Simon is an admirer of the author-philosopher Peter Singer, the longtime Princeton University professor whose The Life You Can Save has been a guide for Simon and others looking for ways to donate money.

Singer has completed a new edition of the book, which comes out this week, and Simon is helping with the promotion. He read a chapter for the audio edition and sat with Singer recently for an Associated Press interview. "I'm very comfortable with Peter's way of thinking," Simon explains.

In The Life You Can Save, first published in 2009, Singer is both high-minded and pragmatic. He considers the obligations we have to each other and how to expand our compassion for those we know to people we've never met.

In the book and on www.thelifeyoucansave.org, he lists specific organisations, from Oxfam to Village Enterprise, that have been independently audited and recommended. He also probes the morality of giving, how much is expected of each of us, and addresses criticism on whether philanthropy is simply a way for the rich to improve their images and maintain power.

"If you ask me, 'Should there be an economic system in which nobody becomes a billionaire', I would say yes," Singer says. "But if you say, 'In the world as it is, is it immoral for people to be a billionaire', I would have to say no, because I know people who are giving away - like Warren Buffett - most (of their money). I think that's perfectly reasonable."

Simon, 78, and Singer, 73, spoke at Simon's midtown Manhattan office suite, in a room that showcases Simon's successes and passions, including shots of Simon with historical figures such as Nelson Mandela and the Dalai Lama. He and Singer are both world citizens who might share stories about the Amazon forest or East Timor, or Singer's native Australia, where he saw Simon perform decades earlier.

They met in 2005, when Singer was among the honourees at a Time magazine gala for the world's "100 most influential people".

"I went up to Peter," Simon recalls. "I was familiar with Peter, with his work, and I introduced myself and then we said, 'Let's get together'."

"You and (Simon's wife) Edie (Brickell) came to dinner," Singer adds. "Then we met when you were in Australia."

Simon and Singer have a warm, sometimes teasing rapport ("I can't say it was a real page turner," Simon says jokingly about The Life You Can Save), strong enough that they can differ over what Simon calls Singer's "hierarchical priorities". Singer believes that, with so many urgent problems in the world, grand cultural projects such as art galleries and opera houses should hold far lower standing for would-be donors.

"Once we had a long walk along the beach in Melbourne," Simon explains, "and I said, so if we went down the list of what you would say is the most important places to make your contribution, in that way of thinking you would say that a donation to the Metropolitan Museum of Art would really be at the bottom of the list."

"Close to it, anyway," Singer says.

"I said, 'I disagree with that'," Simon recalls. "I think that while we have an obligation to raise the lowest up to a point where they are being treated humanely, we also have an obligation to honour the creativity of what humans do at the highest level. That's also an expression of humanity."

"It's not that I don't value, of course, the creativity of humanity, and some of the great works that have been achieved. And I'm glad that they're preserved," Singer answers. "I also think that in a world that has so much present human need, that that (need) should be the priority ... When the Met buys a painting, it's not as if that painting would have been left out to rot had they not bought it."

Simon stopped touring in 2018 and laments - without naming names - that some of his wealthy contemporaries continue to make substantial amounts of money from concerts instead of using it to help others. He still performs live, but donates profits to a variety of causes, whether for treating fistula, a condition afflicting millions of African women that Simon learned about through Singer, or for the environment, which he considers the most urgent problem.

Simon had been giving, and raising, money well before he knew of Singer. In the early 1970s, he was among the performers at a concert for Democratic presidential candidate George McGovern. He sang on the all-star "We Are the World" recording from 1985 and a few years later helped found the Children's Health Fund.

But he is also wary of events that fail to help the intended people. Simon found that compassion wasn't enough; he had to investigate first hand where the money went. He remembers being in Biloxi, Mississippi, in 2005, after Hurricane Katrina. He was there with a mobile medical unit, looking for community leaders who could help connect them with people in need of help.

"You really have to know what and to whom you're giving this money," he says. "All these years I had been doing these benefit concerts with all my friends and musicians. We'd come. We'd play. We pack up our guitars. We leave. And nobody ever says, 'Where'd that money go?'"