Would You Kill the Fat Man? by David Edmonds Princeton 3 stars David Wilson This provocatively titled tract opens with a burst of drama that proves philosophy can be exciting. "This book is going to leave in its wake a litter of corpses and a trail of blood. Only one animal will suffer within its pages, but many humans will die." In particular, a heavyset man may fall from a footbridge, radio journalist David Edmonds writes. Would You Kill the Fat Man? centres on a classic philosophy puzzle introduced by British philosopher Philippa Foot in 1967 and dramatically modified by American moralist Judith Thomson. In Thomson's version, a runaway train is barrelling towards five men tied to the track. Standing on a footbridge, you watch the evolving disaster. Beside you, a fat stranger lurks, posing a dilemma. Push him off the bridge and he will land on the line and die, but his bulk will stop the train, saving five lives. What do you do? In various forms, the dilemma dubbed "the trolley problem" - in a nod to the American word for tram - has preoccupied philosophers for decades, also ensnaring psychologists and neuroscientists. Most sources judge killing the fat man wrong, but they might be misguided because his loss would save lives, Edmonds says, showing how tricky "trolleyology" is, with the help of diagrams. According to the blurb, Edmonds' investigation also shows how much trolleyology matters. One crucial dilemma he gauges relates to the second world war British prime minister Winston Churchill, who tried to trick the Nazis into dropping bombs south of central London. Probably, the ploy meant that fewer British civilians died overall, but it was bad news for South London residents. Cue fraught debate between Churchill and one of his top ministers, which trolleyology enthusiasts may continue. The perplexing branch of philosophy can be applicable to modern conflict, too. Take the case of Bangkok's Chao Phraya river swelling to bursting point in 2011. To save the town centre, the authorities built a 15-kilometre-long dam, which kept the city dry but caused a build-up of water beyond its bounds. Enraged suburbanites demanded that the dam be modified to let the swelling, stagnating water flow through, only to be snubbed, rightly or wrongly. The Thai tale is a familiar modern trolleyology puzzle, according to Edmonds, a BBC World Service radio feature maker. The ethical intricacies he explores in his fat man treatise will fuel scholastic fascination, he claims. True, morality is important. Yes, Edmonds is a suave stylist. Still, at a time of spiking temperatures and sharpening social inequality, the slant of his moral manual may strike some readers as trivial, parochial, even geeky. As Edmonds admits, the many train track variants he charts can be dismissed as "harmless fun - crossword puzzles for long-stay occupants of the Ivory Tower".