Peter Singer is an Australian philosopher whose work made applied ethics a serious field and whose conclusions have made him among the most argued-with living philosophers.

Animal Liberation

His 1975 book argues that the capacity to suffer, not intelligence or species membership, is what gives a being moral standing. If suffering counts, it counts wherever it occurs, and discounting it because the sufferer is not human is a prejudice he named speciesism by analogy with racism.

The argument is straightforwardly utilitarian and does not depend on sentiment about animals. It asks which differences are morally relevant and concludes that species is not one of them.

The drowning child

His 1972 essay on famine relief poses a case. You pass a shallow pond where a child is drowning. Saving them ruins your clothes. Obviously you should.

Then: if you can prevent something very bad without sacrificing anything of comparable moral importance, you ought to. Distance makes no moral difference, and neither does the fact that others could help and are not helping. The conclusion is that affluent people are obliged to give away far more than they do.

Most readers accept each premise and reject the conclusion, which is what makes the argument work as philosophy: it forces you to say which step fails.

The uncomfortable cases

Singer follows the same reasoning into infanticide, euthanasia and disability, where his conclusions have drawn sustained protest, including from disability rights advocates who argue his framework treats their lives as of lesser value. He has engaged the criticism and not substantially retreated.

Why he matters

He demonstrated that moral philosophy could address what people actually do without becoming less rigorous. The effective altruism movement descends from his arguments, as does a considerable part of contemporary animal ethics. See ethics.