The trolley problem, or, would you throw the fat guy off the bridge? A philosophical conundrum

Two books center on an enduring thought experiment and the moral considerations it raises. WOULD YOU KILL THE FAT MAN? The Trolley Problem and What Your Answer Tells Us About Right and Wrong By David Edmonds Illustrated. 220 pp. Princeton University Press. $19.95. THE TROLLEY PROBLEM; OR, WOULD YOU THROW THE FAT GUY OFF THE BRIDGE? A Philosophical Conundrum By Thomas Cathcart Illustrated. 132 pp. Workman Publishing. $14.95. you are walking near a trolley-car track when you notice five people tied to it in a row. The next instant, you see a trolley hurtling toward them, out of control. A signal lever is within your reach; if you pull it, you can divert the runaway trolley down a side track, saving the five - but killing another person, who is tied to that spur. What do you do? Most people say they would pull the lever: Better that one person should die instead of five. Now, a different scenario. You are on a footbridge overlooking the track, where five people are tied down and the trolley is rushing toward them. There is no spur this time, but near you on the bridge is a chubby man. If you heave him over the side, he will fall on the track and his bulk will stop the trolley. He will die in the process. What do you do? (We presume your own body is too svelte to stop the trolley, should you be considering noble self-sacrifice.) In numerical terms, the two situations are identical. A strict utilitarian, concerned only with the greatest happiness of the greatest number, would see no difference: In each case, one person dies to save five. Yet people seem to feel differently about the "Fat Man" case. The thought of seizing a random bystander, ignoring his screams, wrestling him to the railing and tumbling him over is too much. Surveys suggest that up to 90 percent of us would throw the lever in "Spur," while a similar percentage think the Fat Man should not be thrown off the bridge. Yet, if asked, people find it hard to give logical reasons for this choice. Assaulting the Fat Man just feels wrong; our instincts cry out against it. Nothing intrigues philosophers more than a phenomenon that seems simultaneously self-evident and inexplicable. Thus, ever since the moral philosopher Philippa Foot set out Spur as a thought experiment in 1967, a whole enterprise of "trolleyology" has unfolded, with trolleyologists generating ever more fiendish variants. (Fat Man was developed by the philosopher Judith Jarvis Thomson, in 1985.) Some find it frivolous: One philosopher is quoted as snapping, "I just don't do trolleys." But it really matters what we do in such situations, sometimes on a vast scale. In 1944, new German V-l rockets started pounding the southern suburbs of London, though they were clearly aimed at more central areas. The British not only let the Germans think the rockets were on target, but used double agents to feed them information suggesting they should adjust their aim even farther south. The government deliberately placed southern suburbanites in danger, but one scientific adviser, whose own family lived in South London, estimated that some 10,000 lives were saved as a result. A still more momentous decision occurred the following year when America dropped atom bombs on Hiroshima and Nagasaki on the argument that a quick end to the war would save lives - and by macabre coincidence, the Nagasaki bomb was nicknamed Fat Man. Similar calculations are being made right now. One has only to think of collateral damage in military strikes, or of the justifications offered for torturing terrorism suspects. At their best, such reasonings are valid; at their worst, they are a writhing nest of weasels. No wonder trolleyology now forms part of the philosophy course undertaken by cadets at West Point No wonder too that after several decades maturing in university philosophy departments, trolleyology has burst into the public eye with two books coming out at once. Both are jaunty, lucid and concise. Both explore an array of philosophical sources, from Aristotle and Aquinas to Bentham, Kant and Nietzsche. In "The Trolley Problem," Thomas Cathcart, a co-author of "Plato and a Platypus Walk Into a Bar ..." and other works, imagines a real-life trolley case on trial in the "Court of Public Opinion," a clever but slightly cumbersome device. In "Would You Kill the Fat Man?" David Edmonds, also a seasoned philosophy writer, tells the story more plainly, yet with wit and panache. Both books deal with difficult questions of reason and instinct, as well as with moral philosophy's scope and methods. Trolleyology has attracted the interest of practitioners of "x-phi," or experimental philosophy, who distinguish themselves from the "armchair" philosophers of old (that much-maligned piece of furniture), by borrowing empirical tools from sociology and psychology to find out what makes people tick. They stop short of laying out sections of trolley track under bridges, but they do use such resources as Harvard University's online Moral Sense Test, where some 200,000 volunteers have tried out their moral intuitions on a range of situations. One experiment at Michigan State University even used a virtualreality simulation. The results of such studies have been fascinating, showing, for example, that women are less likely than men to sacrifice the Fat Man, or even to flip the lever in Spur. Other investigations reveal that people are more likely to approve the killing of the Fat Man if they have just seen a comedy clip as opposed to "a tedious documentary about a Spanish village." The contingent nature of our ethical responses in general emerges from other research. We are more generous toward a stranger if we have just found a dime; a judge's decision to grant parole depends on how long it has been since he or she had lunch. Are these the "deep-rooted moral instincts" on which we are willing to found decisions that may affect tens or hundreds of thousands of fellow humans? Apparently our instincts only feel deep; in fact, they are fickle and easily manipulated. This malleability can be good or bad. Cathcart reminds us that many white people 150 years ago would have considered it instinctively obvious that black people were different and slavery was justifiable. Even a decade ago, many found it self-evident that gay people should not marry or have family lives. (A few still feel this, but now they have to argue their case rather than taking it for granted.) In both cases, rational moral arguments altered assumptions previously taken to be "just the way things are." This is one reason moral philosophers need not worry about being out of a job yet. A cool utilitarian calculus has its place, and so do our subrational instinctive juices. If either were missing, we would make some truly terrible choices. Yet there is also still room for that quaint seated figure, thinking through the principles and working out a kind of pragmatic yet justifiable wisdom. An armchair is also a useful place for reading books like these. With all this help, then perhaps when the trolley comes rattling around the corner, and with a half-second to decide, you might just do the right thing. Whatever that may be. Our instincts only feel deep; in fact, they are fickle and easily manipulated. SARAH BAKEWELL is the author, most recently, of "How to Live; Or, A Life of Montaigne in One Question and Twenty Attempts at an Answer," winner of the 2010 National Book Critics Circle Award for biography.