A thought experiment is an imagined scenario that is designed to help you think through a problem or idea. Philosophy is not the only discipline that uses them. Famous thought experiments in other disciplines include Schrodinger’s cat (quantum physics), Hilbert’s infinite hotel (mathematics), and the prisoner’s dilemma (game theory, economics). Thought experiments have even found their way into pop-culture; for example, Phillippa Foot’s trolley problem was featured in the sitcom, “The Good Place,” and Frank Jackson’s Mary’s room thought experiment is discussed in the film Ex Machina.

Thought experiments can be found in writings dated all the way back to the origin of philosophy in Ancient Greece. For example, in The Republic, Plato asks readers to imagine a ring, such as the one presented in the myth of Gyges, that makes you invisible, and poses the question: What would you do if you had such a ring? Would you break the law or do things normally considered bad, knowing you could get away with it? The point isn’t to plan for a time when you might actually get such a ring and whether such a ring could actually exist isn’t important. The point is to get you thinking about the nature of justice.

Thought experiments have sometimes been elaborated upon in fantasy (e.g., Gollum’s ring in The Hobbit and The Lord of the Rings trilogy)¹ and science fiction (e.g., Minority Report² and The Matrix³). Thought experiments have even been elaborated upon in more realistic fiction and films (e.g., Crimes and Misdemeanors and The Departed⁴). In each case, the story gives us something to think about with regard to the nature of things, such as justice, free will, or even reality itself.

^{1. This is perhaps the most famous allusion to the ring of Gyges.↩}

^{2. This film examines questions related to free will, determinism, and justice.↩}

^{3. This film raises questions concerning the difference between appearance and reality, an issue dating all the way back to Plato and treated in Descartes’ “evil genius” thought experiment. ↩}

^{4. Both films examine a question posed in Plato’s Republic related to the ring of Gyges: Isn’t it best to be a bad person who appears good and worst to be a good person who appears bad? Plato answers no. Still the challenge of how to address the question properly persists and is poignantly explored in both of these films. ↩}