Almost every one of these works the same way. It sets up two cases that seem relevantly similar, elicits opposite reactions to them, and then asks you to explain the difference. If you cannot, one of your reactions has to go — and which one you surrender tends to reveal what you were really committed to.
The trolley problemDivert a runaway trolley to kill one instead of five? Most say yes. Push a large man off a bridge to the same effect? Most say no. Testing: whether consequences alone determine rightness.
Mary's RoomA scientist knows every physical fact about colour but has only seen black and white. She leaves the room. Does she learn something new? Testing: whether physical facts exhaust all facts.
The ship of TheseusReplace every plank one by one. Same ship? Now rebuild the originals into a second ship. Which is it? Testing: what identity through change consists in.
The experience machineA machine gives you any experience you want, indistinguishable from reality. Would you plug in permanently? Testing: whether pleasure is all that matters.
The veil of ignoranceDesign society's rules without knowing who you'll be in it. Testing: what principles impartiality actually generates.
Philosophical zombiesA being physically identical to you with no inner experience. Conceivable? Testing: whether consciousness is identical to physical structure.
The Chinese RoomFollow a rulebook to produce fluent Chinese you don't understand. Testing: whether symbol manipulation can ever constitute understanding.
The prince and the cobblerA prince's consciousness wakes in a cobbler's body. Who is that? Testing: whether identity follows the body or the mind.
The myth of SisyphusCondemned to roll a boulder uphill forever. Camus asks us to imagine him happy. Testing: whether meaning requires a point.
The evil demonSuppose a powerful deceiver manipulates every perception you have. What survives the doubt? Testing: what can be known with certainty.
The brain in a vatThe modern demon: a brain stimulated to produce exactly your experiences. Testing: whether you can rule out radical scepticism.
The Turing testA machine converses indistinguishably from a person. Does it think? Testing: whether behaviour can settle questions about minds.
An argument wearing a story.What a thought experiment is
The objectionDo these actually work?
They have serious critics, and the criticisms are worth taking as seriously as the experiments. The first is that intuitions about bizarre scenarios may simply be unreliable — our moral responses evolved for ordinary situations, and there is no obvious reason they should track truth in cases involving footbridges or teleporters. The second is that stripping away context can remove exactly what mattered: real moral situations involve relationships, uncertainty, and history, all of which these scenarios delete by design.
Empirical work has sharpened the worry. Responses to trolley cases vary with how the scenario is worded and the order in which cases are presented, which is uncomfortable if the reactions are supposed to be evidence about moral reality rather than about framing. A reasonable position is that thought experiments are excellent at exposing inconsistency in what we already believe, and much weaker as direct evidence for what is true — which is still a substantial thing for an argument to do.
People also askQuick answers
What is a thought experiment in philosophy?
An imagined scenario designed to isolate a single philosophical question by stripping away everything incidental, then test what our reaction to it reveals about our actual commitments.
What is the most famous philosophical thought experiment?
The trolley problem is the best known. It asks whether you'd divert a runaway trolley to kill one person instead of five, then varies the case to test whether consequences alone determine rightness.
Why do philosophers use thought experiments?
Because some questions can't be settled empirically. A thought experiment isolates one variable so it can be examined alone, and typically works by producing two reactions that can't both be right — forcing you to give something up.
Are thought experiments reliable?
Contested. Critics argue intuitions about bizarre scenarios may not track truth, and that stripping away context removes what matters. Responses to trolley cases also vary with wording and order, which is awkward if they're meant as evidence.