too narrow limits to
the understanding, and ventured out beyond it on the wings
of the ideas, in the empty space of the pure understanding.
He did not observe that with all his efforts he made no 
advance -- meeting no resistance that might, as it were, serve
as a support upon which he could take a stand, to which
he could apply his powers, and so set his understanding
in motion. It is, indeed, the common fate of human reason
to complete its speculative structures as speedily as may
be, and only afterwards to enquire whether the foundations
are reliable. All sorts of excuses will then be appealed to, in
order to reassure us of their solidity, or rather indeed to
enable us to dispense altogether with so late and so dangerous
an enquiry. But what keeps us, during the actual building,
free from all apprehension and suspicion, and flatters us with
a seeming thoroughness, is this other circumstance, namely,
that a great, perhaps the greatest, part of the business of our
reason consists in analysis of the concepts which we already
have of objects. This analysis supplies us with a considerable
body of knowledge, which, while nothing but explanation
or elucidation of what has already been thought in our 
concepts, though in a confused manner, is yet prized as being,
at least as regards its form, new insight. But so far as the
matter or content is concerned, there has been no extension of
our previously possessed concepts, but only an analysis of them.
Since this procedure yields real knowledge a priori, which
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progresses in an assured and useful fashion, reason is so far
misled as surreptitiously to introduce, without itself being
aware of so doing, assertions of an entirely different order, in
which it attaches to given concepts others completely foreign
to them, and moreover attaches them a priori. And yet it is
not known how reason can be in position to do this. Such a
question is never so much as thought of. I shall therefore
at once proceed to deal with the difference between these two
kinds of knowledge.
 IV. THE DISTINCTION BETWEEN ANALYTIC AND
SYNTHETIC JUDGMENTS
In all judgments in which the relation of a subject to the
predicate is thought (I take into consideration affirmative
judgments only, the subsequent application to negative 
judgments being easily made), this relation is possible in two
different ways. Either the predicate to the subject
A, as something which is (covertly) contained in this concept
A; or outside the concept A, although it does indeed
stand in connection with it. In the one case I entitle the 
judgment analytic, in the other synthetic. Analytic judgments
(affirmative) are therefore those in which the connection of the
predicate with the subject is thought through identity; those
in which this connection is thought without identity should
 be entitled synthetic. The former, as adding nothing through
the predicate to the concept of the subject, but merely breaking
it up into those constituent concepts that have all along
been thought in it, although confusedly, can also be entitled
explicative. The latter, on the other hand, add to the concept
of the subject a predicate which has not been in any wise thought
in it, and which no analysis could possibly extract from it; and
they may therefore be entitled ampliative. If I say, for instance,
'All bodies are extended', this is an analytic judgment. For I
do not require to go beyond the concept which I connect with
'body' in order to find extension as bound up with it. To
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meet with this predicate, I have merely to analyse the concept,
that is, to become conscious to myself of the manifold which
I always think in that concept. The judgment is therefore
analytic. But when I say, 'All bodies are heavy', the predicate
is something quite different from anything that I think in
the mere concept of body in general; and the addition of such
a predicate therefore yields a synthetic judgment.
* Judgments of experience, as such, are one and all synthetic.
For it would be absurd to found an analytic judgment on 
experience. Since, in framing the judgment, I must not go 
outside my concept, there is no need to appeal to the testimony
of experience in its support. That a body is extended is a 
proposition that holds a priori and is not empirical. For, before
appealing to experience, I have already in the concept of body
all the conditions required for my judgment. I have only to extract
from it, in accordance with the principle of contradiction,
the required predicate, and in so doing can at the same time
become conscious of the necessity of the judgment -- and that
is what experience could never have taught me. On the other
hand, though I do not include in the concept of a body in
general the predicate 'weight', none the less this concept 
indicates an object of experience through one of its parts, and I
can add to that part other parts of this same experience, as in
this way belonging together with the concept.
*Thus it is evident: 1. that through analytic judgments our
knowledge is not in any way extended, and that the concept
which I already have is merely set forth and made intelligible
to me; 2. that in synthetic judgments I must have besides the
concept of the subject something else (X), upon which the 
understanding may rely, if it is to know that a predicate, not
contained in this concept, nevertheless belongs to it.
In the case of empirical judgments, judgments of experience,
there is no difficulty whatsoever in meeting this demand.
This X is the complete experience of the object which I think
through the concept A -- a concept which forms only one part
of this experience.
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From the start
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I can apprehend the concept of body analytically through the
characters of extension, impenetrability, figure, etc. , all of
which are thought in the concept. Now, however, looking
back on the experience from which I have derived this concept
of body, and finding weight to be invariably connected
with the above characters, I attach it as a predicate to the
concept; and in doing so I attach it synthetically, and am
therefore extending my knowledge. The possibility of the synthesis
of the predicate 'weight' with the concept of 'body' thus
rests upon experience. While the one concept is not contained
in the other, they yet belong to one another, though only 
contingently, as parts of a whole, namely, of an experience which
is itself a synthetic combination of intuitions.
 But in a priori synthetic judgments this help is entirely
lacking. [I do not here have the advantage of looking around
in the field of experience. ] Upon what, then, am I to rely, when
I seek to go beyond the concept A, and to know that another
concept B is connected with it? Through what is the synthesis
made possible? Let us take the proposition, 'Everything
which happens has its cause'. In the concept of 'something
which happens', I do indeed think an existence which is
preceded by a time, etc. , and from this concept analytic 
judgments may be obtained.
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For though I do not include in the concept
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of a body in general the predicate 'weight', the concept none
the less indicates the complete experience through one of its
parts; and to this part, as belonging to it, I can therefore add
other parts of the same experience. By prior analysis I can 
apprehend the concept of body through the characters of extension,
impenetrability, figure, etc. , all of which are thought in
this concept. To extend my knowledge, I then look back to the
experience from which I have derived this concept of body, and
find that weight is always connected with the above characters.
Experience is thus the X which lies outside the concept A,
and on which rests the possibility of the synthesis of the
predicate 'weight' (B) with the concept (A).
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But the concept of a 'cause' lies entirely
outside the other concept, and signifies something different
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from 'that which happens', and is not therefore in any way
contained in this latter representation. How come I then to
predicate of that which happens something quite different,
and to apprehend that the concept of cause, though not contained
in it, yet belongs, and indeed necessarily belongs to it?
What is here the unknown = X which gives support to the
understanding when it believes that it can discover outside
the concept A a predicate B foreign to this concept, which
it yet at the same time considers to be connected with it?
It cannot be experience, because the suggested principle has
connected the second representation with the first, not only
with greater universality, but also with the character of
necessity, and therefore completely a priori and on the basis
of mere concepts. Upon such synthetic, that is, ampliative
principles, all our a priori speculative knowledge must ultimately
rest; analytic judgments are very important, and indeed
necessary, but only for obtaining that clearness in the concepts
which is requisite for such a sure and wide synthesis as
will lead to a genuinely new addition to all previous 
knowledge. 
* A certain mystery lies here concealed; and only upon
its solution can the advance into the limitless field of the
knowledge yielded by pure understanding be made sure and
trustworthy. What we must do is to discover, in all its proper
universality, the ground of the possibility of a priori synthetic
judgments, to obtain insight into the conditions which make
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each kind of such judgments possible, and to mark out all this
knowledge, which forms a genus by itself, not in any cursory
outline, but in a system, with completeness and in a manner
sufficient for any use, according to its original sources, 
divisions, extent, and limits. So much, meantime, as regards
what is peculiar in synthetic judgments.
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* If it had occurred to any of the ancients even to raise this
question, this by itself would, up to our own time, have been a 
powerful influence against all systems of pure reason, and would have
saved us so many of those vain attempts, which have been blindly
undertaken without knowledge of what it is that requires to be done.
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V. IN ALL THEORETICAL SCIENCES OF REASON SYNTHETIC
A PRIORI JUDGMENTS ARE CONTAINED AS PRINCIPLES
1. All mathematical judgments, without exception, are
synthetic. This fact, though incontestably certain and in
its consequences very important, has hitherto escaped the
notice of those who are engaged in the analysis of human
reason, and is, indeed, directly opposed to all their conjectures.
For as it was found that all mathematical inferences proceed
in accordance with the principle of contradiction (which the
nature of all apodeictic certainty requires), it was supposed that
the fundamental propositions of the science can themselves be
known to be true through that principle. This is an erroneous
view. For though a synthetic proposition can indeed be discerned
in accordance with the principle of contradiction, this
can only be if another synthetic proposition is presupposed,
and if it can then be apprehended as following from this other
proposition; it can never be so discerned in and by itself.
First of all, it has to be noted that mathematical propositions,
strictly so called, are always judgments a priori, not
empirical; because they carry with them necessity, which
 cannot be derived from experience. If this be demurred to,
I am willing to limit my statement to pure mathematics, the
very concept of which implies that it does not contain empirical,
but only pure a priori knowledge.
We might, indeed, at first suppose that the proposition
7 & 5 = 12 is a merely analytic proposition, and follows by
the principle of contradiction from the concept of a sum of
7 and 5. But if we look more closely we find that the concept
of the sum of 7 and 5 contains nothing save the union of the
two numbers into one, and in this no thought is being taken
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as to what that single number may be which combines both.
The concept of 12 is by no means already thought in merely
thinking this union of 7 and 5; and I may analyse my concept
of such a possible sum as long as I please, still I shall never
find the 12 in it. We have to go outside these concepts, and
call in the aid of the intuition which corresponds to one of
them, our five fingers, for instance, or, as Segner does in his
Arithmetic, five points, adding to the concept of 7, unit by
unit, the five given in intuition. For starting with the number
7, and for the concept of 5 calling in the aid of the fingers of
my hand as intuition, I now add one by one to the number 7
the units which I previously took together to form the number
5, and with the aid of that figure [the hand] see the number 12
come into being. That 5 should be added to 7, I have indeed
already thought in the concept of a sum = 7 & 5, but not that
this sum is equivalent to the number 12. Arithmetical 
propositions are therefore always synthetic. This is still more
evident if we take larger numbers. For it is then obvious that,
however we might turn and twist our concepts, we could
never, by the mere analysis of them, and without the aid of
intuition, discover what [the number is that] is the sum.
Just as little is any fundamental proposition of pure
geometry analytic. That the straight line between two points
is the shortest, is a synthetic proposition. For my concept of
straight contains nothing of quantity, but only of quality. The
concept of the shortest is wholly an addition, and cannot be
derived, through any process of analysis, from the concept of
the straight line. Intuition, therefore, must here be called in;
only by its aid is the synthesis possible. What here causes
us commonly to believe that the predicate of such apodeictic
judgments is already contained in our concept, and that the
judgment is therefore analytic, is merely the ambiguous
character of the terms used. We are required to join in
thought a certain predicate to a given concept, and this necessity
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is inherent in the concepts themselves. But the question is
not what we ought to join in thought to the given concept, but
what we actually think in it, even if only obscurely; and it is
then manifest that, while the predicate is indeed attached
necessarily to the concept, it is so in virtue of an intuition
which must be added to the concept, not as thought in the
concept itself.
 Some few fundamental propositions, presupposed by the
geometrician, are, indeed, really analytic, and rest on the
principle of contradiction. But, as identical propositions, they
serve only as links in the chain of method and not as principles;
for instance, a = a; the whole is equal to itself; or
(a & b)  a, that is, the whole is greater than its part. And even
these propositions, though they are valid according to pure
concepts, are only admitted in mathematics because they can
be exhibited in intuition.
2. Natural science (physics) contains a priori synthetic
judgments as principles. I need cite only two such judgments:
that in all changes of the material world the quantity of matter
remains unchanged; and that in all communication of motion,
action and reaction must always be equal. Both propositions,
it is evident, are not only necessary, and therefore in their origin
a priori, but also synthetic. For in the concept of matter I do
not think its permanence, but only its presence in the space
which it occupies. I go outside and beyond the concept of
matter, joining to it a priori in thought something which I
have not thought in it. The proposition is not, therefore, analytic,
but synthetic, and yet is thought a priori; and so likewise
are the other propositions of the pure part of natural science.
3. Metaphysics, even if we look upon it as having hitherto
failed in all its endeavours, is yet, owing to the nature of
human reason, a quite indispensable science, and ought to
contain a priori synthetic knowledge. For its business is not
merely to analyse concepts which we make for ourselves a -
priori of things, and thereby to clarify them analytically, but
to extend our a priori knowledge. And for this purpose we
must employ principles which add to the given concept something
that was not contained in it, and through a priori synthetic
judgments venture out so far that experience is quite
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unable to follow us, as, for instance, in the proposition, that
the world must have a first beginning, and such like. Thus
metaphysics consists, at least in intention, entirely of a priori
synthetic propositions.
VI. THE GENERAL PROBLEM OF PURE REASON
Much is already gained if we can bring a number of 
investigations under the formula of a single problem. For we
not only lighten our own task, by defining it accurately, but
make it easier for others, who would test our results, to judge
whether or not we have succeeded in what we set out to do.
Now the proper problem of pure reason is contained in the
question: How are a priori synthetic judgments possible?
That metaphysics has hitherto remained in so vacillating
a state of uncertainty and contradiction, is entirely due to the
fact that this problem, and perhaps even the distinction 
between analytic and synthetic judgments, has never previously
been considered. Upon the solution of this problem, or upon
a sufficient proof that the possibility which it desires to have
explained does in fact not exist at all, depends the success or
failure of metaphysics. Among philosophers, David Hume
came nearest to envisaging this problem, but still was very far
from conceiving it with sufficient definiteness and universality.
He occupied himself exclusively with the synthetic proposition
regarding the connection of an effect with its cause
(principium causalitatis), and he believed himself to have
shown that such an a priori proposition is entirely impossible.
If we accept his conclusions, then all that we call
metaphysics is a mere delusion whereby we fancy ourselves to
have rational insight into what, in actual fact, is borrowed
solely from experience, and under the influence of custom has
taken the illusory semblance of necessity. If he had envisaged
our problem in all its universality, he would never have been
guilty of this statement, so destructive of all pure philosophy.
For he would then have recognised that, according to his own
argument, pure mathematics, as certainly containing a priori
synthetic propositions, would also not be possible; and from
such an assertion his good sense would have saved him.
In the solution of the above problem, we are at the same
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time deciding as to the possibility of the employment of pure
reason in establishing and developing all those sciences which
contain a theoretical a priori knowledge of objects, and have
therefore to answer the questions:
How is pure mathematics possible?
How is pure science of nature possible?
Since these sciences actually exist, it is quite proper to ask
how they are possible; for that they must be possible is proved
by the fact that they exist. But the poor progress which has
hitherto been made in metaphysics, and the fact that no
system yet propounded can, in view of the essential purpose
of metaphysics, be said really to exist, leaves everyone 
sufficient ground for doubting as to its possibility.
Yet, in a certain sense, this kind of knowledge is to be
looked upon as given; that is to say, metaphysics actually
exists, if not as a science, yet still as natural disposition 
(metaphysica naturalis). For human reason, without being moved
merely by the idle desire for extent and variety of knowledge,
proceeds impetuously, driven on by an inward need, to 
questions such as cannot be answered by any empirical employment
of reason, or by principles thence derived. Thus in all
men, as soon as their reason has become ripe for speculation,
there has always existed and will always continue to exist
some kind of metaphysics. And so we have the question:
How is metaphysics, as natural disposition, possible? 
that is, how from the nature of universal human reason do
those questions arise which pure reason propounds to itself,
and which it is impelled by its own need to answer as best it
can?
* Many may still have doubts as regards pure natural science.
We have only, however, to consider the various propositions that are
to be found at the beginning of (empirical) physics, properly so
called, those, for instance, relating to the permanence in the quantity
of matter, to inertia, to the equality of action and reaction, etc. , in
order to be soon convinced that they constitute a physica pura, or
rationalis, which well deserves, as an independent science, to be
separately dealt with in its whole extent, be that narrow or wide.
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But since all attempts which have hitherto been made
to answer these natural questions -- for instance, whether the
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world has a beginning or is from eternity -- have always met
with unavoidable contradictions, we cannot rest satisfied with
the mere natural disposition to metaphysics, that is, with the
pure faculty of reason itself, from which, indeed, some sort of
metaphysics (be it what it may) always arises. It must be
possible for reason to attain to certainty whether we know or
do not know the objects of metaphysics, that is, to come to
a decision either in regard to the objects of its enquiries or in
regard to the capacity or incapacity of reason to pass any
judgment upon them, so that we may either with confidence
extend our pure reason or set to it sure and determinate
limits. This last question, which arises out of the previous
general problem, may, rightly stated, take the form:
How is metaphysics, as science, possible? 
Thus the critique of reason, in the end, necessarily leads to
scientific knowledge; while its dogmatic employment, on the
other hand, lands us in dogmatic assertions to which other
assertions, equally specious, can always be opposed -- that is,
in scepticism.
This science cannot be of any very formidable prolixity,
since it has to deal not with the objects of reason, the variety
of which is inexhaustible, but only with itself and the 
problems which arise entirely from within itself, and which are
imposed upon it by its own nature, not by the nature of things
which are distinct from it. When once reason has learnt completely
to understand its own power in respect of objects which
can be presented to it in experience, it should easily be able to
determine, with completeness and certainty, the extent and
the limits of its attempted employment beyond the bounds of
all experience.
We may, then, and indeed we must, regard as abortive all
attempts, hitherto made, to establish a metaphysic dogmatically.
For the analytic part in any such attempted system,
namely, the mere analysis of the concepts that inhere in our
reason a priori, is by no means the aim of, but only a preparation
for, metaphysics proper, that is, the extension of its a -
priori synthetic knowledge. For such a purpose, the analysis
of concepts is useless, since it merely shows what is contained
in these concepts, not how we arrive at them a priori. A solution
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of this latter problem is required, that we may be able to 
determine the valid employment of such concepts in regard to
the objects of all knowledge in general. Nor is much self-denial
needed to give up these claims, seeing that the undeniable,
and in the dogmatic procedure of reason also unavoidable,
contradictions of reason with itself have long since undermined
the authority of every metaphysical system yet propounded.
Greater firmness will be required if we are not to be deterred
by inward difficulties and outward opposition from endeavouring,
through application of a method entirely different from
any hitherto employed, at last to bring to a prosperous and
fruitful growth a science indispensable to human reason -- a
science whose every branch may be cut away but whose root
cannot be destroyed.
VII. THE IDEA AND DIVISION OF A SPECIAL SCIENCE,
UNDER THE TITLE "CRITIQUE OF PURE REASON"
In view of all these considerations, we arrive at the idea of
a special science which can be entitled the Critique of Pure
Reason. * For reason is the faculty which supplies the principles
of a priori knowledge. Pure reason is, therefore, that which
contains the principles whereby we know anything absolutely
a priori. An organon of pure reason would be the sum-total of
those principles according to which all modes of pure a priori
knowledge can be acquired and actually brought into being.
The exhaustive application of such an organon would give
rise to a system of pure reason. But as this would be asking
rather much, and as it is still doubtful whether, and in what
cases, any extension of our knowledge be here possible, we
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can regard a science of the mere examination of pure reason,
of its sources and limits, as the propaedeutic to the system of
pure reason.
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*Any knowledge is entitled pure, if it be not mixed with 
anything extraneous. But knowledge is more particularly to be
called absolutely pure, if no experience or sensation whatsoever
be mingled with it, and if it be therefore possible 
completely a priori.
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As such, it should be called a critique, not a
doctrine, of pure reason. Its utility, in speculation, ought
properly to be only negative, not to extend, but only to clarify
our reason, and keep it free from errors -- which is already
a very great gain. I entitle transcendental all knowledge
which is occupied not so much with objects as with the
mode of our knowledge of objects in so far as this mode of
knowledge is to be possible a priori. A system of such 
concepts might be entitled transcendental philosophy. But that
is still, at this stage, too large an undertaking. For since
such a science must contain, with completeness, both kinds
of a priori knowledge, the analytic no less than the synthetic,
it is, so far as our present purpose is concerned, much too
comprehensive. We have to carry the analysis so far only
as is indispensably necessary in order to comprehend, in
their whole extent, the principles of a priori synthesis, with
which alone we are called upon to deal. It is upon this
enquiry, which should be entitled not a doctrine, but only
a transcendental critique, that we are now engaged. Its purpose
is not to extend knowledge, but only to correct it, and to
supply a touchstone of the value, or lack of value, of all a priori
knowledge. Such a critique is therefore a preparation, so far
as may be possible, for an organon; and should this turn out
not to be possible, then at least for a canon, according to which,
in due course, the complete system of the philosophy of pure
reason -- be it in extension or merely in limitation of its 
knowledge -- may be carried into execution, analytically as well as
synthetically. That such a system is possible, and indeed that
it may not be of such great extent as to cut us off from the hope
of entirely completing it, may already be gathered from the
fact that what here constitutes our subject-matter is not the
nature of things, which is inexhaustible, but the understanding
which passes judgment upon the nature of things; and this
understanding, again, only in respect of its a priori knowledge.
These a priori possessions of the understanding, since they
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have not to be sought for without, cannot remain hidden from
of our apprehending them in their completeness of judging
them. Still less may the reader here expect a critique of
books and systems of pure reason; we are concerned only with
the critique of the faculty of pure reason itself. Only in so far
as we build upon this foundation do we have a reliable 
touchstone for estimating the philosophical value of old and new
works in this field. Otherwise the unqualified historian or critic
is passing judgments upon the groundless assertions of others
by means of his own, which are equally groundless.
Transcendental philosophy is only the idea of a science,
for which the critique of pure reason has to lay down the
complete architectonic plan. That is to say, it has to guarantee,
as following from principles, the completeness and certainty
of the structure in all its parts. It is the system of
all principles of pure reason. And if this critique is not
itself to be entitled a transcendental philosophy, it is solely 
because, to be a complete system, it would also have to contain
an exhaustive analysis of the whole of a priori human knowledge.
Our critique must, indeed, supply a complete enumeration
of all the fundamental concepts that go to constitute such
pure knowledge. But it is not required to give an exhaustive
analysis of these concepts, nor a complete review of those
that can be derived from them. Such a demand would be
unreasonable, partly because this analysis would not be
appropriate to our main purpose, inasmuch as there is no
such uncertainty in regard to analysis as we encounter in the
case of synthesis, for the sake of which alone our whole critique
is undertaken; and partly because it would be inconsistent
with the unity of our plan to assume responsibility for the 
completeness of such an analysis and derivation, when in view of our
purpose we can be excused from doing so. The analysis of these
a priori concepts, which later we shall have to enumerate, and
the derivation of other concepts from them, can easily, 
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however, be made complete when once they have been established
as exhausting the principles of synthesis, and if in this 
essential respect nothing be lacking in them.
The critique of pure reason therefore will contain all that
is essential in transcendental philosophy. While it is the 
complete idea of transcendental philosophy, it is not equivalent
to that latter science; for it carries the analysis only so far as
is requisite for the complete examination of knowledge which
is a priori and synthetic.
What has chiefly to be kept in view in the division of such
a science, is that no concepts be allowed to enter which 
contain in themselves anything empirical, or, in other words,
that it consist in knowledge wholly a priori. Accordingly,
although the highest principles and fundamental concepts of
morality are a priori knowledge, they have no place in 
transcendental philosophy, because, although they do not lay at
the foundation of their precepts the concepts of pleasure
and pain, of the desires and inclinations, etc. , all of which
are of empirical origin, yet in the construction of a system
of pure morality these empirical concepts must necessarily
be brought into the concept of duty, as representing either a
hindrance, which we have to overcome, or an allurement, which
must not be made into a motive. Transcendental philosophy is
therefore a philosophy of pure and merely speculative reason.
All that is practical, so far as it contains motives, relates to
feelings, and these belong to the empirical sources of 
knowledge. 
If we are to make a systematic division of the science
which we are engaged in presenting, it must have first a
doctrine of the elements, and secondly, a doctrine of the method
of pure reason. Each of these chief divisions will have its
subdivisions, but the grounds of these we are not yet in a
position to explain. By way of introduction or anticipation
we need only say that there are two stems of human knowledge,
namely, sensibility and understanding, which perhaps
spring from a common, but to us unknown, root. Through the
former, objects are given to us; through the latter, they are
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thought. Now in so far as sensibility may be found to contain
a priori representations constituting the condition under
which objects are given to us, it will belong to transcendental
philosophy. And since the conditions under which alone the
objects of human knowledge are given must precede those
under which they are thought, the transcendental doctrine
of sensibility will constitute the first part of the science of the
elements.