His most comprehensive work,
Practical Ethics (1979), analyses in detail why and how beings' interests should be weighed. His principle of equal consideration of interests does not dictate equal treatment of all those with interests, since different interests warrant different treatment. All have an interest in avoiding pain, for instance, but relatively few have an interest in cultivating their abilities. Not only does his principle justify different treatment for different interests, but it allows different treatment for the same interest when diminishing marginal utility is a factor, favoring, for instance, a starving person's interest in food over the same interest of someone who is only slightly hungry.
Among the more important human interests are those in avoiding pain, in developing one's abilities, in satisfying basic needs for food and shelter, in enjoying warm personal relationships, in being free to pursue one's projects without interference, "and many others". The fundamental interest that entitles a being to equal consideration is the capacity for "suffering and/or enjoyment or happiness". He holds that a being's interests should always be weighed according to that being's concrete properties. He favors a 'journey' model of life, which measures the wrongness of taking a life by the degree to which doing so frustrates a life journey's goals. The journey model is tolerant of some frustrated desire and explains why persons who have embarked on their journeys are not replaceable. Only a personal interest in continuing to live brings the journey model into play. This model also explains the priority that Singer attaches to
interests over trivial desires and pleasures.
He requires the idea of an impartial standpoint from which to compare interests. He has wavered about whether the precise aim is the total amount of satisfied interests or the most satisfied interests among those beings who already exist prior to the decision one is making. The second edition of
Practical Ethics disavows the first edition's suggestion that the total and prior-existence views should be combined. The second edition asserts that preference-satisfaction utilitarianism, incorporating the 'journey' model, applies without invoking the first edition's suggestion about the total view. But the details are fuzzy and Singer admits that he is "not entirely satisfied" with his treatment.
Ethical conduct is justifiable by reasons that go beyond prudence to "something bigger than the individual," addressing a larger audience. Singer thinks this going-beyond identifies moral reasons as "somehow universal", specifically in the injunction to 'love thy neighbor as thyself', interpreted by him as demanding that one give the same weight to the interests of others as one gives to one's own interests. This universalising step, which Singer traces from Kant to Hare, is crucial and sets him apart from those moral theorists from Hobbes to David Gauthier, who tie reasons to prudence. Universalisation leads directly to utilitarianism, Singer argues, on the strength of the thought that one's own interests cannot count for more than the interests of others. Taking these into account, one must weigh them up and adopt the course of action that is most likely to maximise the interests of those affected; utilitarianism has been arrived at. Singer's universalising step applies to interests without reference to who has them, whereas a Kantian's applies to the judgments of rational agents (in Kant's kingdom of ends, or Rawls's Original Position, etc.). Singer regards Kantian universalization as unjust to animals. As for the Hobbesians, Singer attempts a response in the final chapter of
Practical Ethics, arguing that self-interested reasons support adoption of the moral point of view, such as 'the paradox of hedonism', which counsels that happiness is best found by not looking for it, and the need most people feel to relate to something larger than their own concerns.
Practical Ethics includes a chapter arguing for the redistribution of wealth to ameliorate absolute poverty (Chapter 8, "Rich and Poor"), and another making a case for resettlement of refugees on a large scale in industrialised countries (Chapter 9, "Insiders and Outsiders"). Although the natural, non-sentient environment has no intrinsic value for a utilitarian like Singer, environmental degradation is a profound threat to sentient life, and for this reason environmentalists are right to speak of wilderness as a 'world heritage'.
Abortion, euthanasia and infanticide
Consistent with his general ethical theory, Singer holds that the right to life is intrinsically tied to a being's capacity to hold preferences, which in turn is intrinsically tied to a being's capacity to feel pain and pleasure. In his view, the central argument against abortion is equivalent to the following logical syllogism:
First premise: It is wrong to take innocent human life.
Second premise: From conception onwards, the embryo or fetus is innocent, human and alive.
Conclusion: It is wrong to take the life of the embryo or fetus.
In his book
Rethinking Life and Death, as well as in
Practical Ethics, Singer asserts that, if we take the premises at face value, the argument is deductively valid. Singer comments that those who do not generally think abortion is wrong attack the second premise, suggesting that the fetus becomes a "human" or "alive" at some point after conception; however, Singer argues that human development is a gradual process, that it is nearly impossible to mark a particular moment in time as
the moment at which human life begins.
Singer's argument for abortion differs from many other proponents of abortion; rather than attacking the second premise of the anti-abortion argument, Singer attacks the first premise, denying that it is wrong to take innocent human life:
[The argument that a fetus is not alive] is a resort to a convenient fiction that turns an evidently living being into one that legally is not alive. Instead of accepting such fictions, we should recognise that the fact that a being is human, and alive, does not in itself tell us whether it is wrong to take that being's life.
Singer states that arguments for or against abortion should be based on utilitarian calculation which weighs the preferences of a mother against the preferences of the fetus. In his view a preference is anything sought to be obtained or avoided; all forms of benefit or harm caused to a being correspond directly with the satisfaction or frustration of one or more of its preferences. Since a capacity to experience the sensations of suffering or satisfaction is a prerequisite to having any preferences at all, and a fetus, at least up to around eighteen weeks, says Singer, has no capacity to suffer or feel satisfaction, it is not possible for such a fetus to hold any preferences at all. In a utilitarian calculation, there is nothing to weigh against a mother's preferences to have an abortion; therefore, abortion is morally permissible.
Similar to his argument for abortion, Singer argues that newborns similarly lack the essential characteristics of personhood..."rationality, autonomy, and self-consciousness"...and therefore "killing a newborn baby is never equivalent to killing a person, that is, a being who wants to go on living."
Singer classifies euthanasia as voluntary, involuntary, or non-voluntary. Voluntary euthanasia is that with the consent of the subject.
Singer's book
Rethinking Life and Death: The Collapse of Our Traditional Ethics offers further examination of the ethical dilemmas concerning the advances of medicine. He covers the value of human life and quality of life ethics in addition to abortion and other controversial ethical questions.
Singer has experienced the complexities of some of these questions in his own life. His mother had Alzheimer's disease. He said, "I think this has made me see how the issues of someone with these kinds of problems are really very difficult". In an interview with Ronald Bailey, published in December 2000, he explained that his sister shares the responsibility of making decisions about his mother. He did say that, if he were solely responsible, his mother might not continue to live.
World poverty
In "Famine, Affluence, and Morality", one of Singer's best-known philosophical essays, he argues that the injustice of some people living in abundance while others starve is morally indefensible. Singer proposes that anyone able to help the poor should donate part of their income to aid poverty relief and similar efforts. Singer reasons that, when one is already living comfortably, a further purchase to increase comfort will lack the same moral importance as saving another person's life. Singer himself reports that he donates 25 percent of his salary to Oxfam and UNICEF. In "Rich and Poor", the version of the aforementioned article that appears in the second edition of
Practical Ethics, his main argument is presented as follows:
If we can prevent something bad without sacrificing anything of comparable significance, we ought to do it; absolute poverty is bad; there is some poverty we can prevent without sacrificing anything of comparable moral significance; therefore we ought to prevent some absolute poverty.
Singer's most recent book,
The Life You Can Save, makes the argument that it is a clear-cut moral imperative for citizens of developed countries to give more to charitable causes that help the poor. While Singer acknowledges that there are problems with ensuring that money goes where it is most needed and that it is used effectively, he does not think that these practical difficulties undermine his original conclusion (that people should make a much greater effort to reduce poverty).
Other views
Zoophilia
In a 2001 review of Midas Dekker's
Dearest Pet: On Bestiality, Singer argues that sexual activities between humans and animals that result in harm to the animal should remain illegal, but that "sex with animals does not always involve cruelty" and that "mutually satisfying activities" of a sexual nature may sometimes occur between humans and animals, and that writer Otto Soyka would condone such activities. The position was countered by fellow philosopher Tom Regan, who writes that the same argument could be used to justify having sex with children. Regan writes that Singer's position is a consequence of his adapting a utilitarian, or consequentialist, approach to animal rights, rather than a strictly rights-based one, and argues that the rights-based position distances itself from non-consensual sex. The Humane Society of the United States takes the position that all sexual molestation of animals by humans is abusive, whether it involves physical injury or not.
Commenting on Singer's article "Heavy Petting," in which he argues that zoosexual activity need not be abusive, and that relationships could form which were mutually enjoyed, Ingrid Newkirk, president of the animal rights group PETA, argued that, "If a girl gets sexual pleasure from riding a horse, does the horse suffer? If not, who cares? If you French kiss your dog and he or she thinks it's great, is it wrong? We believe all exploitation and abuse is wrong. If it isn't exploitation and abuse, [then] it may not be wrong." A few years later, Newkirk clarified in a letter to the
Canada Free Press that she was strongly opposed to any exploitation of, and all sexual activity with, animals.
Singer believes that although sex between species is not normal or natural, it does not constitute a transgression of our status as human beings, because human beings are animals or, more specifically, "we are great apes".
Evolutionary biology and leftist politics
In
A Darwinian Left, Singer outlines a plan for the political left to adapt to the lessons of evolutionary biology. He says that evolutionary psychology suggests that humans naturally tend to be self-interested. He further argues that the evidence that selfish tendencies are natural must not be taken as evidence that selfishness is right. He concludes that game theory (the mathematical study of strategy) and experiments in psychology offer hope that self-interested people will make short-term sacrifices for the good of others, if society provides the right conditions. Essentially Singer claims that although humans possess selfish, competitive tendencies naturally, they have a substantial capacity for cooperation that has also been selected for during human evolution. Singer's writing in
Greater Good magazine, published by the Greater Good Science Center of the University of California, Berkeley, includes the interpretation of scientific research into the roots of compassion, altruism, and peaceful human relationships.
Nonetheless, he is not anti-capitalist. In an interview with New Left Project in 2010, he says the following:
Capitalism is very far from a perfect system, but so far we have yet to find anything that clearly does a better job of meeting human needs than a regulated capitalist economy coupled with a welfare and health care system that meets the basic needs of those who do not thrive in the capitalist economy.
He then adds that "If we ever do find a better system, I'll be happy to call myself an anti-capitalist."
Vegetarianism and ethics of food consumption
In an article for the online publication chinadialogue Singer called Western-style meat production cruel, unhealthy and damaging to the ecosystem. He rejected the idea that the method was necessary to meet the population's increasing demand, explaining that animals in factory farms have to eat food grown explicitly for them, and they burn up most of the food's energy just to breathe and keep their bodies warm.
Singer calls himself a vegetarian and a "flexible vegan". In his May 2006 interview in
Mother Jones, he states:
I don't eat meat. I've been a vegetarian since 1971. I've gradually become increasingly vegan. I am largely vegan but I'm a flexible vegan. I don't go to the supermarket and buy non-vegan stuff for myself. But when I'm traveling or going to other people's places I will be quite happy to eat vegetarian rather than vegan.
In addition to his addressing issues concerning the consumption of animal products, Singer's "Can You Do Good by Eating Well?" in
Greater Good examines the ethics of eating locally grown food.
Personism
Although he has expressed admiration for many of the values promoted by secular humanism, Singer believes it to be incomplete and promotes a sort of utilitarian personism instead.
Criticism of Singer
Singer's positions have been criticised by groups concerned with what they see as his attack upon human dignity, such as advocates for disabled people and right-to-life supporters. Singer has replied that many people judge him based on secondhand summaries and short quotations taken out of context, not his books or articles.
Some claim that Singer's utilitarian ideas lead to eugenics. American publisher Steve Forbes ceased his donations to Princeton University in 1999 because of Singer's appointment to a prestigious professorship. Steve Forbes Declines Princeton Financial Backing Due to Singer Hiring Nazi-hunter Simon Wiesenthal wrote to organisers of a Swedish book fair to which Singer was invited that "A professor of morals ... who justifies the right to kill handicapped newborns ... is in my opinion unacceptable for representation at your level." Marc Maurer, President of the National Federation of the Blind, criticised Singer's appointment to the Princeton Faculty in a banquet speech at the organisation's national convention in July 2001, claiming that Singer's support for euthanizing disabled babies could lead to disabled older children and adults being valued less as well. Independence and the Necessity for Diplomacy
In 1989, when Peter Singer attempted to speak during a lecture at Saarbrücken, he was interrupted by a group of protesters including advocates for the disabled. He offered the protesters the opportunity to explain why he should not be allowed to speak. The protesters indicated that they believed he was opposed to all rights for the disabled. They were unaware that, although Singer believes that some lives are so blighted from the beginning that their parents may decide their lives are not worth living, in other cases, once the decision is made to keep them alive, everything that can be done to improve the quality of their life should, to Singer's mind, be done. The ensuing discussion revealed that there were many misconceptions about his positions, but the revelation did not end the controversy. One of the protesters expressed that entering serious discussions was a tactical error.
The same year, Peter Singer was invited to speak in Marburg at a European symposium on "Bioengineering, Ethics and Mental Disability." The invitation was brutally attacked by leading intellectuals and organizations in German media, with an article in
Der Spiegel comparing Singer's positions to Nazism. The symposium was eventually cancelled and Singer's invitation consequently withdrawn.
A lecture at the Zoological Institute of the University of Zurich was also interrupted by two groups of protesters. The first group was a group of disabled people who staged a brief protest at the beginning of the lecture. They objected to inviting an advocate of euthanasia to speak. At the end of this protest, when Singer attempted to address their concerns, a second group of protesters rose and began chanting "Singer raus! Singer raus!" ("Singer out".) When Singer attempted to respond, a protester jumped on stage and grabbed his glasses, the host ended the lecture. The first group of protesters was distressed by this second, more aggressive group. It had not intended to halt the lecture and even had questions to ask Singer. Singer explains "my views are not threatening to anyone, even minimally" and says that some groups play on the anxieties of those who hear only keywords that are understandably worrying (given the constant fears of ever repeating the holocaust) if taken with any less than the full context of his belief system.