Philippa Foot Invented the Trolley Problem to Argue About Abortion

Philippa Foot was an Oxford philosopher trying to settle a narrow disagreement when she sketched the runaway tram in 1967. Her paper, The Problem of Abortion and the Doctrine of the Double Effect, asked why we feel free to redirect a runaway tram onto a track where it will kill one workman, but feel queasy about a surgeon killing one healthy patient to harvest organs that would save five. Both involve trading one life for five.

Foot's answer leaned on the difference between doing harm and allowing harm, between what you intend and what you merely foresee. The trolley case was a side example, not the headline.

Judith Jarvis Thomson took the case seriously a decade later and built it into a small industry. Her 1985 paper introduced the footbridge variant: same five workmen, same runaway tram, but now your only way to stop it is to push a large stranger off an overpass into its path. Most people who happily flip the switch refuse to push the stranger, even though the math is identical.

That asymmetry is what the problem actually probes. People do not reason about ethics by adding up lives. They use a tangle of rules — about touching, about using a person as a means, about who is already in the path of harm — that consequentialist arithmetic ignores.

The self-driving car industry briefly tried to recruit the trolley problem as a real engineering question. It is a poor fit. Real autonomous systems do not face neat one-versus-five tradeoffs; they face physics, sensor noise, and probability distributions. The thought experiment was always meant to expose how human judgment works, not to write code.