Philippa Foot Invented the Trolley Problem for a Different Argument

The trolley problem is universally cited as Philippa Foot's. It is. But she introduced it in 1967 as an example inside an essay about something else: 'The Problem of Abortion and the Doctrine of the Double Effect.'

Foot was trying to explain a puzzle about moral intuitions. We say it is wrong to kill one person to harvest their organs and save five. We also tend to say it is permissible to divert a runaway trolley from a track with five people on it to a track with one. Both are five-for-one trades. Why do they feel different?

Her answer was that the first involves using a person as a means — the doctor carries off the trade by doing something to the victim's body. The second involves redirecting an existing threat, and the harm to the lone bystander is a foreseeable side effect rather than the mechanism of rescue. This is the doctrine of double effect, a medieval Catholic moral principle Foot was rehabilitating for secular ethics.

The example took on a life of its own. Judith Jarvis Thomson added the footbridge variant in 1976 and continued to refine the cases for four more decades. Experimental psychologists from the 1990s onward turned the variants into an empirical tool for probing how humans actually decide moral trade-offs. Joshua Greene's 2001 fMRI study on trolley cases made them a staple of neuroscience.

None of this is what Foot wanted to do. She spent the rest of her career writing about virtue ethics and Aristotle. The trolley became a small industry without her — a strand of her thought that outgrew its author and took her name along for the ride.