Killing, Letting Die, and the Trolley Problem by Judith Jarvis Thomson

Context

This work brings together the papers in which Judith Jarvis Thomson created the modern trolley problem literature. Its centerpiece is the 1976 essay "Killing, Letting Die, and the Trolley Problem," published in The Monist, which took Philippa Foot's 1967 trolley example and transformed it. Foot had used the trolley to explore the distinction between doing harm and allowing harm; Thomson added the fat man and the loop variants, showed that the doing/allowing distinction could not explain our judgments, and argued that the real structure is one of people's rights. The work also includes Thomson's influential treatments of the doctrine of double effect and of the moral significance of the distinction between killing and letting die. Written at the height of the revival of applied ethics, it is one of the most consequential bodies of work in twentieth-century moral philosophy.

Core Arguments

Thomson's central argument in "Killing, Letting Die, and the Trolley Problem" is that the intuitive difference between the switch case and the fat man case cannot be explained by the standard distinctions of the moral tradition. The doctrine of double effect says that harms intended as means are forbidden while harms foreseen as side effects may be permissible; Thomson argues that the loop variant destroys this explanation, because in the loop case the death is a means, yet people still approve the switch. She concludes that the explanatory work is done by rights: in the switch case the bystander does not violate anyone's rights by diverting a threat, while in the fat man case pushing the man violates his right not to be used as a means. The core argument is thus a defense of a rights-based, deontological structure against both utilitarian arithmetic and the classical doctrine of double effect.

A second line of argument concerns the distinction between killing and letting die. Foot and others had argued that the distinction is morally significant — that killing is harder to justify than letting die. Thomson examines cases in which the distinction appears to collapse and cases in which it appears decisive, and she concludes that the moral weight of the distinction depends on the structure of rights and on what each party is entitled to claim from the other. The work therefore does not simply defend one side of the classic debate; it dissolves the debate by showing that both sides were operating with too coarse a set of categories.

Key Concepts

The work's key concepts are the fat man variant, the loop variant, the distinction between doing and allowing, the doctrine of double effect, and the rights-based explanation of moral permissibility. Thomson's "Thomson's switch" — the claim that the bystander may divert the trolley — became a standard term, and her argument that the one on the track has a right not to be used as a means introduced a rights vocabulary that reshaped the debate. The work also develops the distinction between "distributive" and "redistributive" readings of the cases: whether the trolley's threat is merely redirected to the one person (permissible) or the one person's body is commandeered as a resource (forbidden). This distinction, which Thomson pressed against Foot's framework, remains central to the contemporary literature.

Legacy & Influence

Thomson's work generated the largest literature of any thought experiment in ethics. Her fat man and loop variants are used in philosophy courses worldwide, and her rights-based analysis is a principal alternative to the doctrine of double effect in explaining trolley intuitions. The empirical turn in moral psychology — the study of how people actually judge trolley cases, associated with Joshua Greene and others — grew directly out of Thomson's formulations. Her arguments also shaped the applied ethics of autonomous vehicles, whose crash algorithms must decide between "switch" and "push" solutions. In the philosophy of the doctrine of double effect, Thomson is the critic every defender must answer, and her case for the rights-based reading is one of the most influential defenses of deontology in the modern period.

Reading Guide

The core text, "Killing, Letting Die, and the Trolley Problem" (1976), should be read alongside Foot's original 1967 paper, "The Problem of Abortion and the Doctrine of the Double Effect," since Thomson's arguments are point-by-point replies. Readers should then turn to Thomson's later "The Trolley Problem" (1985), where she revises her earlier conclusions, and to her The Realm of Rights (1990), which contains the systematic rights theory. For the secondary literature, the Stanford Encyclopedia of Philosophy entry "The Trolley Problem" is the best starting point, followed by the collected volumes on the trolley problem in contemporary ethics. Note that although the 1976 article is the origin of this body of work, the material is also collected and republished in Thomson's essay volumes, including Rights, Restitution, and Risk (1986).

Related Works

• "The Problem of Abortion and the Doctrine of the Double Effect" by Philippa Foot (1967): the origin of the trolley problem.
• "The Trolley Problem" by Judith Jarvis Thomson (1985): Thomson's later revision of her own analysis.
• The Realm of Rights by Judith Jarvis Thomson (1990): the systematic rights theory.
• The work connects to the trolley problem, the fat man variant, the loop variant, and Thomson herself.