commonest understanding, while on the contrary in its theoretic but
pure use it is wholly dialectical; and in the second place if the
critique of a pure practical reason is to be complete, it must be
possible at the same time to show its identity with the speculative
reason in a common principle, for it can ultimately be only one and
the same reason which has to be distinguished merely in its
application. I could not, however, bring it to such completeness here,
without introducing considerations of a wholly different kind, which
would be perplexing to the reader. On this account I have adopted
the title of Fundamental Principles of the Metaphysic of Morals
instead of that of a Critical Examination of the pure practical
reason.

But in the third place, since a metaphysic of morals, in spite of
the discouraging title, is yet capable of being presented in popular
form, and one adapted to the common understanding, I find it useful to
separate from it this preliminary treatise on its fundamental
principles, in order that I may not hereafter have need to introduce
these necessarily subtle discussions into a book of a more simple
character.

The present treatise is, however, nothing more than the
investigation and establishment of the supreme principle of
morality, and this alone constitutes a study complete in itself and
one which ought to be kept apart from every other moral investigation.
No doubt my conclusions on this weighty question, which has hitherto
been very unsatisfactorily examined, would receive much light from the
application of the same principle to the whole system, and would be
greatly confirmed by the adequacy which it exhibits throughout; but
I must forego this advantage, which indeed would be after all more