f knowledge upon material applied
in experience. He compared himself to Copernicus who had taught men that
they themselves revolved around a central fact of the universe. They had
supposed that the facts revolved about them. The central fact of the
intellectual world is experience. This experience seems to be given us
in the forms of time and space and cause. These are merely forms of the
mind's own activity. It is not possible for us to know 'the thing in
itself,' the _Ding an sich_ in Kant's phrase, which is the external
factor in any sensation or perception. We cannot distinguish that
external factor from the contribution to it, as it stands in our
perception, which our own minds have made. If we cannot do that even for
ourselves, how much less can we do it for others! It is the subject, the
thinking being who says 'I,' which, by means of its characteristic and
necessary active processes, in the perception of things under the forms
of time and space, converts the chaotic material of knowledge into a
regular and ordered world of reasoned experience. In this sense the
understanding itself imposes laws, if not upon nature, yet, at least,
upon nature as we can ever know it. There is thus in Kant's philosophy a
sceptical aspect. Knowledge is limited to phenomena. We cannot by pure
reason know anything of the world which lies beyond experience. This
thought had been put forth by Locke and Berkeley, and by Hume also, in a
different way. But with Kant this scepticism was not the gist of his
philosophy. It was urged rather as the basis of the unconditioned
character which he proposed to assert for the practical reason. Kant's
scepticism is therefore very different from that of Hume. It does not
militate against the profoundest religious conviction. Yet it prepared
the way for some of the just claims of modern agnosticism.

According to Kant, it is as much the province of the practical reason to
lay down laws for action as it is the province of pure reason to
determine the conditions of thought, though the practical reason can
define only the form of action which shall be in the spirit of duty. It
cannot present duty to us as an object of desire. Desire can be only a
form of self-love. In the end it reckons with the advantage of having
done one's duty. It thus becomes selfish and degraded. The
identification of duty and interest was particularly offensive to Kant.
He was at war with every form of hedonism. To do one's duty beca