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 called 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 (Sec. ix.).
This enlargement of the notion of duty beyond that of external freedom and of its limitation by the merely formal condition of its constant harmony; this, I say, in which, instead of constraint from without, there is set up freedom within, the power of self-constraint, and that not by the help of other inclinations, but by pure practical reason (which scorns all such help), consists in this fact, which raises it above juridical duty; that by it ends are proposed from which jurisprudence altogether abstracts. In the case of the moral imperative, and the supposition of freedom which it necessarily involves, the law, the power (to fulfil it) and the rational will that determines the maxim, constitute all the elements that form the notion of juridical duty. But in the imperative, which commands the duty of virtue, there is added, besides the notion of self-constraint, that of an end; not one that we have, but that we ought to have, which, therefore, pure practical reason has in itself, whose highest, unconditional end (which, however, continues to be duty) consists in this: that virtue is its own end and, by deserving well of men, is also its own reward. Herein it shines so brightly as an ideal to human perceptions, it seems to cast in the shade even holiness itself, which is never tempted to transgression. * This, however, is an illusion arising from the fact that as we have no measure for the degree of strength, except the greatness of the obstacles which might have been overcome (which in our case are the inclinations), we are led to mistake the subjective conditions of estimation of a magnitude for the objective conditions of the magnitude itself. But when compared with human ends, all of which have their obstacles to be overcome, it is true that the worth of virtue itself, which is its own end, far outweighs the worth of all the utility and all the empirical ends and advantages which it may have as consequences.