Singer (like Socrates) takes philosophy and puts it where it belongs--in the market place. In lucid, non-technical prose he tackles disputed moral questions--most notably abortion, euthanasia, civil disobedience, equality, animal rights, and the obligations of the haves to the have-nots--with a compelling blend of intellectual rigor and personal commitment. (An earlier, more limited example: Animal Liberation, 1975.) Singer calls himself a consequentialist, i.e., a utilitarian who measures acts against the norm of "what, on balance, furthers the interests of those affected" rather than with any simple calculus of pleasure and pain. He follows this guideline wherever it leads him--and sometimes winds up out on some pretty controversial limbs. He maintains, for instance, that some animals (chimpanzees, among others) are persons, because they are self-conscious, communicate, and have a notion of the future. Killing an adult, nonhuman primate, then, would be worse than killing a human baby, which is not a person in the strict sense. Singer is not promoting infanticide, but challenging this and other forms of "speciesism," a blind moral prejudice in favor of humanity. In another chapter he proposes with cool but passionate eloquence that withholding help from starving people (e.g., by spending money on luxuries instead of sending it to CARE) is "the moral equivalent of murder." Here and elsewhere Singer stops short of laying down any absolutes, but takes a bold stance that provokes the reader to respond, one way or another. Anti-abortionists will argue--with reason--that he does scant justice to the fetus' status as a potential human being. And ecologists will protest the narrowness of his view that only sentient beings are entitled to ethical consideration (so it's wrong to eat a hamburger, but all right to destroy a redwood forest?). Finally, professional philosophers will complain about the relative flimsiness of Singer's concluding chapter, "Why Act Morally?" on which, logically speaking, his whole case rests. But, whatever the objections, this is a superb performance, rich in substance and immaculately written: critical thinking at its creative best.