The Trolley Problem Was Invented to Argue About Abortion

The version of the trolley problem most people meet is on the internet: a tram is bearing down on five workers, you are standing by a switch, do you divert it onto a track where it will kill one. The framing has lost almost all of the philosophical work the original was doing.

Philippa Foot, an Oxford moral philosopher, introduced the case in 1967, in an essay titled "The Problem of Abortion and the Doctrine of the Double Effect." The piece is barely about runaway trams. It is about whether there is a morally relevant difference between intending harm and merely foreseeing it — the Doctrine of Double Effect, a principle traceable to Thomas Aquinas and central to Catholic moral theology.

Foot's interest was abortion. Specifically: a craniotomy performed to save the mother's life, which the doctrine would forbid because the foetus's death is a means to the rescue, versus a hysterectomy on a cancerous uterus, where the foetus's death is foreseen but not intended. She constructed the tram case as a parallel: the driver who diverts the tram foresees the death of the one but does not intend it as the means.

The label "trolley problem" came nine years later. Judith Jarvis Thomson, at MIT, used it in her 1976 paper "Killing, Letting Die, and the Trolley Problem," then in 1985 added the footbridge variant — pushing a large stranger onto the tracks to stop the trolley — which most respondents reject even when the numbers are identical.

Foot herself was sceptical of the puzzle's later career. The point of the example, she wrote, was to embarrass the doctrine, not to settle ethics by majority vote.