Summary
Preface
Kant divides philosophy into logic, physics and ethics, then distinguishes empirical inquiry from pure rational inquiry. Moral philosophy requires a pure part because a genuine moral law must bind necessarily and cannot rest upon facts about variable human nature.
A metaphysic of morals isolates the principles of a possible pure will. Experience remains useful for applying laws and cultivating judgement, but it cannot supply their ultimate authority. Kant announces a movement from common moral knowledge to philosophical principle and then from that principle to a critique of practical reason.
First Section: From common moral knowledge to philosophy
The only unqualified good is a good will. Intelligence, courage, wealth and happiness are conditionally good because they can magnify harmful purposes. Good will retains its worth independently of success; its value lies in willing according to a right principle.
Duty clarifies good will where inclination competes with reason. Kant distinguishes action contrary to duty, action merely conforming to duty and action done from duty. Only the last has moral worth in the strict sense, because its determining ground is respect for law.
An action’s moral value lies in its maxim rather than its intended effect. Since material aims depend upon desire, the unconditional law must concern the form of universal legislation. Kant reaches the principle: act only on a maxim that you can also will as a universal law.
Ordinary reason already uses something like this test, but philosophical examination is needed because inclination can corrupt judgement and invent exceptions. The transition to philosophy protects common moral understanding from rationalisation.
Second Section: From popular philosophy to a metaphysic of morals
Examples cannot prove that a perfectly dutiful action has ever occurred, because inner motives cannot be observed with certainty. Moral concepts must therefore be derived a priori rather than generalised from behaviour.
Imperatives express how objective laws of reason relate to imperfect wills. Hypothetical imperatives command the means to optional or generally desired ends. The categorical imperative commands independently of any further end and is the proper form of moral obligation.
The Formula of Universal Law asks an agent to act only on a maxim that can be willed as universal law. The natural-law formulation asks the agent to imagine the maxim operating with the regularity of nature.
Kant tests four maxims. Suicide from self-love contradicts a natural system in which the same impulse both advances and destroys life. A false promise undermines the practice of promising when universalised. Neglecting one’s talents is conceivable but cannot rationally be willed as a universal policy. Refusing all assistance similarly conflicts with ends for which one may need others’ help.
These examples generate perfect duties, which admit no exception for inclination, and imperfect duties, which require adopting ends while permitting discretion in their fulfilment. Duties can be directed towards oneself or others.
The Formula of Humanity rests upon rational nature as an end in itself: act so that you use humanity, in your own person and in every other, always at the same time as an end and never merely as a means. Deception and coercion fail because they prevent another rational agent from sharing in the choice of the end.
The Formula of Autonomy understands every rational will as making universal law. The Kingdom of Ends is an ideal community in which rational beings are simultaneously members subject to common laws and sovereign legislators of them.
Rational nature possesses dignity rather than price. Skill, effort and agreeable qualities may have market or affective value, but morality and the capacity for autonomous legislation have incomparable worth.
All formulations express the same fundamental law from different perspectives. Heteronomous theories fail when they derive obligation from happiness, perfection, moral feeling, divine command understood through reward, or any desired object. Such principles produce only conditional imperatives.
Third Section: From a metaphysic of morals to pure practical reason
Freedom is the property by which a will can act independently of alien determining causes. Its positive meaning is autonomy: a free will gives universal law to itself. A will without any law would not be rationally free but merely arbitrary.
Kant argues that every rational being must act under the idea of freedom. Deliberation presupposes that reason can regard itself as the author of its judgements rather than a passive link in a chain of impulses.
Human beings understand themselves from two standpoints. As members of the sensible world, their actions appear under natural causality. As intelligible beings exercising reason, they regard themselves as belonging to an order of freedom. This distinction is meant to dissolve the apparent contradiction between natural necessity and moral responsibility.
The moral “ought” expresses what a rational being would necessarily will if reason fully governed it. Because human beings are also affected by inclinations, the law appears as an imperative and duty rather than as spontaneous holy willing.
Kant rejects attempts to explain freedom as an object of experience. Freedom is a necessary practical presupposition, not a phenomenon that theoretical knowledge can observe. Equally, the intelligible world cannot be used to claim knowledge beyond the conditions of possible experience.
The inquiry reaches its boundary when it asks how pure reason can itself be practical or generate an interest in moral law. Kant can show why no empirical interest grounds unconditional duty, but cannot provide a further comprehensible mechanism without destroying the very independence from nature that freedom requires.