PROLEGOMENA TOANYFUTUREMETAPHYSICS 819
Metaphysics has to do not only with concepts of nature, which always find their
application in experience, but also with pure rational concepts, which never can be
given in any possible experience whatever. Consequently it deals with concepts whose
objective reality (namely, that they are not mere chimeras) and with assertions whose
truth or falsity cannot be discovered or confirmed by any experience. This part of
metaphysics, however, is precisely what constitutes its essential end, to which the rest is
only a means, and thus this science is in need of such a deduction for its own sake. The
third question now proposed relates therefore as it were to the root and peculiarity of
metaphysics, that is, the occupation of reason merely with itself and the supposed
knowledge of objects arising immediately from this brooding over its own concepts,
without requiring, or indeed being able to reach that knowledge through, experience.*
Without solving this problem, reason can never satisfy itself. The empirical use to
which reason limits the pure understanding does not fully satisfy the proper calling of
reason. Every single experience is only a part of the whole sphere of its domain, but the
absolute totality of all possible experience is itself not experience. Yet it is a necessary
problem for reason, the mere representation of which requires concepts quite different
from the pure concepts of the understanding, whose use is only immanent,or refers to
experience, so far as it can be given. Whereas the concepts of reason aim at the complete-
ness, that is, the collective unity of all possible experience, and thereby transcend every
given experience. Thus they become transcendent.
As the understanding stands in need of categories for experience, reason contains
in itself the source of Ideas, by which I mean necessary concepts whose object cannot
be given in any experience. The latter are inherent in the nature of reason, as the former
are in that of the understanding. While the former carry with them an illusion likely to
mislead, the illusion of the latter is inevitable, though it certainly can be kept from
misleading us.
Since all illusion consists in holding the subjective ground of our judgments to be
objective, a self-knowledge of pure reason in its transcendent (presumptuous) use is the
sole preservative from the aberrations into which reason falls when it mistakes its
calling and transcendently refers to the object that which concerns only its own subject
and its guidance in all immanent use.
§ 41. The distinction of Ideas—that is, of pure concepts of reason—from
categories, or pure concepts of the understanding, as cognitions of a quite distinct
species, origin, and use, is so important a point in founding a science which is to contain
the system of all these a prioricognitions that, without this distinction, metaphysics is
absolutely impossible or is at best a random, bungling attempt to build a castle in the air
without a knowledge of the materials or of their fitness for this or any purpose. Had the
Critique of Pure Reasondone nothing but first point out this distinction, it would
thereby have contributed more to clear up our conception of, and to guide our inquiry
in, the field of metaphysics than all the vain efforts which had hitherto been made to
satisfy the transcendent problems of pure reason, but which had never surmised that we
were in quite another field than that of the understanding, and hence classed concepts of
the understanding and those of reason together as if they were of the same kind.
§ 42. All pure cognitions of the understanding have this feature that their concepts
present themselves in experience, and their principles can be confirmed by it; whereas
328329*If we can say that a science is actual, at least in the idea of all men, as soon as it appears that the
problems which lead to it are proposed to everybody by the nature of human reason, and that therefore many
(though faulty) endeavors are unavoidably made in its behalf, then we are bound to say that metaphysics is
subjectively (and indeed necessarily) actual, and therefore, we justly ask, how is it (objectively) possible.