priori, I must presuppose in myself laws of the understanding which
are expressed in conceptions a priori. To these conceptions, then,
all the objects of experience must necessarily conform. Now there are
objects which reason thinks, and that necessarily, but which cannot
be given in experience, or, at least, cannot be given so as reason
thinks them. The attempt to think these objects will hereafter furnish
an excellent test of the new method of thought which we have adopted,
and which is based on the principle that we only cognize in things
a priori that which we ourselves place in them.*

[*Footnote: This method, accordingly, which we have borrowed from the
natural philosopher, consists in seeking for the elements of pure reason
in that which admits of confirmation or refutation by experiment. Now
the propositions of pure reason, especially when they transcend the
limits of possible experience, do not admit of our making any experiment
with their objects, as in natural science. Hence, with regard to those
conceptions and principles which we assume a priori, our only course
ill be to view them from two different sides. We must regard one and
the same conception, on the one hand, in relation to experience as
an object of the senses and of the understanding, on the other hand,
in relation to reason, isolated and transcending the limits of
experience, as an object of mere thought. Now if we find that, when
we regard things from this double point of view, the result is in harmony
with the principle of pure reason, but that, when we regard them
from a single point of view, reason is involved in self-contradiction,
then the experiment will establish the correctness of this
distinction.]

This attempt succeeds as well as we could desire, and promises to
metaphysics, in its first part--that is, where it is occupied with