reason for such an undertaking.

Now the safe ground of experience being thus abandoned, it seems
nevertheless natural that we should hesitate to erect a building
with the cognitions we possess, without knowing whence they come,
and on the strength of principles, the origin of which is
undiscovered. Instead of thus trying to build without a foundation,
it is rather to be expected that we should long ago have put the
question, how the understanding can arrive at these a priori
cognitions, and what is the extent, validity, and worth which they
may possess? We say, "This is natural enough," meaning by the word
natural, that which is consistent with a just and reasonable way of
thinking; but if we understand by the term, that which usually
happens, nothing indeed could be more natural and more
comprehensible than that this investigation should be left long
unattempted. For one part of our pure knowledge, the science of
mathematics, has been long firmly established, and thus leads us to
form flattering expectations with regard to others, though these may
be of quite a different nature. Besides, when we get beyond the bounds
of experience, we are of course safe from opposition in that
quarter; and the charm of widening the range of our knowledge is so
great that, unless we are brought to a standstill by some evident
contradiction, we hurry on undoubtingly in our course. This,
however, may be avoided, if we are sufficiently cautious in the
construction of our fictions, which are not the less fictions on
that account.

Mathematical science affords us a brilliant example, how far,
independently of all experience, we may carry our a priori
knowledge. It is true that the mathematician occupies himself with