Trolley problem
Etymology
Devised by the British philosopher Philippa Foot in a 1967 essay on abortion and the doctrine of double effect, using a runaway tram. The American philosopher Judith Jarvis Thomson developed and named the "trolley problem" in the 1970s and 80s, adding the famous variant of pushing a large man off a footbridge. Once a specialist puzzle, it became a cultural shorthand for ethical dilemmas, revived by debates over how self-driving cars should behave in a crash.
noun phrase · /TROL-ee PROB-lum/
A thought experiment that pits the choice to let several people die against actively killing one to save them, testing our intuitions about right action.
What it names
The uncomfortable gap between doing harm and merely allowing it — and why numbers alone don’t settle what feels morally permissible.
Example
Programming the car’s crash response turned an abstract trolley problem into an engineering spec someone actually had to write.
Related idea
The veil of ignorance is a tool for designing just institutions; the trolley problem instead isolates a single agent’s choice in an unavoidable dilemma.