uty of
keeping a promise, he contrasts, at the close of the section, the all
but infallibility of common human reason in practice with its
helplessness in speculation. Notwithstanding, it finds itself unable to
settle the contending claims of Reason and Inclination, and so is
driven to devise a practical philosophy, owing to the rise of a
'Natural Dialectic' or tendency to refine upon the strict laws of duty
in order to make them more pleasant. But, as in the speculative region,
the Dialectic cannot be properly got rid of without a complete Critique
of Reason.

In Section II. the passage is made from the popular moral philosophy
thus arising to the metaphysic of morals. He denies that the notion of
duty that has been taken above from common sage is empirical. It is
proved not to be such from the very assertions of philosophers that men
always act from more or less refined self-love; assertions that are
founded upon the difficulty of proving that acts most apparently
conformed to duty are really such. The fact is, no act _can_ be proved
by experience to be absolutely moral, _i.e._, done solely from regard
to duty, to the exclusion of all inclination; and therefore to concede
that morality and duty are ideas to be had from experience, is the
surest way to get rid of them altogether. Duty, and respect for its
law, are not to be preserved at all, unless Reason is allowed to lay
_absolute_ injunctions on the will, whatever experience says of their
non-execution. How, indeed, is experience to disclose a moral law,
that, in applying to all rational beings as well as men, and to men
only as rational, must originate _a priori_ in pure (practical) Reason?
Instead of yielding the principles of morality, empirical examples of
moral conduct have rather to be judged by these.

All supreme principles of morality, that are genuine, must rest on pure
Reason solely; and the mistake of the popular practical philosophies in
vogue, one and all--whether advancing as their principle a special
determination of human nature, or Perfection, or Happiness, or Moral
Feeling, or Fear of God, or a little of this and a little of that--is
that there has been no previous consideration whether the principles of
morality are to be sought for in our empirical knowledge of human
nature at all. Such consideration would have shown them to be
altogether _a priori_, and would have appeared as a _pure_ practical
philosophy or metaphysic of morals (upon the com