The trolley problem, introduced by Philippa Foot and later developed by Judith Jarvis Thomson, has occupied moral philosophers for decades as a paradigmatic test of ethical reasoning under impossible constraints. This paper argues that the trolley problem and all of its known variants are not genuinely unsolvable dilemmas but rather structures of unstated assumptions that dissolve upon systematic identification and exploitation of those assumptions. Four universal solutions are proposed — self-sacrifice, external obstruction, instrumental derailment, and upstream prevention — and their application is demonstrated across all major variants: the loop track, the footbridge, the fat villain, the transplant problem, the driver variant, numerical and demographic variants, the self-interest variant, and the autonomous vehicle variant. A fifth universal solution — direct neutralisation of the trolley itself — is identified as applicable across all variants. The paper argues that the number of solutions available to a rational agent is proportional to the number of unstated assumptions in the problem, and that retroactive introduction of new constraints absent from the original formulation constitutes a change of question rather than a rebuttal. The paper further argues that the purpose of the thought experiment is fully achieved and exceeded by this framework.
Chetan Raman (2026) studied this question.