menu

Thinkers

Judith Jarvis Thomson

Analytic · North America · 1929 to 2020

American philosopher known for the switch and footbridge cases, which ask why two cases with the same numbers feel so different.

What it is

Judith Jarvis Thomson (1929 to 2020) was an American philosopher who worked in ethics and metaphysics. She is best known for her work on the trolley problem, a puzzle about when it is right to cause one death to prevent several, and for an article on abortion that has been widely discussed.

She was born in New York City. She took a degree in philosophy at Barnard College in 1950, then a second degree at Newnham College, Cambridge, in 1952 and a master's degree there in 1956. She earned her doctorate at Columbia University in 1959. She taught for a year at Boston University and from 1964 at the Massachusetts Institute of Technology, where she spent most of her career.

The main ideas

  • The trolley problem. The puzzle was first posed by the British philosopher Philippa Foot, in a case where a runaway tram can be steered from a track with five workers onto a track with one. Thomson took it up and developed it in two articles, in 1976 and 1985.
  • The switch. In her version a bystander stands near a switch that could send the trolley onto the track with one worker. It is widely thought permissible to throw it.
  • The bridge. In another version a bystander on a footbridge could stop the trolley by pushing a heavy man onto the track. It is widely thought wrong, though the numbers are the same: one life lost, five saved.
  • Why the difference. It is a puzzle why the two cases feel so different when the numbers are the same. Her variants seem to undermine Foot's explanation based on duties, and different thinkers explain the difference in different ways.
  • Against simple theories. Cases like these are hard for conventional theories to predict, such as consequentialism, which looks only at results, and Thomson herself was opposed to consequentialist views.
  • The violinist. In her 1971 article "A Defense of Abortion" she described a famous violinist who needs a stranger's kidneys for nine months, to test whether a right to life settles the question of abortion.

What it looks like in practice

Imagine a doctor who could save five patients by sacrificing one healthy visitor. Most people recoil, although they would accept switching a runaway trolley to spare five. Thomson's cases are built to let a person test such reactions one at a time, changing a single detail and noticing whether the answer changes. This is an illustration of her method, not an example from her writing.

Books and moments

  • A Defense of Abortion (1971) introduced a thought experiment for which she is especially well known.
  • Killing, Letting Die, and the Trolley Problem (1976) and The Trolley Problem (1985) set out her variants of Foot's case.
  • MIT was her academic home from 1964, and she remained there for most of her career.

Questions and criticism

  • Intuitions as evidence. It is fair to ask how much weight the common reactions to made-up cases should carry in an argument about what is right.
  • What separates the cases. The pair of cases does not settle by itself what the difference is between throwing a switch and pushing a man, and thinkers have offered different answers.
  • Unreal cases. It is also fair to ask what stories about runaway trolleys teach about real choices.

Close neighbours

The page on Philippa Foot is the closest, since Thomson took her case and reworked it. The pages on Jeremy Bentham and John Stuart Mill present the consequentialist outlook that cases like these put under strain, and the page on Immanuel Kant presents a duty-based tradition.

Written by epchē in our own words, and checked against independent sources on 29 October 2026. The sources are listed below.

Who they connect to

Influenced by

  • Philippa Foot · She named and carried on the trolley puzzle that Foot had first set out.

Other Analytic thinkers

Sources we used

See where you stand Find them on the map

Something wrong or missing on this page? Tell us.