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THE CRITIQUE OF PURE REASON
Of the difference between Pure and Empirical
Knowledge
In Sixteen Parts
Immanuel Kant
Immanuel Kant was born in the East Prussian
city of Königsberg, studied at its university,
and worked there as a tutor and professor
for more than forty years, never travelling
more than fifty miles from home. Although
his outward life was one of legendary calm
and regularity, Kant's intellectual work
easily justified his own claim to have effected
a Copernican revolution in philosophy. Beginning
with his Inaugural Dissertation (1770) on
the difference between right- and left-handed
spatial orientations, Kant patiently worked
out the most comprehensive and influential
philosophical programme of the modern era.
His central thesis-that the possibility of
human knowledge presupposes the active participation
of the human mind-is deceptively simple,
but the details of its application are notoriously
complex.
INTRODUCTION
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 antecedeno 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. For it 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 empirical, which has its sources a posteriori,
that is, in experience.
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,
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 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 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 physics; 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 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 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 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. From the start
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. But the concept
of a 'cause' lies entirely outside the other
concept, and signifies something different
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.
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 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 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. physics, 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 unable
to follow us, as, for instance, in the proposition,
that the world must have a first beginning,
and such like. Thus physics 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 physics 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 physics.
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 physics 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 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.
[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.]
But the poor progress which has hitherto
been made in physics, and the fact that no
system yet propounded can, in view of the
essential purpose of physics, 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, physics actually exists, if not as a
science, yet still as natural disposition
(physica 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
physics. And so we have the question:
How is physics, 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?
But since all attempts which have hitherto
been made to answer these natural questions
-- for instance, whether the world has a
beginning or is from eternity -- have always
met with unavoidable contradictions, we cannot
rest satisfied with the mere natural disposition
to physics, that is, with the pure faculty
of reason itself, from which, indeed, some
sort of physics (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 physics, 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 physics, 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 physic 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, physics 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 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 physical 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 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.
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 have not to be sought for without,
cannot remain hidden from of our apprehending
them in their completeness of judging as
to their value or lack of value, and so of
rightly appraising 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,
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 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.
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