Utilitarianism is the moral philosophy of consequences: an act is right as it tends to produce the greatest happiness for the greatest number, and every being's suffering counts exactly as much as any other's.
Jeremy Bentham stated the principle of utility in 1789 and built a reformer's career on it — prisons, poor laws, suffrage, animal welfare — and John Stuart Mill gave it its classic defense in 1863. Dormant as a school for a century, it returned with Peter Singer's work on poverty and animals to become the working ethic of effective altruism and a standing challenge to every morality of rules, intentions, and special obligations.
Ultimate Reality
'Nature has placed mankind under the governance of two sovereign masters, pain and pleasure': Bentham's opening sentence is the school's metaphysics in miniature. Value is not found in heaven, nature's purposes, or the moral law, but in sentient experience itself — the only place, the school argues, where anything has ever actually mattered to anyone.
The Human Condition
The human problem is partiality armed with principles: we privilege our own, our tribe's, and our species' suffering, and we dress the privilege as duty, tradition, or rights. Moral progress, in the school's historiography, is the circle of counted beings widening — Bentham's footnote on animals ('the question is not, Can they reason? but, Can they suffer?') is its founding expansion.
Knowledge and Truth
Moral knowledge is empirical and aggregative: find out what actually happens, to how many, how intensely, and for how long. The felicific calculus Bentham sketched is now the cost-effectiveness analysis of global health. Truth in ethics is therefore revisable by data in a way rule-based systems resist — the school treats that resistance as the symptom it treats.
Right and Wrong
Right is maximizing expected well-being impartially; wrong is everything else, however venerable. Act utilitarianism judges each deed by its consequences, rule utilitarianism by the consequences of its general adoption, and two-level versions let intuition govern daily life while the calculus governs reflection. Special obligations — to family, to compatriots — survive only as useful approximations, never as trumps.
Human Destiny
The school's horizon is the reduction of suffering across all sentient life and all future time — a destiny that makes the far future morally enormous, since the number of possible future beings dwarfs the present. Longtermism is this arithmetic taken seriously, and it converts destiny from a promise into a responsibility with no ceiling.
The Conversation
Utilitarianism asks every other ethic to justify the suffering its rules permit: the patient not saved so a principle could be kept, the animal whose pain counted for nothing. Its critics answer with the separateness of persons — that a sum across lives is nobody's good — and with the integrity objection: a morality that can require anything has already, somewhere, required too much.