Peter Singer argues in plain academic prose, one step at a time, and the conclusions arrive without a raised voice.

His starting point comes from Jeremy Bentham: the capacity to suffer is what earns a being moral consideration. On that basis Singer holds that an animal's interest in avoiding pain belongs in the same reckoning as a human's, and that discounting it by species is a prejudice of the same shape as the ones we already reject. He took the word speciesism from Richard D. Ryder and gave it wide currency. He also sets the language of rights aside, for animals and for people alike, treating rights as scaffolding his argument does not need.

Alongside the philosophy, Singer describes what factory farms and research laboratories were doing to animals in 1975, then asks the reader to hold the practice against the ethics. The book became the founding philosophical statement of the animal liberation movement, and Singer returned to it decades later as Animal Liberation Now, extending the case to meat's effect on the climate and to the spread of new viruses.

The position belongs to Singer, and he states it in terms a reader can weigh or refuse. Suited to anyone who wants the argument at its source rather than at second hand, in the philosopher's own words.