But it does not follow that everything the doing of which is virtue, is, properly speaking, a duty of virtue.  The former may concern merely the form of the maxims; the latter applies to the matter of them, namely, to an end which is also conceived as duty.  Now, as the ethical obligation to ends, of which there may be many, is only indeterminate, because it contains only a law for the maxim of actions, and the end is the matter (object) of elective will; hence there are many duties, differing according to the difference of lawful ends, which may be called duties of virtue (officia honestatis), just because they are subject only to free self-constraint, not to the constraint of other men, and determine the end which is also a duty.

Virtue, being a coincidence of the rational will, with every duty firmly settled in the character, is, like everything formal, only one and the same.  But, as regards the end of actions, which is also duty, that is, as regards the matter which one ought to make an end, there may be several virtues; and as the obligation to its maxim is called a duty of virtue, it follows that there are also several duties of virtue.

{Introduction ^paragraph 90}

The supreme principle of ethics (the doctrine of virtue) is:  “Act on a maxim, the ends of which are such as it might be a universal law for everyone to have.”  On this principle a man is an end to himself as well as others, and it is not enough that he is not permitted to use either himself or others merely as means (which would imply that be might be indifferent to them), but it is in itself a duty of every man to make mankind in general his end.

The principle of ethics being a categorical imperative does not admit of proof, but it admits of a justification from principles of pure practical reason.  Whatever in relation to mankind, to oneself, and others, can be an end, that is an end for pure practical reason:  for this is a faculty of assigning ends in general; and to be indifferent to them, that is, to take no interest in them, is a contradiction; since in that case it would not determine the maxims of actions (which always involve an end), and consequently would cease to be practical reasons.  Pure reason, however, cannot command any ends a priori, except so far as it declares the same to be also a duty, which duty is then cared a duty of virtue.

X. The Supreme Principle of Jurisprudence was Analytical; that of

Ethics is Synthetical

{Introduction ^paragraph 95}

That external constraint, so far as it withstands that which hinders the external freedom that agrees with general laws (as an obstacle of the obstacle thereto), can be consistent with ends generally, is clear on the principle of contradiction, and I need not go beyond the notion of freedom in order to see it, let the end which each may be what he will.  Accordingly, the supreme principle of jurisprudence is an analytical principle.  On the contrary the principle of ethics goes beyond the notion of external freedom and, by general laws, connects further with it an end which it makes a duty.  This principle, therefore, is synthetic.  The possibility of it is contained in the deduction (SS ix).