The English philosopher and legal reformer Jeremy Bentham (1748–1832) wanted to ground morality not in tradition, intuition, or religious command but in a single measurable principle. His 1789 "Introduction to the Principles of Morals and Legislation" states it plainly: nature has placed humankind under the governance of two masters — pleasure and pain. The moral worth of an action is determined by the ratio of total pleasure to pain it ultimately produces. The principle is: the greatest happiness of the greatest number.

This "principle of utility" (utilitarianism) was a revolutionary simplification. It turned a moral question — what is right — into a calculation. Bentham took this seriously; he even proposed a "felicific calculus" weighing pleasures by dimensions such as intensity, duration, certainty, and nearness. The aim was to turn subjective moral judgement into an objective measure that works the same for everyone.

For Bentham this was no abstract theory but a tool of reform. The law of his day was, in his view, arbitrary, cruel, and irrational. Making the principle of utility a touchstone, he rethought criminal law, prisons, and poor laws. Because its criterion is the capacity to suffer, utilitarianism also widened its bounds: Bentham wrote even then that animals too suffer and must therefore be included in the moral reckoning — "The question is not, Can they reason? nor, Can they talk? but, Can they suffer?"

His pupil John Stuart Mill refined utilitarianism by attending to the quality of pleasure; the principle is the ancestor of a broad family of thought reaching from modern economics to public policy, from cost-benefit analysis to contemporary ethics. Two centuries later Peter Singer would carry Bentham's criterion of suffering to the centre of animal ethics. The strongest objection to utilitarianism is born here too: can the happiness of the majority justify crushing the right of a minority?