The Trolley Problem
A runaway trolley is headed toward five people tied to the tracks. You can pull a lever to divert it to a side track, where only one person is tied. Do you pull the lever?
Introduced by philosopher Philippa Foot in 1967 and later refined by Judith Jarvis Thomson, the Trolley Problem is the classic test case for utilitarian ethics. It forces a direct confrontation: is causing one death to prevent five deaths morally the same as simply allowing five deaths to happen?
Foot, P. (1967). The Problem of Abortion and the Doctrine of Double Effect. Oxford Review, 5, 5–15.
What's actually being tested
Most people say they'd pull the lever. Five lives outweigh one. The math seems obvious. But Judith Jarvis Thomson introduced a variation: instead of a lever, you're on a bridge above the tracks. The only way to stop the trolley is to push a large stranger off the bridge onto the tracks, using his body as a brake. Same arithmetic (one dies, five are saved), but now almost nobody says they'd do it.
The Trolley Problem isolates this discomfort. Our moral intuitions aren't simply utilitarian. We treat actively harming someone differently from redirecting harm, even when the outcomes are identical.