insisting that such proposition a priori was impossible. According
to his conclusions, then, all that we term metaphysical science is
a mere delusion, arising from the fancied insight of reason into that
which is in truth borrowed from experience, and to which habit has
given the appearance of necessity. Against this assertion, destructive
to all pure philosophy, he would have been guarded, had he had our
problem before his eyes in its universality. For he would then have
perceived that, according to his own argument, there likewise could
not be any pure mathematical science, which assuredly cannot exist
without synthetical propositions a priori--an absurdity from which
his good understanding must have saved him.

In the solution of the above problem is at the same time
comprehended the possibility of the use of pure reason in the
foundation and construction of all sciences which contain
theoretical knowledge a priori of objects, that is to say, the
answer to the following questions:

How is pure mathematical science possible?

How is pure natural science possible?

Respecting these sciences, as they do certainly exist, it may with
propriety be asked, how they are possible?--for that they must be
possible is shown by the fact of their really existing.* But as to
metaphysics, the miserable progress it has hitherto made, and the fact
that of no one system yet brought forward, far as regards its true
aim, can it be said that this science really exists, leaves any one
at liberty to doubt with reason the very possibility of its existence.