It is usual to designate Kant as the founder of the Theory of
Knowledge in the modern sense. Against this view it might plausibly
be argued that the history of philosophy records prior to Kant
numerous investigations which deserve to be regarded as something
more than mere beginnings of such a science. Thus Volkelt, in his
fundamental work on the Theory of Knowledge, [16] remarks that the
critical treatment of this discipline took its origin already with
Locke. But in the writings of even older philosophers, yes, even in
the philosophy of Ancient Greece, discussions are to be found which
at the present day are usually undertaken under the heading of Theory
of Knowledge. However, Kant has revolutionised all problems under this
head from their very depths up, and, following him, numerous thinkers
have worked them through so thoroughly that all the older attempts at
solutions may be found over again either in Kant himself or else in
his successors. Hence, for the purposes of a purely systematic, as
distinct from a historical, study of the Theory of Knowledge, there
is not much danger of omitting any important phenomenon by taking
account only of the period since Kant burst upon the world with his
Critique of Pure Reason. All previous epistemological achievements
are recapitulated during this period.
The fundamental question of Kant's Theory of Knowledge is, How are
synthetic judgments a priori possible? Let us consider this question
for a moment in respect of its freedom from presuppositions. Kant
asks the question precisely because he believes that we can attain
unconditionally certain knowledge only if we are able to prove
the validity of synthetic judgments a priori. He says: "Should this
question be answered in a satisfactory way, we shall at the same time
learn what part reason plays in the foundation and completion of those
sciences which contain a theoretical a priori knowledge of objects;"
[17] and, further, "Metaphysics stands and falls with the solution of
this problem, on which, therefore, the very existence of Metaphysics
absolutely depends." [18]
Are there any presuppositions in this question, as formulated by
Kant? Yes, there are. For the possibility of a system of absolutely
certain knowledge is made dependent on its being built up exclusively
out of judgments which are synthetic and acquired independently of
all experience. "Synthetic" is Kant's term for judgments in which
the concept of the predicate adds to the concept of the subject
something which lies wholly outside the subject, "although it stands
in some connection with the subject," [19] whereas in "analytic"
judgments the predicate affirms only what is already (implicitly)
contained in the subject. This is not the place for considering the
acute objections which Johannes Rehmke [20] brings forward against
this classification of judgments. For our present purpose, it is
enough to understand that we can attain to genuine knowledge only
through judgments which add to one concept another the content of
which was not, for us at least, contained in that of the former. If
we choose to call this class of judgments, with Kant, "synthetic," we
may agree that knowledge in judgment form is obtainable only where the
connection of predicate and subject is of this synthetic sort. But,
the case is very different with the second half of Kant's question,
which demands that these judgments are to be formed a priori, i.e.,
independently of all experience. For one thing, it is altogether
possible [21] that such judgments do not occur at all. At the start
of the Theory of Knowledge we must hold entirely open the question,
whether we arrive at any judgments otherwise than by experience, or
only by experience. Indeed, to unprejudiced reflection the alleged
independence of experience seems from the first to be impossible. For,
let the object of our knowledge be what it may--it must, surely, always
present itself to us at some time in an immediate and unique way; in
short, it must become for us an experience. Mathematical judgments,
too, are known by us in no other way than by our experiencing them
in particular concrete cases. Even if, with Otto Liebmann, [22] for
example, we treat them as founded upon a certain organisation of our
consciousness, this empirical character is none the less manifest. We
shall then say that this or that proposition is necessarily valid,
because the denial of its truth would imply the denial of our
consciousness, but the content of a proposition can enter our knowledge
only by its becoming an experience for us in exactly the same way in
which a process in the outer world of nature does so. Let the content
of such a proposition include factors which guarantee its absolute
validity, or let its validity be based on other grounds--in either
case, I can possess myself of it only in one way and in no other:
it must be presented to me in experience. This is the first objection
to Kant's view.
The other objection lies in this, that we have no right, at the outset
of our epistemological investigations, to affirm that no absolutely
certain knowledge can have its source in experience. Without doubt,
it is easily conceivable that experience itself might contain a
criterion guaranteeing the certainty of all knowledge which has an
empirical source.
Thus, Kant's formulation of the problem implies two
presuppositions. The first is that we need, over and above experience,
another source of cognitions. The second is that all knowledge from
experience has only conditional validity. Kant entirely fails to
realise that these two propositions are open to doubt, that they stand
in need of critical examination. He takes them over as unquestioned
assumptions from the dogmatic philosophy of his predecessors and makes
them the basis of his own critical inquiries. The dogmatic thinkers
assume the validity of these two propositions and simply apply them in
order to get from each the kind of knowledge which it guarantees. Kant
assumed their validity and only asks, What are the conditions of
their validity? But, what if they are not valid at all? In that case,
the edifice of Kantian doctrine lacks all foundation whatever.
The whole argumentation of the five sections which precede Kant's
formulation of the problem, amounts to an attempt to prove that the
propositions of Mathematics are synthetic. [23] But, precisely the
two presuppositions which we have pointed out are retained as mere
assumptions in his discussions. In the Introduction to the Second
Edition of the Critique of Pure Reason we read, "experience can tell us
that a thing is so and so, but not that it cannot be otherwise," and,
"experience never bestows on its judgments true or strict universality,
but only the assumed and relative universality of induction." [24]
In Prologomena, [25] we find it said, "First, as regards the sources
of metaphysics, the very concept of Metaphysics implies that they
cannot be empirical. The principles of Metaphysics (where the term
'principles' includes, not merely its fundamental propositions, but
also its fundamental concepts), can never be gained from experience,
for the knowledge of the metaphysician has precisely to be, not
physical, but 'metaphysical,' i.e., lying beyond the reach of
experience." Lastly Kant says in the Critique of Pure Reason: "The
first thing to notice is, that no truly mathematical judgments are
empirical, but always a priori. They carry necessity on their very
face, and therefore cannot be derived from experience. Should anyone
demur to this, I am willing to limit my assertion to the propositions
of Pure Mathematics, which, as everybody will admit, are not empirical
judgments, but perfectly pure a priori knowledge." [26]
We may open the Critique of Pure Reason wherever we please, we shall
always find that in all its discussions these two dogmatic propositions
are taken for granted. Cohen [27] and Stadler [28] attempt to prove
that Kant has established the a priori character of the propositions
of Mathematics and Pure Natural Science. But all that Kant tries to do
in the Critique may be summed up as follows. The fact that Mathematics
and Pure Natural Science are a priori sciences implies that the "form"
of all experience has its ground in the subject. Hence, all that is
given by experience is the "matter" of sensations. This matter is
synthesised by the forms, inherent in the mind, into the system of
empirical science. It is only as principles of order for the matter
of sense that the formal principles of the a priori theories have
function and significance. They make empirical science possible, but
they cannot transcend it. These formal principles are nothing but the
synthetic judgments a priori, which therefore extend, as conditions
of all possible empirical knowledge, as far as that knowledge but no
further. Thus, the Critique of Pure Reason, so far from proving the
a priori character of Mathematics and Pure Natural Science, does but
delimit the sphere of their applicability on the assumption that their
principles must become known independently of experience. Indeed,
Kant is so far from attempting a proof of the a priori character of
these principles, that he simply excludes that part of Mathematics
(see the quotation above) in which, even according to his view, that
character might be called in question, and confines himself to the part
in which he thinks he can infer the a priori character from the bare
concepts involved. Johannes Volkelt, too, comes to the conclusion that
"Kant starts from the explicit presupposition" that "there actually
does exist knowledge which is universal and necessary." He goes
on to remark, "This presupposition which Kant has never explicitly
questioned, is so profoundly contradictory to the character of a truly
critical Theory of Knowledge, that the question must be seriously put
whether the Critique is to be accepted as critical Theory of Knowledge
at all." Volkelt does, indeed, decide that there are good grounds for
answering this question in the affirmative, but still, as he says,
"this dogmatic assumption does disturb the critical attitude of
Kant's epistemology in the most far-reaching way." [29] In short,
Volkelt, too, finds that the Critique of Pure Reason is not a Theory
of Knowledge free from all assumptions.
In substantial agreement with our view are also the views of
O. Liebmann, [30] Holder, [31] Windelband, [32] Ueberweg, [33] Eduard
von Hartmann, [34] and Kuno Fischer, [35] all of whom acknowledge
that Kant makes the a priori character of Pure Mathematics and Physics
the basis of his whole argumentation.
The propositions that we really have knowledge which is independent
of all experience, and that experience can furnish knowledge of
only relative universality, could be accepted by us as valid only
if they were conclusions deduced from other propositions. It would
be absolutely necessary for these propositions to be preceded by an
inquiry into the essential nature of experience, as well as by another
inquiry into the essential nature of knowing. The former might justify
the first, the latter the second, of the above two propositions.
It would be possible to reply to the objections which we have urged
against the Critique of Pure Reason, as follows. It might be said
that every Theory of Knowledge must first lead the reader to the
place where the starting-point, free from all presuppositions, is to
be found. For, the knowledge which we have at any given moment of our
lives is far removed from this starting-point, so that we must first
be artificially led back to it. Now, it is true that some such mutual
understanding between author and reader concerning the starting-point
of the science is necessary in all Theory of Knowledge. But such an
understanding ought on no account to go beyond showing how far the
alleged starting-point of knowing is truly such. It ought to consist of
purely self-evident, analytic propositions. It ought not to lay down
any positive, substantial affirmations which influence, as in Kant,
the content of the subsequent argumentation. Moreover, it is the duty
of the epistemologist to show that the starting-point which he alleges
is really free from all presuppositions. But all this has nothing to
do with the essential nature of that starting-point. It lies wholly
outside the starting-point and makes no affirmations about it. At the
beginning of mathematical instruction, too, the teacher must exert
himself to convince the pupil of the axiomatic character of certain
principles. But no one will maintain that the content of the axioms is
in any way made dependent on these prior discussions of their axiomatic
character. [36] In exactly the same way, the epistemologist, in his
introductory remarks, ought to show the method by which we can reach
a starting-point free from all presuppositions. But the real content
of the starting-point ought to be independent of the reflections by
which it is discovered. There is, most certainly, a wide difference
between such an introduction to the Theory of Knowledge and Kant's way
of beginning with affirmations of quite definite, dogmatic character.