Book: Groundwork of the Metaphysics of Morals

Purpose and Method

Kant sets out to identify the supreme principle of morality and to ground it a priori, independent of experience. He distinguishes a pure moral philosophy from empirical anthropology: only a law derived from reason alone can be universally binding. The book proceeds analytically from common moral judgment to the concept of a good will and duty, then synthetically to the principle capable of legislating moral obligations.

The Good Will and Duty

The only unconditionally good thing is a good will, good not because of its effects but through its willing. Talents, temperaments, and fortunate circumstances can be used wrongly; their value depends on the will that guides them. Moral worth arises when an action is done from duty, not merely in accord with duty. A shopkeeper who gives fair prices to preserve his reputation acts in conformity with duty; only if he acts from respect for the law does his action have moral worth. Similarly, helping others from sympathy is praiseworthy, but it exhibits moral worth only when beneficence is chosen because it is a duty. Duty is the necessity of an action from respect for the law; this “respect” is a practical recognition of the law’s authority, not a feeling we choose.

Hypothetical and Categorical Imperatives

Reason commands through imperatives. Hypothetical imperatives bind conditionally: if one wills an end, one ought to will the means. Moral obligation, however, must be unconditional. The categorical imperative commands independently of desired ends; it expresses a law that holds for every rational being as such. Because experience cannot supply necessity and universality, the moral law must be known a priori by pure practical reason.

Formulations of the Moral Law

Kant states the categorical imperative in several equivalent formulations. The Formula of Universal Law: act only on that maxim through which you can at the same time will that it become a universal law. Testing a maxim by universalization reveals contradictions. A maxim of false promising yields a contradiction in conception, showing a perfect duty not to lie. A maxim of never helping others yields no contradiction in conception but a contradiction in will, grounding an imperfect duty of beneficence. The Formula of Humanity: act so that you treat humanity, whether in your own person or in that of another, always as an end and never merely as a means. Rational nature has an absolute worth; using others merely as instruments violates their status as self-legislators. The Formula of the Kingdom of Ends: act as a legislating member of a systematic community of rational beings in which each is both subject and sovereign under common laws.

Autonomy, Freedom, and the Kingdom of Ends

The moral law’s authority rests on autonomy: the will’s capacity to give itself the law. Heteronomous principles, grounding morality in happiness, perfection, divine command, or any empirical incentive, cannot yield unconditional obligation. To regard oneself as bound by the moral law is to view oneself as free, belonging to an intelligible order where reason legislates. Kant argues from the standpoint of practical reason: the fact of the moral law gives a sufficient ground to think of ourselves as free, even if speculative reason cannot prove freedom.

Scope and Legacy

The book does not deliver a full moral system; it lays the foundation by isolating the principle of morality and clarifying its source in reason. By locating moral worth in autonomy and universal law, Kant reframes duties as self-legislation rather than external command. The result is a rigorous account of obligation that honors the dignity of persons and sets the agenda for modern deontological ethics.