Peter Albert David Singer, AC (born 6 July 1946) is an Australian moral philosopher. He is the Ira W. DeCamp Professor of Bioethics at Princeton University, and a Laureate Professor at the Centre for Applied Philosophy and Public Ethics at the University of Melbourne. He specializes in applied ethics and approaches ethical issues from a secular, utilitarian perspective. He is known in particular for his book, Animal Liberation (1975), a canonical text in animal rights/liberation theory. For most of his career, he supported preference utilitarianism, but in his later years became a classical or hedonistic utilitarian, when co-authoring The Point of View of the Universe with Katarzyna de Lazari-Radek.
Published in 1975, Animal Liberation has been cited as a formative influence on leaders of the modern animal liberation movement. The central argument of the book is an expansion of the utilitarian idea that “the greatest good of the greatest number” is the only measure of good or ethical behaviour. Singer believes that there is no reason not to apply this principle to other animals, arguing that the boundary between human and “animal” is completely arbitrary. There are far more differences, for instance, between a great ape and an oyster, for example, than between a human and a great ape, and yet the former two are lumped together as “animals,” whereas we are considered “human” in a way that supposedly differentiates us from all other “animals.”
He popularized the term “speciesism”, which had been coined previously by English writer Richard D. Ryder to describe the practice of privileging humans over other animals. In Animal Liberation, Singer argues in favour of vegetarianism and against animal experimentation.