The moral theory that actions, rules, and institutions should be evaluated solely by their consequences for aggregate well-being. Its classical formula — "the greatest happiness of the greatest number" — is usually traced to Francis Hutcheson, but Jeremy Bentham is the figure who made it a system, and John Stuart Mill the one who made it philosophically respectable.
Three great strengths explain utilitarianism's staying power. It is egalitarian: each person counts for one, no one for more than one. It is secular and empirical: no appeal to God, tradition, or natural rights is required. And it is reformist: any institution, however venerable, can be dragged before the bar of consequences. These traits made it the natural ethics of 19th-century British reform and, in its cost-benefit guise, the default moral language of modern policy analysis.
Its famous difficulties are equally persistent. It appears, at least in crude versions, to license monstrous trade-offs (hang one innocent to satisfy the mob; harvest one to save five). It struggles to take distinctions between persons seriously — a critique John Rawls sharpened in A Theory of Justice. And its apparently simple currency — "utility," or happiness, or preference-satisfaction — turns out to be philosophically treacherous. Modern utilitarians have responded with rule utilitarianism, preference utilitarianism, and more elaborate variants, but the basic tension between aggregation and individual rights is the argument that defines the tradition.