What is the trolley problem?
A runaway trolley is headed toward five people tied to the track. You can pull a lever to send it onto a side track, where it will kill one person instead. Most people say pull the lever. But in the footbridge version, the only way to stop the trolley is to push a large man off a bridge into its path—and most people refuse, even though the math is the same: one life for five.
Why do our answers change?
A utilitarian says save the five in both cases. A deontologist objects to using a person merely as a means, which pushing someone clearly does. The doctrine of double effect distinguishes harm you intend from harm you merely foresee. Today the puzzle has gone practical: engineers designing self-driving cars face versions of it, and MIT's Moral Machine experiment found that preferences vary across cultures.
FAQ
- Is there a right answer?
- Philosophers still disagree; the value is in exposing which principles our intuitions actually follow.
- Does this happen in real life?
- Similar trade-offs appear in triage, disaster response, and autonomous-vehicle programming.
Sources reviewed: 2026-10-25
References
- Foot, P. (1967). The problem of abortion and the doctrine of the double effect. Oxford Review, 5, 5–15.
- Thomson, J. J. (1985). The trolley problem. Yale Law Journal, 94(6), 1395–1415.
- Awad, E., et al. (2018). The Moral Machine experiment. Nature, 563, 59–64.