Introduction to the Metaphysic of Morals, I.: of the relation of the faculties of the human mind to the moral laws.

THE appetitive faculty is the faculty of being by means of one’s ideas the cause of the objects of these ideas. The faculty which a being has of acting according to its ideas is Life. Firstly—Desire or aversion has always connected with it pleasure or displeasure, the susceptibility to which is called feeling. But the converse does not always hold; for a pleasure may exist which is not connected with any desire of the object, but with the mere idea which one frames to one’s self of an object, no matter whether its object exists or not. Secondly—The pleasure or displeasure in the object of the desire does not always precede the desire, and cannot always be regarded as its cause, but must sometimes be looked on as the effect thereof.

Now, the capability of having pleasure or displeasure in an idea is called feeling, because both contain what is merely subjective in relation to our idea , and have no relation to an object so as to contribute to the possible cognition of it (not even the cognition of our own state); whereas in other cases sensations, apart from the quality which belongs to them in consequence of the nature of the subject (ex. gr. red, sweet, etc.), may yet have relation to an object, and constitute part of our knowledge; but pleasure or displeasure (in the red or sweet) expresses absolutely nothing in the object, but simply a relation to the subject. Pleasure and displeasure cannot be more closely defined, for the reason just given. We can only specify what consequences they have in certain circumstances so as to make them cognizable in practice. The pleasure which is necessarily connected with the desire of the object whose idea affects feeling may be called practical pleasure, whether it is cause or effect of the desire. On the contrary, the pleasure which is not necessarily connected with the desire of the object, and which, therefore, is at bottom not a pleasure in the existence of the object of the idea, but clings to the idea only, may be called mere contemplative pleasure or passive satisfaction . The feeling of the latter kind of pleasure we call taste. Accordingly, in a practical philosophy we can treat this only episodically, not as a notion properly belonging to that philosophy. But as regards the practical pleasure, the determination of the appetitive faculty which is caused, and therefore necessarily preceded by this pleasure, is called appetite in the strict sense, and habitual appetite is called inclination. The connexion of pleasure with the appetitive faculty, in so far as this connexion is judged by the understanding to hold good by a general rule (though only for the subject), is called interest, and hence in this case the practical pleasure is an interest of inclination. On the other hand, if the pleasure can only follow an antecedent determination of the appetitive faculty, it is an intellectual pleasure, and the interest in the object must be called an interest of reason. For if the interest were one of sense, and not merely founded on pure principles of reason, sensation must be joined with pleasure, and thus be able to determine the appetitive faculty. Although where a merely pure interest of reason must be assumed, no interest of inclination can be substituted for it, yet in order to accommodate ourselves to common speech, we may admit an inclination even to that which can only be the object of an intellectual pleasure—that is to say, a habitual desire from a pure interest of reason. This, however, would not be the cause but the effect of the latter interest, and we might call it the sense-free inclination (propensio intellectualis). Further, concupiscence is to be distinguished from the desire itself as being the stimulus to its determination. It is always a sensible state of mind, but one which has not yet arrived at an act of the appetitive faculty.

The appetitive faculty which depends on concepts, in so far as the ground of its determination to action is found in itself , not in the object, is called a faculty of doing or forbearing as we please. In so far as it is combined with the consciousness of the power of its action to produce its object, it is called “elective will” [Willkühr = arbitrium]; if not so combined, its act is called a wish. The appetitive faculty, whose inner determining principle, and, consequently, even its “good pleasure” (Belieben), is found in the reason of the subject, is called the Rational Will [Wille]. Accordingly the Rational Will is the appetitive faculty, not (like the elective will) in relation to the action, but rather in relation to what determines the elective will [Willkühr] to the action; and it has properly itself no determining ground; but in so far as it can determine the elective will, it is practical reason itself.

Under the will may be included the elective will [Willkühr], and even mere wish, inasmuch as reason can determine the appetitive faculty; and the elective will, which can be determined by pure reason, is called free elective will. That which is determinable only by inclination would be animal elective will (arbitrium brutum). Human elective will, on the contrary, is one which is affected but not determined by impulses. It is accordingly in itself (apart from acquired practice of reason) not pure; but it can be determined to actions by the pure will. Freedom of the elective will is just that independence of its determination on sensible impulses: this is the negative concept of it. The positive is: the power of pure reason to be of itself practical. Now this is possible only by the subordination of the maxim of every action to the condition of fitness for universal law. For being pure reason it is directed to the elective will, irrespective of the object of this will. Now it is the faculty of principles (in this case practical principles, so that it is a legislative faculty) ; and since it is not provided with the matter of the law, there is nothing which it can make the supreme law and determining ground of the elective will except the form, consisting in the fitness of the maxim of the elective will to be a universal law. And since from subjective causes the maxims of men do not of themselves coincide with those objective maxims, it can only prescribe this law as an imperative of command or prohibition.

These laws of freedom are called, in contradistinction to physical laws, moral laws. In so far as they are directed to mere external actions and their lawfulness, they are called judicial; but when they demand that these laws themselves shall be the determining ground of the actions, they are ethical, and in this case we say—the agreement with the former constitutes the legality, agreement with the latter the morality of the action. The freedom to which the former laws relate can only be freedom in its external exercise; but the freedom to which the latter refer is freedom both in the internal and external exercise of the elective will in as far, namely, as this elective will is determined by laws of reason. Similarly, in theoretic philosophy we say, that only the objects of the outer senses are in space, while the objects both of the external and of the internal sense are in time; because the ideas of both are still ideas, and for this reason all belong to the inner sense. Just so, whether we regard freedom in the external or the internal exercise of the elective will, in either case its laws, being pure practical laws of reason governing free elective will generally, must be also its internal grounds of determination; although they need not always be considered in this point of view.