Such a metaphysic of morals, completely isolated, not mixed with any anthropology, theology, physics, or hyperphysics, and still less with occult qualities (which we might call hypophysical), is not only an indispensable substratum of all sound theoretical knowledge of duties, but is at the same time a desideratum of the highest importance to the actual fulfilment of their precepts. For the pure conception of duty, unmixed with any foreign addition of empirical attractions, and, in a word, the conception of the moral law, exercises on the human heart, by way of reason alone (which first becomes aware with this that it can of itself be practical), an influence so much more powerful than all other springs4 which may be derived from the field of experience, that, in the consciousness of its worth, it despises the latter, and can by degrees become their master; whereas a mixed ethics, compounded partly of motives drawn from feelings and inclinations, and partly also of conceptions of reason, must make the mind waver between motives which cannot be brought under any principle, which lead to good only by mere accident and very often also to evil.
From what has been said, it is clear that all moral conceptions have their seat and origin completely a priori in the reason, and that, moreover, in the commonest reason just as truly as in that which is in the highest degree speculative; that they cannot be obtained by abstraction from any empirical, and therefore merely contingent, knowledge; that it is just this purity of their origin that makes them worthy to serve as our supreme practical principle, and that just in proportion as we add anything empirical, we detract from their genuine influence and from the absolute value of actions; that it is not only of the greatest necessity, in a purely speculative point of view, but is also of the greatest practical importance, to derive these notions and laws from pure reason, to present them pure and unmixed, and even to determine the compass of this practical or pure rational knowledge, i.e., to determine the whole faculty of pure practical reason; and, in doing so, we must not make its principles dependent on the particular nature of human reason, though in speculative philosophy this may be permitted, or may even at times be necessary; but since moral laws ought to hold good for every rational creature, we must derive them from the general concept of a rational being. In this way, although for its application to man morality has need of anthropology, yet, in the first instance, we must treat it independently as pure philosophy, i.e., as metaphysic, complete in itself (a thing which in such distinct branches of science is easily done); knowing well that unless we are in possession of this, it would not only be vain to determine the moral element of duty in right actions for purposes of speculative criticism, but it would be impossible to base morals on their genuine principles, even for common practical purposes, especially of moral instruction, so as to produce pure moral dispositions, and to engraft them on men's minds to the promotion of the greatest possible good in the world.
But in order that in this study we may not merely advance by the natural steps from the common moral judgement (in this case very worthy of respect) to the philosophical, as has been already done, but also from a popular philosophy, which goes no further than it can reach by groping with the help of examples, to metaphysic (which does allow itself to be checked by anything empirical and, as it must measure the whole extent of this kind of rational knowledge, goes as far as ideal conceptions, where even examples fail us), we must follow and clearly describe the practical faculty of reason, from the general rules of its determination to the point where the notion of duty springs from it.
Everything in nature works according to laws. Rational beings alone have the faculty of acting according to the conception of laws, that is according to principles, i.e., have a will. Since the deduction of actions from principles requires reason, the will is nothing but practical reason. If reason infallibly determines the will, then the actions of such a being which are recognised as objectively necessary are subjectively necessary also, i.e., the will is a faculty to choose that only which reason independent of inclination recognises as practically necessary, i.e., as good. But if reason of itself does not sufficiently determine the will, if the latter is subject also to subjective conditions (particular impulses) which do not always coincide with the objective conditions; in a word, if the will does not in itself completely accord with reason (which is actually the case with men), then the actions which objectively are recognised as necessary are subjectively contingent, and the determination of such a will according to objective laws is obligation, that is to say, the relation of the objective laws to a will that is not thoroughly good is conceived as the determination of the will of a rational being by principles of reason, but which the will from its nature does not of necessity follow.
The conception of an objective principle, in so far as it is obligatory for a will, is called a command (of reason), and the formula of the command is called an imperative.
All imperatives are expressed by the word ought [or shall], and thereby indicate the relation of an objective law of reason to a will, which from its subjective constitution is not necessarily determined by it (an obligation). They say that something would be good to do or to forbear, but they say it to a will which does not always do a thing because it is conceived to be good to do it. That is practically good, however, which determines the will by means of the conceptions of reason, and consequently not from subjective causes, but objectively, that is on principles which are valid for every rational being as such. It is distinguished from the pleasant, as that which influences the will only by means of sensation from merely subjective causes, valid only for the sense of this or that one, and not as a principle of reason, which holds for every one.5
A perfectly good will would therefore be equally subject to objective laws (viz., laws of good), but could not be conceived as obliged thereby to act lawfully, because of itself from its subjective constitution it can only be determined by the conception of good. Therefore no imperatives hold for the Divine will, or in general for a holy will; ought is here out of place, because the volition is already of itself necessarily in unison with the law. Therefore imperatives are only formulae to express the relation of objective laws of all volition to the subjective imperfection of the will of this or that rational being, e.g., the human will.
Now all imperatives command either hypothetically or categorically. The former represent the practical necessity of a possible action as means to something else that is willed (or at least which one might possibly will). The categorical imperative would be that which represented an action as necessary of itself without reference to another end, i.e., as objectively necessary.
Since every practical law represents a possible action as good and, on this account, for a subject who is practically determinable by reason, necessary, all imperatives are formulae determining an action which is necessary according to the principle of a will good in some respects. If now the action is good only as a means to something else, then the imperative is hypothetical; if it is conceived as good in itself and consequently as being necessarily the principle of a will which of itself conforms to reason, then it is categorical.
Thus the imperative declares what action possible by me would be good and presents the practical rule in relation to a will which does not forthwith perform an action simply because it is good, whether because the subject does not always know that it is good, or because, even if it know this, yet its maxims might be opposed to the objective principles of practical reason.
Accordingly the hypothetical imperative only says that the action is good for some purpose, possible or actual. In the first case it is a problematical, in the second an assertorial practical principle. The categorical imperative which declares an action to be objectively necessary in itself without reference to any purpose, i.e., without any other end, is valid as an apodeictic (practical) principle.
Whatever is possible only by the power of some rational being may also be conceived as a possible purpose of some will; and therefore the principles of action as regards the means necessary to attain some possible purpose are in fact infinitely numerous. All sciences have a practical part, consisting of problems expressing that some end is