“WOULD You Kill the Fat Man?” is the title of a recent book about a set of moral problems that philosophers like to ponder, and psychologists to put to their experimental subjects. In the canonical form, you are on a footbridge watching a trolley speeding down a track that will kill five unsuspecting people. You can push a fat man over the bridge onto the tracks to save the five. (You cannot stop the trolley by jumping yourself, only the fat man is heavy enough.) Would you do it?

Most people quail at the idea of shoving the man to his death. But alter the scenario a bit, and reactions change. People are more likely to throw a switch that would divert the trolley on to another track where it will kill only one person. The utilitarian calculation is identical—but the physical and emotional distance from the killing makes throwing the switch much more popular than throwing the man.

There are other ways to nudge people’s judgments, too. A rather counter-intuitive one was reported in a paper published last month in PLOS ONE, a journal. In it, Albert Costa of the Universitat Pompeu Fabra in Spain, and his colleagues, found that the language in which the dilemma is posed can alter how people answer. Specifically, when people are asked the fat-man question in a foreign language, they are more likely to kill him for the others’ sake.

Dr Costa and his colleagues interviewed 317 people, all of whom spoke two languages—mostly English plus one of Spanish, Korean or French. Half of each group were randomly assigned the dilemma in their native tongue. The other half answered the problem in their second language. When asked in their native language, only 20% of subjects said they would push the fat man. When asked in the foreign language, the proportion jumped to 33%.

Dans le jardin of good and evil

Morally speaking, this is a troubling result. The language in which a dilemma is posed should make no difference to how it is answered. Linguists have wondered whether different languages encode different assumptions about morality, which might explain the result. But the effect existed for every combination of languages that the researchers looked at, so culture does not seem to explain things. Other studies in “trolleyology” have found that East Asians are less likely to make the coldly utilitarian calculation, and indeed none of the Korean subjects said they would push the fat man when asked in Korean. But 7.5% were prepared to when asked in English.

The explanation seems to lie in the difference between being merely competent in a foreign language and being fluent. The subjects in the experiment were not native bilinguals, but had, on average, begun the study of their foreign language at age 14. (The average participant was 21.) The participants typically rated their ability with their acquired tongue at around 3.0 on a five-point scale. Their language skills were, in other words, pretty good—but not great.

Several psychologists, including Daniel Kahneman, who was awarded the Nobel prize in economics in 2002 for his work on how people make decisions, think that the mind uses two separate cognitive systems—one for quick, intuitive decisions and another that makes slower, more reasoned choices. These can conflict, which is what the trolley dilemma is designed to provoke: normal people have a moral aversion to killing (the intuitive system), but can nonetheless recognise that one death is, mathematically speaking, better than five (the reasoning system).

This latest study fits with other research which suggests that speaking a foreign language boosts the second system—provided, that is, you don’t speak it as well as a native. Earlier work, by some of the same scholars who performed this new study, found that people tend to fare better on tests of pure logic in a foreign language—and particularly on questions with an obvious-but-wrong answer and a correct answer that takes time to work out.

Dr Costa and his colleagues hypothesise that, while fluent speakers can form sentences effortlessly, the merely competent must spend more brainpower, and reason much more carefully, when operating in their less-familiar tongue. And that kind of thinking helps to provide psychological and emotional distance, in much the same way that replacing the fat man with a switch does. As further support for that idea, the researchers note that the effect of speaking the foreign language became smaller as the speaker’s familiarity with it increased.

Regardless of the exact mental mechanism behind the team’s findings, they could have big implications. Boaz Keysar, a psychologist at the University of Chicago and one of the study’s authors, talks of investigating the impact on medical or legal decision-making. Meanwhile, globalisation is boosting the number of bilinguals. There are more non-native English speakers (500m, by one estimate) than native ones (perhaps 340m). Big firms are making English their internal language, even if it is not the native tongue of most of their workers. Meetings of international organisations like the United Nations or the European Union are often conducted in languages that are not the preferred ones of most of those attending. Perhaps it is reassuring to think they may be more coolly rational than meetings of monoglots—unless, that is, you are the metaphorical fat man about to be pushed under a train.