Judith Jarvis Thomson on the Trolley Problem

Quote

"The trolley problem is the problem of saying why it is that the driver of the runaway trolley may turn his trolley, though the bystander may not turn his."

— Judith Jarvis Thomson, The Trolley Problem, Yale Law Journal (1985)

Historical Context

Judith Jarvis Thomson gave the trolley problem its name. In her 1976 paper "Killing, Letting Die, and the Trolley Problem," she took up the runaway tram example that Philippa Foot had introduced in 1967 and subjected it to relentless analysis. By 1985, in "The Trolley Problem," published in the Yale Law Journal, the problem had grown into a research program. Thomson's distinctive contribution was to see that the interesting version of the case is not the one Foot had emphasized. Foot had imagined the driver of the tram, who must choose between killing five and killing one. But the driver is in a special position: the tram is already under his control, and one of the two harms is, in a sense, unavoidable whatever he does. The genuinely puzzling case is the one Thomson invented — the bystander case, in which a person standing beside the track with a switch can divert the tram from five workers to one, without any prior responsibility for the situation.

The quote captures the problem in its canonical form: the driver may turn the trolley, but — on the traditional intuition — the bystander may not. Yet the actions seem morally identical: both involve redirecting a lethal threat from five people onto one. If the driver may turn, why may the bystander not? Thomson's own answer developed across the two papers. In "Killing, Letting Die, and the Trolley Problem" she argued that the difference lies in what the agent would be doing — the driver's turning is a redirection of a threat already under his control, while the bystander's turning would be imposing a new harm. But in "The Trolley Problem" (1985) she came to the opposite conclusion: the bystander may turn the trolley, and the problem of explaining why has no simple solution in the traditional categories of intention, duty, and double effect.

Philosophical Interpretation

The force of the quote lies in its demonstration that the trolley problem is a problem about moral principle, not about moral psychology. Both the driver and the bystander face the same arithmetic — five deaths or one — and both perform the same kind of action, the redirection of a moving vehicle. The difference between them must therefore be located in some feature of their situations: the driver's control over the threat, the bystander's neutrality, the distinction between what we do and what we allow. Thomson's formulation makes the problem precise because it shows that the easy answers fail. It cannot be that consequences alone matter, since then both may turn. It cannot be the doctrine of double effect, since neither agent intends the death of the one — both intend only to save the five, with the single death foreseen but not intended. Something else must be doing the work.

Thomson's own route ran through the language of rights. In the bystander case, she argued, the one person has no right that the bystander not turn the trolley — the bystander is not the author of the threat, and turning the trolley does not violate a claim of the person who dies, any more than the driver's turning does. On this analysis, the trolley problem dissolves into a question about the structure of rights and harms: when may we redirect a threat that is already under way, even at the cost of someone's life? Her conclusion — that the bystander may turn — was deliberately counterintuitive, and it has shaped the entire subsequent debate. The literature that followed, from the "loop variant" cases to the empirical trolley experiments of Joshua Greene and his colleagues, is a direct response to the problem as Thomson stated it.

Related Concepts

The quote is the canonical statement of the trolley problem and the source of the bystander case. It engages the distinction between killing and letting die, the doctrine of double effect, and the question of rights — whether the one person has a right not to be made the means of saving others. The problem connects to moral responsibility, since the bystander's choice determines whether responsibility falls on the agent or on the situation. It is also the paradigm of a moral dilemma and the test case for every normative theory, from consequentialism to deontology to virtue ethics.

Learning Path

Begin with the site's answer on what the trolley problem is, then the companion page on Philippa Foot's founding example. Read the site's answer on moral responsibility to connect the bystander case to the metaphysics of agency and control. To follow the modern debate, explore the psychology of moral judgment in trolley experiments and the applied use of trolley-style reasoning in the ethics of self-driving cars, where the choice between harms has moved from thought experiment to programming problem. Finally, test Thomson's rights-based analysis against the deontological tradition in Kant's Groundwork of the Metaphysics of Morals.