So, where have we traveled so far? Singer has argued that 1) we have a moral obligation to help those who lack access to sufficient food, shelter, and medical care and 2) that we can do this by donating to aid agencies. Assuming we agree with him, how much should we give? Part 4 tries to tease out an answer in detail.

On its face, the book’s argument seems to imply a pretty demanding level of giving. After all, I could deprive myself of a lot of luxuries (and donate the money saved to aid agencies) before being in danger of not having enough to adequately meet my own needs and those of my family. Are we then obliged to sacrifice everything beyond what we need to live more or less comfortably for the sake of helping the very poorest people of the world? Singer admits that the logic of his argument seems to point in this direction, but he also knows that many (perhaps most) of us would balk at such an extreme conclusion and, human nature being what it is, maybe decide not to give anything at all. If such seemingly onerous sacrifices are called for, we might say, then there must be some flaw in Singer’s reasoning.

Singer presumably doesn’t think his own reasoning is flawed, but he offers a kind of compromise position as a public standard that he thinks most people can aspire to, but which can still make a huge difference. To this end, he proposes percentages that people in the top ten percent of the U.S. income distribution should give to aid. Those making more than about $105,000 a year should give 5% of their income away; those making over $148,000 should give 10%; more than $383,000, 15%; over $600,000, 20%; and over $1.9 million, 25%. To avoid dis-incentives to move to a higher bracket, this standard could be made more progressive – e.g., someone making $500,000 would give away 5% of the first $148,000; 10% of the next $235,000; and 15% of the remainder.

The amount of money this would raise–from affluent, or at least comfortable, people in the U.S. alone–is about $471 billion a year. For comparison’s sake, Jeffrey Sachs, author of The End of Poverty, estimates that it would cost $189 billion a year to meet the UN’s Millennium Development Goals. (Bracketing for the moment the question of how effective the MDGs themselves are.) Singer adds that there’s no reason to think that people in the bottom 90% of the income scale can’t also give something; if they gave just an average of 1% of their income, this would add about another $40 billion. While it’s obviously difficult to generalize about how much any of us can give, which will depend a lot on circumstances, when I did the math it was pretty clear that I could give according to Singer’s scheme without being seriously deprived.

As is often the case with Singer, there’s a tension between what consequentialist morality seems to require of us and what our own particular attachments–to our family, friends, compatriots, etc.–seem to demand. This isn’t to say that Singer opposes all particular attachments; he thinks there are good (consequentialist!) reasons for preferring that parents raise their own children rather than society trying to institute some kind of communal parenting arrangement. But many of us will balk at this rather cold-blooded argument. It just seems right, we say, that we should prefer our own children to the children of others.

But you don’t need to buy completely into Singer’s utilitarianism to feel the force of his argument. Even granted that we have special duties to our own kith and kin, isn’t there some point at which showering them with luxuries seems grotesque given the magnitude of human suffering in the world? Is it really OK to spend tens of thousands of dollars to send your kid to a fancy private school, or to buy him a new car for his 16th birthday, or send him on a European vacation when there are millions of children in the world who lack access to the basic necessities of life? Surely our particular duties to those we love don’t trump all claims that others might have on us.

The book ends with a consideration of how giving to others can be a way of finding meaning in one’s own life. He cites ancient wisdom and modern research to suggest that helping others is actually a source of deep satisfaction. It almost goes without saying that, from a Christian perspective, it’s well-attested that it is better to give than to receive.

Whatever else Singer has accomplished here, I think he has, at the very least, put the burden of proof on those who deny that we have obligations to do a lot more than we currently are to alleviate world poverty. The fact that this often barely registers as a blip on our political or personal radar screens is a scandal. There are groups doing good work that make a difference in people’s lives, even if it’s sometimes difficult to say how much difference they’re making. And the sacrifice required for most of us to make a significant difference would be comparatively small.