Aterm which originated in Immanuel Kant's ethics. It expresses the moral law as ultimately enacted by reason and demanding obedience from mere respect for reason. Kant in his ethics takes his point of departure from the concept of a good will: "Nothing can possibly be conceived in the world or out of it that can be called good without qualification except a good will." But that will alone is good which acts not only conformably to duty, but also from duty. And again the will acts from duty when it is determined merely by respect for the law, independently of inclination, and without regard to the agreeableness or the consequences of the action prescribed. Therefore the first fundamental principle of morality is: "Let the law be the sole ground or motive of thy will." Kant further finds that the law is capable of inspiring respect by reason of its universality and necessity, and hence lays down the following general formula of the moral law: "Act so that the maxim [determining motive of the will] may be capable of becoming a universal law for all rational beings." Necessity and universality, he declares, cannot be derived from experience, whose subject matter is always particular and contingent, but from the mind alone, from the cognitive forms innate in it. Hence the moral law originates in pure reason and is enunciated by a synthetical judgment a priori--a priori because it has its reason, not in experience, but in the mind itself; synthetical, because it is formed not by the analysis of a conception, but by an extension of it. Reason, dictating the moral law, determines man's actions. Yet it may do so in a twofold manner. It either controls conduct infallibly, its dictates being actually responded to without conflict or friction--and in this case there is no obligation necessary or conceivable, because the will is of itself so constituted as to be in harmony with the rational order--or it is resisted and disobeyed, or obeyed only reluctantly, owing to contrary impulses coming from sensibility. In this case determination by the law of reason has the nature of a command or imperative, not of a hypothetical imperative, which enjoins actions only as a means to an end and implies a merely conditional necessity but of a categorical imperative, which enjoins actions for their own sake and hence involves absolute necessity. While for God, Whose will is perfectly holy, the moral law cannot be obligatory, it is for man, who is subject to sensuous impulses, an imperative command. Accordingly, the categorical imperative is the moral law enacted by practical reason, obligatory for man, whose sensibility is discordant from the rational order, and demanding obedience from respect for its universality and necessity.
Kant essays to prove the existence of a categorical imperative a priori from the idea of the will of a rational being Will is conceived as a faculty determining itself to action according to certain laws. Now it is only an end that serves as an objective principle for the self-determination of the will, and only an end in itself that serves as a universal principle holding for all rational beings. But man, and indeed every rational being, is an end in himself, a person, and must in all actions, whether they regard self or others, be respected as such. Thus arises a supreme practical principle, objective and universal, derived not from experience, but from human nature itself; a principle from which, as the highest practical ground, all laws of the will are capable of being derived. This, then, is the categorical imperative, to be enunciated in the following terms: Act so as to use humanity, whether in your own person or in others, always as an end, and never merely as a means.
Hence Kant infers, first, that the will of every rational being, by commanding respect for humanity as an end in itself,lays down a universal law, and is therefore a law unto itself, autonomous, and subject to no external lawgiver; secondly, that morality consists in obedience to the law of our own reason, and immorality, on the contrary, in heteronomy, that is, in obedience to any, even Divine, authority distinct from our own reason, or in action from any other motive than respect for our reason as a law.
The merits of Kant's categorical imperative are said to consist in this: that it firmly establishes the reign of reason; elevates the dignity of man by subjecting in him sensibility to reason and making rational nature free, supreme, and independent; overcomes egoism by forbidding action from self-interest; and upholds morality by the highest authority. But the theist philosopher and the Christian theologian must needs take another view. Man is not an end in himself, but is essentially subordinate to God as his ultimate end and supreme good; nor is he autonomous, but is necessarily subject to God as his supreme Lord and lawgiver. Man, conceived as a law unto himself and an end in himself, is emancipated from God as his master and separated from Him as his supreme good; conceived, moreover, as autonomous and independent of any higher authority, he is deified. This is not building up true and lofty morality, but is its complete overthrow; for the basis of morality is God as the ultimate end, highest good, and supreme lawgiver. Kant utterly ignores the nature of both intellect and will. Human reason does not enact the moral law, but only voices and proclaims it as the enactment of a higher power above man, and it is not from the proclaiming voice that the law derives its binding force, but from the majesty above that intimates it to us through our conscience.
Nor do the universality and necessity of a law determine the will. What really attracts the will, and stirs it as a motive to action, is the goodness of the object presented by the intellect; for the rational appetite is by its nature an inclination to good. Hence it is that the desire of perfect happiness necessarily results from rational nature, and that the supreme good, clearly apprehended by the mind, cannot but be desired and embraced by the will. Hence, too, a law is not presented as obligatory, unless its observance is known to be necessarily connected with the attainment of the supreme good. It is, therefore, wrong to denounce the pursuit of happiness as immoral or repugnant to human nature. On the contrary, a paralysis of all human energy and utter despair would result from bidding man to act only from the motive of stern necessity inherent in law, or forbidding him ever to have his own good in view or to hope for blessedness.
The theory of the categorical imperative is, moreover, inconsistent. According to it the human will is the highest lawgiving authority, and yet subject to precepts enjoined on it; it is absolutely commanding what is objectively right, and at the same time reluctant to observe the right order. Again, the categorical imperative, as also the autonomy of reason and the freedom of the will, belongs to the intelligible world, and is, therefore, according to the "Critique of Pure Reason", absolutely unknowable and contradicted by all laws of experience; nevertheless in Kantian ethics it is characterized as commanding with unmistakable precision and demanding obedience with absolute authority. Such a contradiction between Kant's "Critique of Pure Reason" and his "Ethics", between theoretical and practical reason, induces in morals a necessity which resembles fatalism.
Kant sets forth the categorical imperative in his "Fundamental Principles of the Metaphysics of Morals" (1785) and his "Critique of Practical Reason" (1788).