Peter Singer is a Utilitarian, a philosopher who believes we should strive in our actions to maximize the amount of happiness in the world. Singer is said to measure morality by the numbers—one of his most infamous examples being that, sometimes, the way to maximize happiness is to allow parents of infants born with severe, life-threatening disabilities the option of euthanization. His comparison between the choices we make about fetuses inside the womb and the choices we ought to be able to make with certain newborn infants produced protests, physical threats, and talk of armed security to guard his Princeton office.

He’s also been attacked from inside the ivory tower. Some philosophers don’t think much of ideas that are accessible enough to have practical import. Yet despite some efforts to dismiss Singer’s work, his primacy in university life is undeniable. His Practical Ethics and Animal Liberation are used extensively in ethics classes, and his ideas appear regularly in seminars and conferences. This is because, with a zeal that suggests he’s computing the moral significance of every passing minute, Singer tackles the hard questions of the day; from research on cloned embryos, to the use of animals in food and research, to famine in India and AIDS in Africa. Invariably, his conclusions threaten our moral aplomb by relentlessly demonstrating the ways in which it’s not nearly enough that we empty our pockets to the homeless we pass on the streets, that we don’t shop at Wal-Mart, that we’re on the wait list for a Toyota Prius, or even that we recycle our soy-milk cartons. He argues that we must do much, much more, donating enough of our income to poor, developing nations so that wealth is more evenly distributed globally, even if it involves a drastic reduction in our standard of living.

His critics argue that things are not so simple, that his arguments don’t take into account special relationships and going to the opera. Here, Peter Singer responds to some of these criticisms, as well as to questions on his views about the duties of U.S. citizens, the state of the animal rights movement, and his most recent book, The Moral of the Story: An Anthology of Ethics Through Literature, coedited with his novelist wife, Renata Singer.

—Sahar Akhtar

I. “WHILE PEOPLE ARE DYING BECAUSE THEY DON’T HAVE SAFE DRINKING WATER, OR CAN’T GET EVEN THE MOST MINIMAL HEALTH CARE, OR SEND THEIR CHILDREN TO SCHOOL, I THINK SUPPORT FOR THE ARTS HAS TO COME SECOND.”

THE BELIEVER: One of your positions in One World echoes the position you took in “Famine, Affluence, and Morality”: that citizens of developed nations...