From the outside, Worcester College, Oxford has the appearance of a rather dull provincial railway station, but enter through the porter’s lodge, past a spiral staircase on your left, and you immediately enter what I regard as Oxford’s most beautiful quad. Well, it’s a three-sided quad, if that’s not a contradiction. There are mediaeval cottages to your left, an imposing 18th century neo-classical building to your right, while ahead the view is all trees and woodland. 

The gardens are accessed through a small gap on the far left. And when I studied at Worcester College in the 1980s, the story was that this had somehow inspired Lewis Carroll, when he wrote Alice in Wonderland. That’s probably an Ivory Tower myth, but the Australian philosopher Peter Singer says that the lake, which lies just beyond the opening, may have triggered his famous thought experiment. 

It goes something like this:

You are walking past a shallow pond when you see a child struggling in the water. There is no one else around—no parent or guardian. You are about to wade in to save the child, when you notice that you are wearing your most expensive new shoes, and there’s no time to remove them. Shoes or kid?

Of course, this is not a serious question. Only a moral monster could believe that ruining their shoes should be a factor in whether to rescue the child. But Singer’s controversial claim is that those of us who are comfortably off in the affluent west are, in effect, walking past such a shallow pond every day of our lives. We could easily donate money—money that we would barely miss—to an international development charity that could use it to save lives.

Origins of the Shallow Pond

It’s arguably the most influential thought experiment in moral philosophy. Not only is there a significant philosophical literature that directly addresses it, but it has escaped the confines of academia and inspired the worldwide Effective Altruism movement—which encourages members to give 10% of their income to the most effective charities.

But the impact of the Shallow Pond was far from immediate. The argument took decades to seep into the non-philosophical world, after first appearing in print in 1972 when Singer was still in his twenties. He had arrived in Oxford three years earlier, to study for the prestigious BPhil., after growing up in Melbourne, Australia, the son of two refugees from Vienna. (His four grandparents all perished in the Holocaust.)  

After completing his degree, he successfully applied for a two-year lectureship at University College. One of his colleagues was the legal scholar Ronald Dworkin, who was on the board of a new journal, Philosophy and Public Affairs. Dworkin approached Singer: would he be interested in contributing an article?

This was a tumultuous period; the rise of feminism, the civil rights movement, and the rapid increase in immigration were reshaping western democracies. There were debates about legalizing homosexuality and abortion, and the outlawing of capital punishment. Philosophers were unaccustomed to engaging in contemporary affairs, at least in their scholarly work, but many now felt that such dramatical societal upheaval could not be ignored. Hence the new journal.

It was an equally turbulent time on the international stage. The Vietnam War was the dominant issue in the West, but in the late 1960s there was a catastrophic civil war in Nigeria, tension was brewing in Northern Ireland, and in 1971 Idi Amin seized power in Uganda—the expulsion of the Asian community would follow. But the events that most exercised Singer were taking place in what we now call Bangladesh.

With the British withdrawal from India in 1947, a majority Muslim country, Pakistan was forged from two separate areas more than 1,000 miles apart. East Pakistan (Bangladesh) was the poor relation, and in 1971 it sought independence. The resulting war led to millions of desperate people streaming across the border to India. The makeshift camps in India were inadequate; disease was rampant, and many refugees died from malnourishment. Singer read about their plight in the vivid reporting of the Sunday Times. And it got him thinking: what did people like him owe to these needy, distant strangers?

Although Singer had arrived in the UK already committed to utilitarianism—crudely put, the view that we should act so as to maximize happiness and minimize pain—the simple principle he came up with when reflecting upon the situation in Bangladesh did not rest on a purely utilitarian premise.  It was this: “If it is in our power to prevent something bad from happening, without thereby sacrificing anything of comparable moral importance, we ought, morally, to do it.” The shallow pond illustrated this principle.

The uncanny power of thought experiments

It is notoriously difficult to define a thought experiment. But, broadly put, they’re imaginary scenarios that are usually employed in philosophy to clarify or test a theory, or to try get us to think about an aspect of the world in a novel way. 

Many philosophers have a strong and instinctive resistance to thought experiments, in a way that I find intriguing and which often, it seems to me, has no rational basis. In fact, the history of philosophy is inextricably linked to thought experiments. Reflecting on human nature, Plato discusses the Ring of Gyges – a ring that makes it wearer invisible. Descartes imagines an evil demon who deceives me into believing that there is an external world. Almost every philosopher of note, including Locke, Hume, Rousseau and Nietzsche have conjured up thought experiments of their own.

In the twentieth century, however, it’s notable that all the best-known thought experiments, including Peter Singer’s, came in the back half. I have an unsubstantiated theory about this. In the 1920s and 1930s, a dominant strain in philosophy was logical positivism, promulgated by the Vienna Circle. The logical positivists maintained that for a proposition to be meaningful it either had to be verifiable (there had to be ways of testing it), or it had to be true by definition. So, ‘All bachelors are smelly’ and ‘All bachelors are unmarried men,’ are both legitimate (meaningful), even if the first is untrue.

But with rare exceptions, philosophical thought experiments are neither testable nor true by definition. The statement, “The bystander was wrong to ignore the screams of the child in the shallow pond” fails both criteria. It is certainly not true by definition; nor can it be tested in any scientific sense. Logical positivism became largely discredited in the aftermath of World War II. But in the first half of the century its sway over the discipline may have been enough to deter would-be thought experimenters. 

Objections

While it seems perverse to condemn thought experiments as a whole, moral thought experiments are regarded as particularly problematic. Various attacks have been directed at them. Here are three.

First, there’s a moral or perhaps aesthetic objection. The territory of moral thought experiments is one in which suffering and death are habitual, and there’s a sense in which those who discuss these scenarios are frivolous, treating them as a sort of game or puzzle. In a variation of the Trolley Problem, you can push a large man to his death by toppling him over a footbridge, thereby saving five lives. In other thought experiments there are ticking bombs that will only be defused if torture is inflicted on the bomber. And so on. 

Perhaps this is true of some, but it would seem unfair to accuse Peter Singer of glibness. He’s a thinker whose philosophical conclusions have profoundly shaped the way he lives his life—including giving away a large proportion of his income to charity.

A second objection is that moral thought experiments are often surreal, and that our intuitions about them are therefore unreliable, because they have been developed to cope with normal situations. Take Judith Jarvis Thomson’s violin thought experiment, published in the first volume of Philosophy and Public Affairs. You wake up one morning to find yourself in a hospital bed next to a stranger who’s attached to you with various tubes. It turns out that he’s a famous violinist who was in danger of dying due to kidney failure. You alone had a blood type that could save him—and so you were seized by the Society of Music Lovers, and without your consent, connected up to him. You could unplug yourself, but then the musician would die. Still, don’t worry, says an official in a white coat, it’s only for 9 months—by then the violinist will be healed. What should you do?  Thomson uses this hypothetical set-up to make the case for the legitimacy of abortion. But its bizarreness might make you question how your response would relate to the real world.  

There’s much more that could be said about this critique, and in defense of bizarre scenarios, but note that it doesn’t apply to all moral thought experiments. There’s nothing especially weird about Singer’s drowning child for example. Unfortunately, people drown in pools, lakes and seas every day.

A third objection is more fundamental. And that is that moral judgements are necessarily made within a particular and intricate setting. It is impossible to determine from Scenario A, what one should do in Scenario B, since every situation is unique. But it’s difficult to know how much weight to give this point, since, if true, it would be virtually impossible to debate ethical issues, and much ethical philosophy would be rendered futile.  

Enduring Influence

Thought experiments are not arguments, though they may accompany arguments. Yet because they can be so vivid, and often contain a narrative element, they can make an enduring impression. In that sense, one of the skills needed to create a good thought experiment is literary rather than philosophical. Philosophy can get highly technical. There are many seminal papers where the details of the argument are largely forgotten, but the gist of it, conveyed through a thought experiment, survives. 

Judith Jarvis Thomson’s Violin scenario is germane in this regard. She wanted to make the case that, even were we to concede that a fetus has the same moral status as an adult human, a woman would still have no obligation to allow her body to be used for the benefit of somebody else. It is entirely irrelevant that the attached person in the hospital is a famous violinist. He could equally have been a bricklayer, a realtor or an accountant. But who, having read her paper, could ever forget the Society of Music Lovers! 

There’s a parallel explanation for the lasting appeal of “Famine, Affluence, and Morality.” Singer did not need the image of the man with expensive shoes passing a drowning child to make his point. It was merely an illustration of his argument. Yet it’s the bit that everyone remembers. And it’s quite possible that without it, the paper would have shared the fate of 99.9% of other philosophy papers and disappeared into obscurity. 

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David Edmonds is the author of Death in a Shallow Pond: A Philosopher, a Drowning Child, and Strangers in Need (Princeton University Press)