III.: of the subdivision of a metaphysic of morals.

All legislation (whether it prescribes internal or external actions, and these either à priori by pure reason or by the will of another) involves two things: first, a law, which objectively presents the action that is to be done as necessary, i. e. makes it a duty; secondly, a spring, which subjectively connects with the idea of the law the motive determining the elective will to this action; hence, the second element is this, that the law makes duty the spring. By the former the action is presented as duty, and this is a mere theoretical knowledge of the possible determination of the elective will, i. e. of practical rules; by the latter, the obligation so to act is connected with a motive which determines the elective will generally in the agent.

Accordingly, all legislation may be divided into two classes in respect of the springs employed (and this whether the actions prescribed are the same or not: as, for instance, the actions might be in all cases external) . That legislation which at once makes an action a duty, and makes this duty the spring, is ethical. That which does not include the latter in the law, and therefore admits a spring different from the idea of duty itself, is juridical. As regards the latter, it is easily seen that this spring, which is distinct from the idea of duty, must be derived from the pathological motives of choice, namely, the inclinations and aversions, and amongst these from the latter, since it is a legislation, which must be constraining, not an invitation, which is persuasive.

The mere agreement or disagreement of an action with the law, without regard to the motive from which the action springs, is called legality; but when the idea of duty arising from the law is also the motive of the action, the agreement is called the morality of the action.

Duties arising from forensic legislation can only be external duties, because this legislation does not require that the idea of this duty, which is internal, shall be of itself the motive of the elective will of the agent; and as it, nevertheless, requires a suitable spring, it can only connect external springs with the law. On the other hand, ethical legislation, while it makes internal actions duties, does not exclude external actions, but applies generally to everything that is duty. But just because ethical legislation includes in its law the inner spring of the action (the idea of duty), a property which cannot belong to the external legislation; hence ethical legislation cannot be external (not even that of a divine will), although it may adopt duties which rest on external legislation, and take them regarded as duties into its own legislation as springs of action.

From hence we may see that all duties belong to Ethics, simply because they are duties; but it does not follow that their legislation is always included in Ethics: in the case of many duties it is quite outside Ethics. Thus Ethics requires that I should fulfil my pledged word, even though the other party could not compel me to do so; but the law (pacta sunt servanda) and the corresponding duty are taken by Ethics from jurisprudence. Accordingly, it is not in Ethics but in Jus that the legislation is contained which enjoins that promises be kept. Ethics teaches only that even if the spring were absent which is connected by forensic legislation with that duty, namely, external compulsion, yet the idea of duty would alone be sufficient as a spring. For if this were not so, and if the legislation itself were not forensic, and the duty arising from it not properly a legal duty (in contrast to a moral duty), then faithfulness to one’s engagements would be put in the same class as actions of benevolence and the obligation to them, which cannot be admitted. It is not an ethical duty to keep one’s promise, but a legal duty, one that we can be compelled to perform. Nevertheless, it is a virtuous action (a proof of virtue) to do so, even where no compulsion is to be apprehended. Law and morals, therefore, are distinguished not so much by the diversity of their duties, but rather by the diversity of the legislation which connects this or that motive with the law.

Ethical legislation is that which cannot be external (although the duties may be external); forensic legislation is that which can be external. Thus to keep one’s contract is an external duty; but the command to do this merely because it is a duty, without regard to any other motive, belongs only to the internal legislation. Accordingly, the obligation is reckoned as belonging to Ethics, not as being a special kind of duty (a special kind of actions to which one is bound)—for in Ethics as well as in law we have external duties—but because in the supposed case the legislation is an internal one, and can have no external lawgiver. For the same reason duties of benevolence, although they are external duties (obligations to external actions), are yet reckoned as belonging to Ethics because the legislation imposing them can only be internal. No doubt Ethics has also duties peculiar to itself (ex. gr. duties to ourselves), but it also has duties in common with law, only the kind of obligation is different. For it is the peculiarity of ethical legislation to perform actions solely because they are duties, and to make the principle of duty itself the adequate spring of the will, no matter whence the duty may be derived. Hence, while there are many directly ethical duties, the internal legislation makes all others indirectly ethical.