So, the other day I was strolling past the murky Whitestone Pond, at the top of Hampstead Heath, when I saw a small girl who’d slipped and fallen in, and was desperately struggling to keep her head above water. There was nobody else around to help and perhaps I should have waded in. But the problem was that I was wearing my brand new, slim-fit, cotton Ralph Lauren shirt, retailing at £185. I was damned if I was going to let that be ruined. So I just carried on along my way. Condemn me if you will, call me callous, but as fellow fashionistas will surely understand, a Ralph Lauren shirt is a Ralph Lauren shirt…

Relax, readers, that didn’t actually happen. For one thing, I’d never cough up £185 for a shirt (I’m more of an M&S man myself). And, for another, I’d like to believe that if I did see someone drowning in real life, I’d jump in. Were a person to watch as someone died out of concern for a chic jacket or posh frock, they would, rightfully, be subjected to outrage.

And yet, as the Australian philosopher Peter Singer points out, walking past the drowning child is, metaphorically, what we do every day. There are many parts of the world where £185 would make a massive difference and where efficient charities exist that could effectively channel our money to save life.

Singer espouses a pure version of utilitarianism, the theory that actions are to be judged solely by their consequences. The best action is that which, crudely put, causes the most happiness after subtracting for any suffering.

As a strict utilitarian, he rejects any intrinsic moral distinction between helping those geographically close at hand, and helping those far away.

More counter-intuitively, he rejects the distinction between what we do, and what we fail to do, in philosophic terminology, between an act and an omission. At root, taking a life and failing to save a life are morally on a par, since both result in a death. That has far-reaching implications for how much we give to charity — he himself gives away at least a third of his salary, though he concedes that, on his own account of ethics, he should do even more.

He also denies the intrinsic importance of the distinction between intending to do something and merely foreseeing it. For example, in warfare, to engage in an operation intending to kill civilians is always legally and morally outlawed. But it is sometimes deemed acceptable to attack a target (a munitions factory, say), even if it is foreseen that civilians living nearby will be killed as a side effect — in “collateral damage”, to use that terrible euphemism. For Singer, if you predict 100 civilians will die, it is immaterial whether you actively intend or just foresee the consequences of your action.

Singer’s utilitarianism, combined with a particular view about what gives us our moral status (namely, our sentience and, in particular, our capacity to feel pain), has led to his embracing of, and campaigning for, some highly contentious positions, including on animals (he’s effectively the founder of the international animal-rights movement), euthanasia and on infanticide of the seriously disabled. He sees no important difference between the foetus in the womb at the end of a pregnancy and the baby that emerges a few minutes later.

This has led some people to call him “dangerous” and others to go further, branding him a Nazi, an appalling and absurd calumny, and particularly ironic given his background as the son of Viennese Jewish refugees. (He’s written a book about his grandfather, David Oppenheim, a psychoanalyst and close collaborator of Freud’s who died in Theresienstadt.) More reasonable critics, who regard Singer’s arguments as extreme, still acknowledge their rigour.

They’re thought-provoking, too. After reading Singer, it would be hard not to reflect, before purchasing your designer brogues, that the money spent could, almost certainly, be put to better use.

If you only read one Singer book, make it The Life You Can Save (Picador 2009)

@DavidEdmonds100