The Methods of Ethics

The central claim is that ethics has three competing 'methods'—egoism, intuitionism, and utilitarianism—each purporting to be a rational procedure for determining right action. Sidgwick rejects the assumption that any one method can be vindicated as exclusively rational. His examination of common-sense morality shows it is largely utilitarian in substance but inconsistent in its principles. Yet utilitarianism itself rests on an axiom (rational benevolence) that cannot be shown superior to the egoist's axiom of prudence. The book's conclusion is a 'dualism of practical reason': two self-evident principles that may conflict, leaving the rational agent without a single authoritative method.

The 'dualism of practical reason' is the book's signature concept: the thesis that prudence (egoism) and rational benevolence (utilitarianism) are both grounded in apparently self-evident intuitions, yet they can prescribe incompatible actions. This is not a psychological claim about motivation but a claim about the structure of practical justification. Contemporary metaethics and normative ethics use the dualism to frame debates about whether morality is rationally required. Alison Hills has argued that the dualism argument is broader than Sidgwick supposed, applying to any attempt to show that a moral theory is rationally required, not merely to the egoism-utilitarianism conflict.

Mill's essay is a polemical defense of the greatest happiness principle as the foundation of morality. Sidgwick's treatise is a systematic, skeptical inquiry that treats utilitarianism as one method among three and subjects it to the same scrutiny as its rivals. Where Mill attempts a 'proof' of utility from the fact that people desire happiness, Sidgwick seeks self-evident axioms underlying the utilitarian method and finds that a rival axiom supports egoism equally well. Sidgwick also rejects the empiricist and naturalist framework of earlier utilitarians, arguing that ethical judgments contain a 'fundamental notion' of 'ought' that cannot be reduced to natural facts.

The dualism has proven remarkably durable, though its interpretation remains contested. Sidgwick's reputation declined in the early twentieth century but revived significantly from the 1970s onward. Derek Parfit's Reasons and Persons (1984) engaged directly with Sidgwickian themes, and the book is now standard reading alongside Rawls and Parfit in Anglo-American moral philosophy. Critics have questioned whether Sidgwick's axioms are genuinely self-evident or whether the dualism is a genuine rational impasse rather than a failure of Sidgwick's own arguments. The text's careful, non-dogmatic method has been admired even by those who reject its conclusions.

Common-sense morality—the ordinary moral convictions most people hold—serves as a testing ground rather than a foundation. Sidgwick treats it as a 'method' (intuitionism) to be examined for consistency and completeness. He concludes that common-sense rules are largely sound in substance but vague and inconsistent at the margins, requiring utilitarian principles to define and correct them. Crucially, however, this does not vindicate utilitarianism as the sole rational method, because the egoist can accept the practical overlap while denying the utilitarian's ultimate principle. The examination of common sense thus leads not to a triumphant utilitarianism but to the dualism.

Sidgwick distinguishes 'dogmatic' or 'perceptional' intuitionism—the claim that particular actions or rules are immediately known to be right—from 'philosophical' intuitionism, which seeks self-evident abstract axioms underlying moral reasoning. He subjects the former to devastating criticism, showing that common-sense rules admit of exceptions and conflict. His own philosophical intuitionism identifies a small number of abstract principles, including the axioms of prudence and rational benevolence. This distinction allows Sidgwick to reject the complacent intuitionism of his predecessors while retaining intuition as the only possible foundation for any ethical method, including utilitarianism.