to prove that the very conception is an
empty one. His reasonings seem to result in the conclusion that we can
make no intelligible statement about things so cut off from our
experience as noumena are supposed to be; and one would imagine that he
would have felt impelled to go on to the frank declaration that we have
no reason to believe in noumena at all, and had better throw away
altogether so meaningless and useless a notion. But he was a
conservative creature, and he did not go quite so far.

So far there is little choice between Kant and Hume. Certainly the
former does not appear to have rehabilitated the external world which
had suffered from the assaults of his predecessors. What important
difference is there between his doctrine and that of the man whose
skeptical tendencies he wished to combat?

The difference is this: Descartes and Locke had accounted for our
knowledge of things by maintaining that things act upon us, and make an
impression or sensation--that their action, so to speak, begets ideas.
This is a very ancient doctrine as well as a very modern one; it is the
doctrine that most men find reasonable even before they devote
themselves to the study of philosophy. The totality of such
impressions received from the external world, they are accustomed to
regard as our _experience_ of external things; and they are inclined to
think that any knowledge of external things not founded upon experience
can hardly deserve the name of knowledge.

Now, Hume, when he cast doubt upon the existence of external things,
did not, as I have said above, divest himself of the suggestions of the
word "impression." He insists strenuously that all our knowledge is
founded upon experience; and he holds that no experience can give us
knowledge that is necessary and universal. We know things as they are
revealed to us in our experience; but who can guarantee that we may not
have new experiences of a quite different kind, and which flatly
contradict the notions which we have so far attained of what is
possible and impossible, true and untrue.

It is here that Kant takes issue with Hume. A survey of our knowledge
makes clear, he thinks, that we are in the possession of a great deal
of information that is not of the unsatisfactory kind that, according
to Hume, all our knowledge of things must be. There, for example, are
all the truths of mathematics. When we enunciate a truth regarding the
relations of the lines and an