Peter Singer, an applied ethicist, is one of the world’s best-known philosophers. His new book, The Life You Can Save (Random House, $22), argues that it is ethically indefensible not to donate a certain portion of your wealth to NGOs and aid groups fighting extreme poverty around the world ( Such inaction, he says, is like walking past a child drowning in a pond. –Christine Smallwood

Why not institute a compulsory tax rather than rely on NGOs?

If you’re asking about the United States, it’s because the US is not very effective in its aid program. NGOs really do have a better record of working more with the grassroots, of not going through governments and not making the governments dependent on them. If we were in Sweden, maybe there would a better, less politically directed aid program where a compulsory tax might be a reasonable option.

Are vastly unequal distributions of global wealth ineradicable?

We don’t have a better system of encouraging people to be productive in ways that are useful for others. In theory, if you were to sketch out, as people did in the nineteenth century, utopian blueprints of how our society should function, then obviously you would have a more equal distribution of wealth. But insofar as we’ve ever tried those things, they don’t work. I don’t think you can criticize people for being rich if what they have done is effectively produce things that people want or produce them more cheaply than other people have done. Those are good things to do. I don’t see the problem with getting rich in the first place. I see a problem with getting rich and not seeing that as an opportunity to do an immense amount of good in the world. There’s always going to be relative poverty. I don’t think we’re going to get rid of that, due to the nature of the system of production that we have. But I don’t think there has to be this constant state where there are a billion people living in extreme poverty, even in countries that don’t have terribly repressive governments.

How does one know when to stop giving?

That’s the most difficult question. On the one hand, there’s this very demanding implication of my original argument, that as long as I have something that’s a luxury that I don’t need and the money I spend on it could save a child’s life, I should really keep giving until I don’t spend anything on luxuries at all. I still see the pull of that argument. But it’s also important to think about what we would achieve by setting that as the standard–we would not achieve nearly as much. In that sense, the answer is something like, we should give to the point where if others gave similarly, we would be able to more or less solve the problem. And we should feel OK if we reach that standard and encourage others to reach it, because that will produce the best results.

Why don’t people give more than they do?

There are a lot of reasons. There are the psychological factors–people give to identifiable individuals more readily than they give to a statistical mass. Or they help when they fear that they alone are responsible rather than when responsibility is diffuse. They give when they believe that others are giving. And if they don’t see others helping, not very many will do very much. But if we can change that perception, you could get a virtuous reinforcing spiral where people give because they see others are giving.

Is it better to send money abroad than to donate money to a local homeless shelter?

Your dollars go a lot further in developing countries. For $50 you can restore someone’s sight in Eritrea; for $400 you can repair an obstetric fistula for a girl in Ethiopia. And I don’t think these sorts of sums can do anything nearly as life-changing in our country. To help a homeless person on the streets of New York City is a long and complicated and quite expensive process, really.

You’re a utilitarian. Utilitarianism tries to maximize the net surplus of happiness over misery in the world. What if billionaire Larry Ellison’s yacht makes him really, really happy?

This is what some call the utility monster argument. We would have to assume that Larry Ellison actually has capacities for happiness that are vastly greater than anyone else’s. Ellison’s yacht cost $200 million, and if we assume that $400 can repair an obstetric fistula, that means that the suffering relieved by 500,000 obstetric fistula repairs is not greater than the happiness that Ellison gets from his yacht. That, I think, is not physically possible. But if we ever encountered Martians who could convince us that they had a vastly greater capacity for happiness than we do, then it could be a problem.

Then the moral position would be to let the Martians colonize Earth and make us their slaves.

Yes, that does seem to be the implication of the theory. A lot of people do think that’s a damning objection to utilitarianism.

Does your standard of giving advocate a kind of asceticism?

Not for its own sake. Some forms of indulgence and expensive pleasures are difficult to justify in a world in which 27,000 children [younger than 5] die daily of forces you could help prevent. Maybe the amount of money that we’re spending on symphony orchestras or buying a Duccio for the Met is not a good priority at the moment. But I would love there to be a world in which there weren’t such urgent needs for our resources and we could say, OK, we’ve dealt with all those really urgent problems; now let’s go back to enjoying our symphonies and our medieval paintings.