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A history of the "trolley problem" thought experiment.

Review of Would You Kill The Fat Man? The Trolley Problem and What Your Answer Tells Us About Right and Wrong. By David Edmonds. Princeton University Press. 220 pp. $19.95

You may well be familiar with this thought experiment: Standing on a footbridge overlooking a railway track, an observer sees a trolley hurtling toward five people tied to the rails. Next to her is a very fat man, who, if pushed onto the track, would stop the trolley before it reached the quintet. Would you – should you – kill one fat man to save five lives?

During the five decades since moral philosopher Philippa Foot, the granddaughter of President Grover Cleveland and the one-time roommate of novelist Iris Murdoch, introduced the first trolley conundrum, “trolleyology” (a neologism coined by Professor Kwame Anthony Appiiah) has become a cottage industry. The head scratchers often have exotic names: The Two Loop Case; The Extra Push Case; The Roller Skates Case; The Tractor Case; and the Lazy Susan Case. They are so diabolically complex as to “make the Talmud look like Cliff Notes.”

In Would You Kill the Fat Man?, David Edmonds, a senior research associate at the University of Oxford University’s Centre for Practical Ethics and the cofounder of the Philosophy Bites podcast series, provides a history of trolleyology. Informative, accessible, engaging and witty, his book is a marvelous introduction to debates about right and wrong in philosophy, psychology, and neuro-science.

Although trolley cases are abstract and artificial, Edmonds demonstrates that they have analogues in real life. During World War II, for example, the British government reduced the damage from German VI bombs by deceiving the Nazis (through false reports issued by double agents) into believing that the “doodlebugs,” most of which were missing the center of London, were hitting their marks. Although military leaders and Prime Minister Winston Churchill supported the operation, Herbert Morison, the minister for Home Security, was uneasy about “playing God,” and called attention to the likelihood of greater property damage and lives lost in areas of south London. Edmonds also cites the case of Captain Dudley, who was stranded with three other men in a lifeboat following a storm and a shipwreck, and killed one of them to provide food for himself and the others.

Because real life is full of “white noise,” making it difficult to identify “pertinent features of moral reasoning,” Edmonds suggests that carefully designed trolley scenarios can help “extract principles” by limiting the variables. And he enlists the distinction between intention and foreseeing, associated with Saint Thomas Aquinas, to address the conundrums posed by trolleyology. According to this theory, an act is justified if apart from its harmful effect it is in itself not wrong; the agent does not intend the harm, which is not large relative to the good being sought, as a means or an end; and there is no way to achieve the good without causing the harmful effects.

Therefore, Edmonds would divert a trolley into a loop on which one man was tied to prevent it from hurtling toward tracks on which five people were tied. The Doctrine of Double Effect, however, does not quite fit all cases. Acknowledging that utilitarian philosophers strenuously disagree, Edmonds would not push the fat man onto the track. Although they are hard put to explain why, he indicates, surveys reveal that about 90% of people agree with him.

A likely explanation is that feelings often trump reason. According to several studies, we’re more likely to be generous toward others if we are outside a bakery, smelling fresh bread, or have just found a dime in a phone booth. Presented with the Fat Man dilemma (described these days, Edmonds notes, as a “heavy” man, or better still, as a man with a heavy backpack), and the option of killing someone with your bare hands, parts of the brain associated with compassion go into overdrive, psychologists now believe, especially if the intended victim is someone you know or whose facial characteristics you can “see.” This “moral intuition,” born perhaps in an environment of evolutionary adaptation to interactions with other human beings (on whom our ancestors depended for survival), they argue, keeps us from defaulting to a utilitarian calculus.

Bolstered by recent developments in psychology, neuro-science, and experimental ethics, Edmonds concludes, the trolley industry is “in robust health.” It continues to help us comprehend our reactions, rational and emotional, to complex, richly imaginative, and yet also quite “real” scenarios, and get a better handle on the nature of morality. In the hands of a lucid explicator like David Edmonds, trolleyology is, at once, serious business (relevant, among others things, to preferences for drone strikes) and lots of fun.