Kantian ethics

1. Kant’s ethics

Kant’s main writing on ethics and politics can be found in Grundlegung zur Metaphysik der Sitten (Groundwork of the Metaphysics of Morals) (1785), Kritik der practischen Vernunft (Critique of Practical Reason) (1788), Die Metaphysik der Sitten (The Metaphysics of Morals) (1797) and numerous sections of other works and free-standing essays. Throughout these writings he insists that we cannot derive ethical conclusions from metaphysical or theological knowledge of the good (which we lack) or from a claim that human happiness is the sole good (which we cannot establish). We lack the basis for a teleological or consequentialist account of ethical reasoning, which therefore cannot be simply a matter of means-ends reasoning towards some fixed and knowable good (see Consequentialism; Teleological ethics).

Yet if reasoning about action, that is practical reasoning, is not means-end reasoning, what can it be? Kant’s alternative account proposes simply that reasons for action must be reasons for all. He insists that we can have reasons for recommending only those principles of action which could be adopted by all concerned, whatever their particular desires, social identities, roles or relationships. Correspondingly, practical reasoning must reject any principles which cannot be principles for all concerned, which Kant characterizes as non-universalizable principles (see Universalism in ethics §5).

Kant gives this rather limited modal conception of practical reasoning some grand names. He calls it the ‘supreme principle of morality’ and the ‘categorical imperative’. He formulates this fundamental principle of ethics in various ways. The formulation most discussed in the philosophical literature runs ‘act only on that maxim [principle] through which you can at the same time will that it become a universal law’ ([1785] 1903: 421). The formulation that has had and still has the greatest cultural resonance requires us to treat others with impartial respect. It runs ‘treat humanity…never simply as a means, but always at the same time as an end’ ([1785] 1903: 429) (see Respect for persons §2). The equivalence of these two formulations of the categorical imperative is far from obvious. One way of glimpsing why Kant thought they were equivalent is to note that if we treat others as persons rather than as things then we must not destroy or impair their abilities to act, indeed must leave it open to them to act on the same principles that we act on; hence we must act on universalizable principles. On Kant’s view, one of the worst features of consequentialist ethics is that it not merely permits but requires that persons be used as mere means if this will produce good results.

Kant claims that the categorical imperative can be used to justify the underlying principles of human duties (see Duty §2). For example, we can show by a reductio ad absurdum argument that promising falsely is not universalizable. Suppose that everyone were to adopt the principle of promising falsely: since there would then be much false promising, trust would be destroyed and many would find that they could not get their false promises accepted, contrary to the hypothesis of universal adoption of the principle of false promising. A maxim of promising falsely is not universalizable, so the categorical imperative requires us to reject it. Parallel arguments can be used to show that principles such as those of coercing or doing violence are not universalizable, and so that it is a duty to reject these principles.

Kant calls duties such as these perfect (namely, complete) duties. These are duties which can observed by each towards all others. He also provides arguments to establish the principles of certain imperfect (namely, incomplete) duties, such as those of helping others in need or developing one’s own talents. One way in which imperfect duties are unavoidably incomplete is that they cannot be observed towards all others: nobody can help all others, or develop all possible talents. Kant calls these imperfect duties ‘duties of virtue’ (see Virtues and vices §§2–3).

The derivation of principles of duty from his conception of practical reason is the core of Kant’s ethics, and provides the context for his discussion of many other themes. These include: the difference between internalizing principles and merely conforming to them in outward respects (‘acting out of duty’ versus ‘acting according to duty’); the place of happiness in a good life; the need for judgment in moving from principle to act (see Moral Judgment §2); the justification of state power; and the justification of a cosmopolitan account of justice. He also develops the connections between his distinctive conceptions of practical reason and of freedom and his equally distinctive view of religion, which he sees as a matter not of knowledge but of reasoned hope for a future in which morality can be fully realized. In some works Kant articulates reasoned hope in religious terms; in others he articulates it in political and historical terms as a hope for a better this-worldly human future (see Hope §3).