The trolley problem is a series of thought experiments in ethics and psychology, involving stylized ethical dilemmas of whether to sacrifice one person to save a larger number. The series usually begins with a scenario in which a runaway tram or trolley is on course to collide with and kill a number of people (traditionally five) down the track, but a driver or bystander can intervene and divert the vehicle to kill just one person on a different track. Then other variations of the runaway vehicle, and analogous life-and-death dilemmas (medical, judicial etc.) are posed, each containing the option to either do nothing, in which case several people will be killed, or intervene and sacrifice one initially "safe" person to save the others. Opinions on the ethics of each scenario turn out to be sensitive to details of the story that may seem immaterial to the abstract dilemma. The question of formulating a general principle that can account for the differing judgments arising in different variants of the story was raised in a 1967 philosophy paper by Philippa Foot, and dubbed "the trolley problem" by Judith Jarvis Thomson in a 1976 article that catalyzed a large literature. Thus, in this subject the trolley problem refers to the meta-problem of why different judgements are arrived at in particular instances, which are called trolley cases, examples, dilemmas, or scenarios. The most basic version of the dilemma, known as "Bystander at the Switch" or "Switch", goes: There is a runaway trolley barreling down the railway tracks. Ahead, on the tracks, there are five people tied up and unable to move. The trolley is headed straight for them. You are standing some distance off in the train yard, next to a lever. If you pull this lever, the trolley will switch to a different set of tracks. However, you notice that there is one person on the side track. You have two (and only two) options: Do nothing, in which case the trolley will kill the five people on the main track. Pull the lever, diverting the trolley onto the side track where it will kill one person. Which is the more ethical option? Or, more simply: What is the right thing to do? Philippa Foot introduced this genre of decision problems in 1967 as part of an analysis of debates on abortion and the doctrine of double effect.[1] Philosophers Judith Thomson,[2][3] Frances Kamm,[4] and Peter Unger have also analysed the dilemma extensively.[5] Thomson's 1976 article initiated the literature on the trolley problem as a subject in its own right. Characteristic of this literature are colorful and increasingly absurd alternative scenarios in which the sacrificed man is instead pushed onto the tracks as a weight to stop the trolley, has his organs harvested to save transplant patients, or is killed in more indirect ways that complicate the chain of causation and responsibility. Earlier forms of individual trolley scenarios antedated Foot's publication. Frank Chapman Sharp included a version in a moral questionnaire given to undergraduates at the University of Wisconsin in 1905. In this variation, the railway's switchman controlled the switch, and the lone individual to be sacrificed (or not) was the switchman's child.[6][7] German philosopher of law Karl Engisch discussed a similar dilemma in his habilitation thesis in 1930, as did German legal scholar Hans Welzel in a work from 1951.[8][9] In his commentary on the Talmud, published long before his death in 1953, Avrohom Yeshaya Karelitz considered the question of whether it is ethical to deflect a projectile from a larger crowd toward a smaller one.[10] Similarly, in The Strike, a television play broadcast in the United States on June 7, 1954, a commander in the Korean War must choose between ordering an air strike on an encroaching enemy force at the cost of his own 20-man patrol unit, or calling off the strike and risking the lives of the main army made up of 500 men.[11] Beginning in 2001, the trolley problem and its variants have been used in empirical research on moral psychology. It has been a topic of popular books.[12] Trolley-style scenarios also arise in discussing the ethics of autonomous vehicle design, which may require programming to choose whom or what to strike when a collision appears to be unavoidable.[13]
