Would you divert a runaway trolley to kill one person instead of five?

Philippa Foot introduced the scenario in 1967 to probe the moral difference between killing and letting die: a runaway trolley will kill five people unless you pull a lever to divert it onto a side track, where it will kill one. Most people say pull the lever, yet balk at a structurally similar case where the one death requires directly pushing someone. The gap between the two intuitions became a central puzzle in moral philosophy.

— Philippa Foot, The Problem of Abortion and the Doctrine of Double Effect — Oxford Review, 1967