Trolley problem

The trolley problem is a thought experiment in ethics centered on a runaway trolley, five people on the main track, and one person on a side track. It asks whether pulling a lever to divert the trolley is the correct choice, and it has become a standard way to test moral judgment.

The page presents several related cases and the reactions they trigger. These include Foot’s original formulation, the fat man, the fat villain, the loop variant, the transplant case, and Unger’s man in the yard. It also notes work on the problem in cognitive science, neuroethics, psychology, professional philosophy, urban legend, and autonomous car design.

Reading notes

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• The problem was introduced by Philippa Foot and later analyzed by Judith Thomson, Peter Unger, and Frances Kamm.
• One view says switching to the track with one person is obligatory because it saves five lives.
• Another view says diverting the trolley makes one partly responsible for the death, while doing nothing avoids that participation.
• The fat man case changes the setup by requiring you to push a man off a bridge to stop the trolley.
• A common distinction is that in the first case the one person’s death is a side effect, while in the second it is part of the plan.
• The doctrine of double effect is presented as a way to allow bad side effects while forbidding deliberate harm.
• The loop variant adds a track that rejoins the main line and raises the same question in a different form.
• Unger’s man in the yard case is used to argue that responses to trolley cases depend partly on psychology.
• In cognitive science, Hauser, Mikhail, and others treated the problem as evidence for an unconscious moral grammar.
• In neuroethics, Greene and Cohen used fMRI to compare emotional and cognitive responses to trolley cases.
• Surveys reported that about 90% of respondents choose to kill the one and save the five.
• A 2009 survey of professional philosophers found that 68% would switch, 8% would not switch, and 24% had another view or could not answer.
• The page says analogues of the trolley problem arise in autonomous cars when software must choose between harmful outcomes.