Peter Singer was already one of the most influential applied ethicists before the publication of Practical Ethics. He made his mark through his work on civil disobedience, famine relief, and animal liberation. In Practical Ethics, Singer expands on some of his earlier arguments and extends his analyses to other contemporary moral problems. The book is written in a clear, unadorned style that makes its arguments accessible to nonspecialists without sacrificing philosophical subtlety.

Singer’s overall aim is to show how a broadly utilitarian theory successfully treats such problems as moral equality, animal rights, abortion, euthanasia, obligations of the affluent to the impoverished, and the justification of means to ends.

Singer begins with a chapter on the nature of ethics. He counters common misconceptions, pointing out that ethics is not a set of prohibitions primarily concerned with sex, it is not merely a theoretical model that cannot be applied in everyday life, it is not dependent on a religious context, and it is not relative. Instead, Singer understands the point of ethical judgments to be the guiding of human practices. Moreover, the objectivity in ethics involves the kinds of reasons and justifications that are offered within the moral enterprise. Ethical reasons are universal: They go beyond one’s own likes and dislikes and rise to the standpoint of the impartial spectator or ideal observer, which elevates them from the merely relative or subjective.

The moral point of view requires that one’s own interests cannot, simply because they are one’s interests, count more than the interests of anyone else; thus, one must give equal weight to the interests of all. Singer insists that the universal aspect of ethics therefore provides a persuasive, although not necessarily conclusive, reason for taking a broadly utilitarian position. In fact, utilitarianism, the view that an action is morally sound if and only if no other action available will foreseeably produce better overall consequences to those affected, is the minimal moral position reached by universalizing moral decision making. To go beyond utilitarianism, says Singer, people must be provided additional good reasons.

The moral point of view thus requires the principle of equal consideration of interests: One must give equal weight in moral deliberations to the like interests of all those affected by one’s actions. An interest is an interest, whoever’s interest it may be. The principle of equal consideration does not depend on a belief in factual equality, the belief that all people or all interest-bearers are actually equal in relevant physical and mental respects. Instead, it depends on the conviction that the most important interests, such as the interest in avoiding pain, in developing one’s abilities, in satisfying basic needs, in enjoying personal relationships, and in being free to pursue projects, are not affected by factual inequalities.

The rest of the book works out the implications of the principle of equal consideration of interests from a utilitarian standpoint. In general, Singer argues that people’s moral calculations and practices should change: People should accord more weight to the interests of animals than they currently do and less weight to members of their own species, such as fetuses, newborns, the severely retarded, and the senile, whose possession of interests is problematic. Consequently, some nonhuman lives, judged from the standpoint of richness of interests, are of higher quality than some human lives. In certain cases, abortion, euthanasia, and the killing of defective infants are justified, and some types of treatment of animals are morally prohibited. Singer adds that it is speciesism to give greater weight to the interests of members of one’s own species when there is a clash between their interests and the interests of those of other species.

Singer applies the principle of equal consideration from a combination of classical and preference utilitarian theories. Classical utilitarianism is formulated around maximizing pleasure and minimizing pain, whereas preference utilitarianism is formulated around maximizing the fulfillment of desires and preferences. In his discussion of racial, sexual, and species equality, Singer emphasizes a version of classical utilitarianism. In his discussion of killing people and animals, he highlights preference utilitarianism in the case of persons, while referring to classical utilitarianism in the case of nonpersons. A person, for Singer, is a rational, self-conscious creature whose self-consciousness involves seeing oneself with a future and having desires related to that future, including the desire to continue living.

Practical Ethics contains an extensive discussion of the wrongness of killing. Preference utilitarianism provides a direct reason for not killing persons: Killing frustrates the person’s future-related desire to continue living. Classical utilitarianism provides only an argument from side effects, at least when the killing is instantaneous and painless, which is merely an indirect reason for not killing. The argument is that painlessly killing some people increases the unhappiness of surviving people who will worry that they might be killed in the future. Thus, there are two utilitarian reasons for holding that the killing of a person is more seriously wrong than the killing of a nonperson: The classical utilitarian concern with side effects and the preference utilitarian concern with the frustration of the victim’s desires and plans for the future. Singer also entertains, although he does not explicitly endorse, two nonutilitarian reasons: the argument that the capacity to have desires about one’s future is a necessary condition of a right to life, and respect for autonomy.

In the case of killing animals for food, clothing, medical experimentation, and sport, people must first determine whether the animals in question are persons. Singer offers chimpanzees, gorillas, monkeys, whales, dolphins, seals, bears, pigs, dogs, and cats as candidates for personhood. He rejects fish, reptiles, chickens, and other birds. If an animal is a person, then, at least, the strong preference utilitarian objection to killing holds. If it is not a person, then none of the utilitarian reasons against killing hold when the killing is painless and no other animals are adversely affected. Killing an animal that is not a person would still reduce the amount of pleasure in the world because it eliminates one sentient being, but this is a relatively weak reason not to kill. Singer, acknowledging this, departs from his earlier work on animal liberation by accepting a replaceability argument and admitting that “in some circumstances—when animals lead pleasant lives, are killed painlessly, their deaths do not cause suffering to other animals, and the killing of one animal makes possible its replacement by another who would not otherwise have lived—the killing of a nonself-conscious animal [a nonperson] may not be wrong.”

Regarding abortion, Singer rejects the view that a fetus embodies moral significance because it is a potential person. He concludes that the life of a fetus or even a newborn has no greater value than the life of a nonhuman animal at a similar level of rationality, self-consciousness, awareness, and capacity to feel. The grounds for not killing persons therefore do not apply to fetuses or newborns. Restrictions on infanticide should issue only from the argument from side effects: the adverse effects of infanticide on others, particularly the parents of the victim. In cases of abortion where the people most affected, such as the prospective mother, want the abortion, the argument from side effects typically will not create moral prohibitions.

Singer also argues that voluntary euthanasia, the killing of a person with that person’s consent, is often morally permissible. When a person suffering from a painful and incurable disease wishes to die, neither the usual utilitarian nor nonutilitarian objections to killing apply. Under certain circumstances, Singer also endorses nonvoluntary euthanasia: when those killed lack the capacity to understand the choice between their continued existence or nonexistence, when that capacity will not be recovered or gained, when the foreseeable quality of life of the subject will be extremely poor, and when the argument from side effects creates no moral prohibition.

Singer’s most passionate arguments are directed at the reallocation of wealth from the developed nations to the poor of the undeveloped nations. He rejects the view that there is a morally relevant distinction between acts such as killing and omissions such as letting others die who require aid to survive. Singer argues that the relatively affluent have an obligation to help those in absolute poverty that is just as strong as their obligation to rescue a drowning child from a pond when they can help without sacrificing anything of comparable moral significance. He provides numerous facts and examples that highlight the consequences of people’s typical neglect of the impoverished of the world. Singer suggests a minimum ethical standard: Those earning average or above average incomes in affluent societies, unless they have an unusually large number of dependents or other special needs, ought to give one tenth of their income to reducing absolute poverty.

When addressing the issue of why people should act morally, Singer claims that the notion of ethics has become misleading to the extent that moral worth is attributed only to actions taken because they are right, without any ulterior motive. He suggests that to act morally probably will make people happy, because fulfillment can be gained from the outward-looking, impartial way of life instead of from a direct search for happiness. Happiness can be an internal reward for moral achievements. Although those who do not follow the process are not necessarily irrational, self-awareness and reflection on the nature and point of human existence may lead people toward concerns broader than narrow self-interest.

Practical Ethics has been widely used in philosophy courses in North America, the United Kingdom, and Australia, and it has been translated into German, Italian, Spanish, and Swedish. The book solidified Singer’s standing as the most influential contemporary utilitarian philosopher. Many organizations concerned with animal rights, famine relief, and euthanasia regard Singer as their ideological mentor.

Critics, however, charge that Singer fails to demonstrate why thinking ethically and impartially about everyone’s interests requires people to add up these interests and weigh them overall in a utilitarian calculus. Nonutilitarian methods permit people to evaluate the interests of everyone impartially without weighing them overall. More fundamentally, Singer never persuasively explains why morality requires people to consider all interests equally without regard for whose interests they are. That in mind, Practical Ethics may tacitly adopt an inadequate concept of the value of personal relations. Universal benevolence and sympathy—treating all others as equal objects of concern, respect, and intimacy—are insufficient. A world of no friendship and of no neighborly or family affection is one that few would choose to inhabit even on the condition that it yielded slight gains in overall happiness. If people’s natural desires toward partiality do not translate into behavioral partiality, they become deeply conflicted. Can people have deeply felt bonds of love but still remain impartial when meting out resources and service goods? Does Singer’s 10 percent solution adequately lessen the conflict?

Moreover, Singer may not have adequately dealt with a fundamental objection to utilitarianism: that it can justify sacrificing the paramount interests of a few for the minor interests of many others. Singer claims that the principle of equal consideration of interests does not permit such a result, but his examples fail to establish that claim. Finally, Singer’s refusal to be swayed by results that sometimes seem radically at odds with considered judgments calls into question what he takes to be the criteria of soundness for ethical theories. Appeals to self-evidence ring hollow to those not already committed to utilitarianism.

In 1993, a second edition of Practical Ethics was published. All the chapters of the first edition were revised. One new chapter applies the arguments on equality and poverty to the problem of international refugees. Another applies Singer’s blend of classical and preference utilitarianism to environmental ethics. The appendix outlines Singer’s experiences in Germany and Austria, where his views on euthanasia met widespread criticism, especially from those acutely sensitive to the horrifying human experiments of the Nazi regime and from the disabled. Many parts of the book are updated to take into account certain technical developments since the first edition, such as in vitro fertilization, embryo experimentation, assisted suicides, and the emergence of environmental activism.