Peter Singer, the renowned ethical philosopher from Princeton University, has a scenario he asks his students (and the rest of us) to consider.

"If you saw a child in danger of drowning in a shallow pond, and all you had to do to save the child was wade into the pond and pull him out, would you do so?"

So far, no problem. All the students said they would. But Singer goes on.

"What if wading into the pond meant that you would ruin your most expensive pair of shoes?"

That wouldn't matter, the students insisted. A pair of shoes wouldn't count when it comes to saving a child's life.

But Singer, in his new book, The Life You Can Save, and also in his many appearances, essays and blogs, says that is what we do all the time, after a fashion.

We let children die for the price of a pair of shoes.

Princeton philosopher Peter Singer. (Denise Applewhite/Princeton University)

He reminds us that UNICEF estimates that 27,000 children die each day from preventable, poverty-related causes. People die from not having medicines that cost less than a dollar a day.

What's more, as columnist Brian Stewart reported recently, there are more than a billion people living in extreme poverty on this planet.

The good intentions of the UN Millennium Project are being tossed aside. Food riots are taking place. The catalogue of ills is almost numbing.

But Singer knows that people respond to stories about one person rather than statistics, which is why he tells his double-edged tale about the child in the pond.

Compare and contrast

Singer likes to compare and contrast. When you buy something you don't need — say, that extra pair of pants, or a $4 coffee — wouldn't you be better giving the cash to save real lives in the developing world?

Apparently not, at least as far as we charitable Canadians are concerned. According to a recent news story, Canadian contributions to charitable causes fell in 2008 to the lowest level in 40 years.

To this, Singer doesn't just give us the statistics and the obvious moral arguments.

He says he understands that there's a recession out there. He knows people feel constrained and fear that their donations will end up in Swiss bank accounts, put there by corrupt kleptocrats.

But Singer, who has been in the news recently for raising the issue of rights for robots, also has a rational plan to deal with at least some of these concerns and it is not all that punishing:

Give away as little as one per cent of your income if you make up to $100,000 and more after that, all graduated.

Another child

Of course, some wealthy people, such as Warren Buffett and Bill Gates, do give away millions.

And Singer himself donates one quarter of his income away to worthy agencies like Oxfam.

But he also knows there are many other psychological impediments to living the ethical life and here is where his examples get trickier.

Using the work of another philosopher, Peter Unger, he tells us another story.

"Bob is close to retirement. He has invested most of his savings in a very rare and valuable old car, a Bugatti, which he has not been able to insure."

Bob loves his Bugatti and takes care of it lovingly. But it's also an investment. When he retires he plans to sell it and live comfortably off the proceeds.

One day, while out for a drive, Bob parks his vintage car near the end of a seemingly unused railway siding. As he is strolling up the track, he sees a runaway train with no one on-board.

Further up the line he sees a child playing on the track. She is oblivious to the danger and she is too far away to hear him yelling.

The only way Bob can stop the train is to throw a switch that will divert the train to the siding, smashing his Bugatti in the process.

Now, faced with this decision, what would you do?

Luxuries have consequences

Remember, your retirement savings, something you have worked hard for all your life, are wrapped up in a beautiful vintage car, all gone for a child you don't know?

What would you do, save the child or the car?

In Unger's story, Bob thinks of his retirement and doesn't throw the switch, thus saving the car and killing the child.

Now, Singer says that most people, when asked, will choose to save the child they don't know, rather than the car.

That's because the child is a flesh and blood person, right in front of them. (Or maybe they want to be thought well of by the questioner?)

But Singer also tells us that, in a sense, we've already made Bob's choice: For in saving money for retirement, we are "effectively refusing to use that money to help save lives" now.

"This is a difficult implication to confront," the Australian-born Singer writes in his Psychology Today blog.

"How can it be wrong to save for a comfortable retirement? There is, at the very least, something puzzling here."

Put that way, both our retirement and our disposable incomes — our "luxuries" — can have serious, perhaps even deadly consequences for others.

Are you a monster?

Singer has many other examples like that, all designed to show that, while our moral intuitions are strong, our reasoning often isn't.

When confronted with a real, suffering person, we can sacrifice comforts and our prized possessions. But we won't do that at a distance. And that's not rational, according to Singer.

Because suffering or death from lack of food and medical care is bad. If it is in our power to prevent this, without sacrificing something important, it would be wrong not to do so.

By the same calculation, donating to aid agencies would relieve suffering. "Therefore," Singer's conclusion, "if you do not donate to aid agencies, you are doing something wrong."

Unfortunately, you may accept the reasoning and still not want to give up your discretionary income. You might just want to enjoy yourself.

Are you such a monster?

In a world where actors and sports figures can own vast numbers of cars and houses, and where outrageously rich people don't do their share, is it fair to expect ordinary people to donate what would be proportionately more than the callously wealthy?

That's the kind of "puzzling" question Peter Singer leaves us with. He doesn't scream at us. He's a philosopher, not a railing prophet.

But like any good philosopher, he can get us to ask questions about the way we live our lives.