eing conceptions proper, he is necessarily led to
hold that an appeal to experience is needed in order to establish the
reality of a corresponding object. Yet, this being so, he should have
asked himself whether, without an appeal to perception, we could even
say that a corresponding object was possible. That he did not ask this
question is partly due to the fact that he attributes the form and the
matter of knowledge to different sources, viz. to the mind and to
things in themselves. While the conceptions involved in the forms of
perception, space, and time, and also the categories are the
manifestations of the mind's own nature, sensations, which form the
matter of knowledge, are due to the action of things in themselves on
our sensibility, and of this activity we can say nothing. Hence, from
the point of view of our mind--and since we do not know things in
themselves, this is the only point of view we can take--the existence
of sensations, and therefore of objects, which must be given in
perception, is wholly contingent and only to be discovered through
experience. On the other hand, since the forms of perception and
conception necessarily determine in certain ways the nature of
objects, _if_ there prove to be any objects, the conceptions involved
may be thought to determine what objects are possible, even though the
very existence of the objects is uncertain. Nevertheless, on his own
principles, Kant should have allowed that, apart from perception, we
could discover _a priori_ at least the reality, even if not the
necessity, of the objects of these conceptions. For his general view
is that the forms of perception and the categories are only actualized
on the occasion of the stimulus afforded by the action of things in
themselves on the sensibility. Hence the fact that the categories and
forms of perception are actualized--a fact implied in the very
existence of the _Critique_--involves the existence of objects
corresponding to the categories and to the conceptions involved in the
forms of perception. On Kant's own principles, therefore, we could say
_a priori_ that there must be objects corresponding to these
conceptions, even though their nature in detail could only be filled
in by experience.[14]

[14] Cf. Caird, i. 604-5.

NOTE ON THE REFUTATION OF IDEALISM

This well-known passage[1] practically replaces a long section,[2]
contained only in the first edition, on the fourth paralogism of
pure reas