authors of that science remain true to their idea of it; they do not distinguish the motives which are prescribed as such by reason alone altogether a priori, and which are properly moral, from the empirical motives which the understanding raises to general conceptions merely by comparison of experiences; but without noticing the difference of their sources, and looking on them all as homogeneous, they consider only their greater or less amount.  It is in this way they frame their notion of obligation, which though anything but moral, is all that can be asked for in a philosophy which passes no judgment at all on the origin of all possible practical concepts, whether they are a priori, or only a posteriori.

Intending to publish hereafter a metaphysic of morals, I issue in the first instance these fundamental principles.  Indeed there is properly no other foundation for it than the critical examination of a pure practical reason; just as that of metaphysics is the critical examination of the pure speculative reason, already published.  But in the first place the former is not so absolutely necessary as the latter, because in moral concerns human reason can easily be brought to a high degree of correctness and completeness, even in the 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 a 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 gratifying than useful, since the easy applicability of a principle and its apparent adequacy give no very certain proof of its soundness, but rather inspire a certain partiality, which prevents us from examining and estimating it strictly in itself, and without regard to consequences.