Philippa Foot and the Trolley Problem

Quote

"To make this parallel as close as possible it may rather be supposed that he is the driver of a runaway tram which he can only steer from one narrow track on to another; five men are working on one track and one man on the other; anyone on the track he enters is bound to be killed."

— Philippa Foot, The Problem of Abortion and the Doctrine of the Double Effect (1967)

Historical Context

The passage comes from "The Problem of Abortion and the Doctrine of the Double Effect," published in the Oxford Review in 1967. Foot's essay was written as an intervention in the debate over abortion, which had been inflamed by the thalidomide scandal and the case of the mother of four who had contracted rubella, and which was pressing on the law in Britain and the United States. Catholic moral theology had traditionally defended the position that abortion could sometimes be permitted under the doctrine of double effect: an action with two effects, one good and one bad, may be performed if the bad effect is merely foreseen rather than intended. Foot wanted to test that doctrine, and to do so she constructed pairs of cases designed to isolate the moral significance of intention, agency, and the distinction between doing harm and allowing harm.

The tram example in the quoted passage is introduced as a parallel to one of her original cases, the "transplant case," in which a surgeon is imagined able to save five dying patients by cutting up one healthy man and distributing his organs. Foot's innovation was to transpose the dilemma onto a runaway tram, which could be steered so as to kill one worker rather than five. It was this example — later dubbed the "trolley problem" by Judith Jarvis Thomson — that captured the philosophical imagination. Foot's essay is now regarded as the founding document of the entire literature on the trolley problem, and it remains the reference point for debates in ethics, psychology, and the ethics of artificial intelligence.

Philosophical Interpretation

The tram case is designed to make a precise point. The driver of the tram faces a forced choice: he may do nothing, and five men die, or he may steer onto the other track, and one man dies. Foot's aim in introducing the example was to probe the distinction between what an agent directly does and what the agent merely foresees, and the related distinction between killing and letting die. Her own analysis appealed to the asymmetry between positive duties — duties to help — and negative duties — duties not to harm. In the transplant case, the surgeon would have to kill the healthy man, violating the stringent negative duty not to harm; in the tram case, the driver's choice between two harms has a different structure, because whatever he does, he is not introducing a new harm but choosing between courses of action that both involve death.

The example is so powerful because it forces the question: what morally distinguishes the two cases? If consequences are all that matter, both choices are equivalent — one death versus five. If intention matters, the doctrine of double effect must explain why foreseen but unintended harm can sometimes be permitted while intended harm cannot. Foot's own answer — that negative duties are more stringent than positive duties, so that it is worse to kill than to allow to die — generated an enormous literature. Thomson's subsequent work on the same problem showed that the driver's case is actually easier than the "bystander" variant she invented, in which a stranger can divert the tram by throwing a switch; and it is the bystander case, not the driver case, that has become the standard formulation. The trolley problem remains unsolved in the sense that no principle has won general acceptance — which is precisely what makes it a permanent laboratory for moral theory.

Related Concepts

The passage introduces the trolley problem as a test case for the doctrine of double effect, which distinguishes intended from merely foreseen consequences. It trades on the distinction between killing and letting die, and on the contrast between positive and negative duties. The example also raises the difference between doing and allowing harm, which structures debates about euthanasia, famine relief, and war. The cases belong to the wider family of moral dilemmas, situations in which every available course of action seems to involve wrongdoing, and they bear directly on moral responsibility: what is the agent accountable for when the choice is forced?

Learning Path

Start with the site's answer on what the trolley problem is, which maps the standard cases. Then read the site's answer on moral responsibility to see how the dilemma connects to questions of agency and accountability. For the philosophical context, explore the doctrine of double effect and its critics. Continue with Judith Jarvis Thomson's reformulation of the problem in the companion quote page, then test the principles against applied debates in the ethics of self-driving cars and autonomous weapons, where the trolley problem has moved from thought experiment to engineering question.