Principia Ethica

G. E. Moore

Moore is the book's author, narrator, and chief combatant — a Trinity College don who treats the entire history of moral philosophy as a crime scene of logical errors. He is disarmingly honest about his own work's defects, admitting in his preface that he could not stop correcting it without rewriting the whole book, yet he is ruthless toward the 'naturalistic fallacy' in others. His central obsession — that goodness is a simple, unanalyzable property, like yellow — drives the early chapters and sets the terms for every argument that follows.

J. S. Mill

Mill is the first major opponent Moore examines, and the one he treats with the most respect, calling his book an admirably clear and fair discussion of ethical principles. The tension is sharp: Moore admires Mill's method and honesty while arguing that his hedonistic conclusions rest on a confusion between 'desirable' and 'desired.' Mill's presence in the early chapters establishes the pattern for the whole book — careful exposition, then surgical refutation — and makes him the benchmark against which Moore measures every subsequent error.

Herbert Spencer

Spencer represents the ambitious Victorian attempt to ground morality in evolutionary science, a project Moore finds both influential and fundamentally confused. Where Spencer sees progress from natural facts to ethical conclusions, Moore sees a category mistake — the assumption that 'good' can be defined by any natural property, whether pleasure, evolution, or desire. Spencer matters to the book's middle arc because his theory forces Moore to articulate, with maximum precision, why the naturalistic fallacy is not a minor slip but the central error of modern ethics.

Henry Sidgwick

Sidgwick is Moore's most intimate intellectual interlocutor, cited in footnotes and argued with in the main text, and the one whose terminology Moore borrows even while rejecting the label 'Intuitionist.' Moore credits Sidgwick with recognizing that some ethical propositions are incapable of proof, but insists Sidgwick never grasped the full importance of distinguishing those from propositions about right action. This half-agreement, half-correction makes Sidgwick the book's most productive foil — a thinker close enough to Moore's position to sharpen it, and far enough to require the sharpening.

Jeremy Bentham

Bentham stands at the head of the hedonistic lineage Moore examines, the source of the idea that pleasure alone is good and pain alone evil. Moore does not engage Bentham as extensively as Mill, but Bentham's shadow falls across the entire hedonism chapter — his calculus is the crude original that later utilitarians refined but never, in Moore's view, escaped. Bentham matters to the early arc because he represents the purest form of the error Moore is hunting: the assumption that because pleasure is good, 'good' must mean pleasure.

Immanuel Kant

Kant is the towering representative of metaphysical ethics, the tradition that tries to derive ethical truths from metaphysical ones — a move Moore considers as fallacious as deriving them from natural facts. Yet Moore's relationship to Kant is not simple dismissal: he explicitly models his project on Kant's 'Prolegomena,' writing a 'Prolegomena to any future Ethics that can possibly pretend to be scientific.' Kant matters to the middle chapters because his categorical imperative, with its implied heteronomy objection, forces Moore to clarify what he means by calling ethical propositions 'Intuitions' — and what he emphatically does not mean.