⛵ ≡ ?
The Ship of Theseus
Plutarch, Life of Theseus · c. 100 CE
The puzzle
The Athenians preserved Theseus’s ship by replacing rotting planks with new ones. After every plank had been replaced, was it still the same ship?
Note
Hobbes added the harder version: someone collects the discarded planks and rebuilds the original. Now there are two ships, each with a claim. The puzzle isn’t really about ships — it’s about what makes any persisting object (a city, a forest, a person) the same thing across time. Modern philosophers split into psychological-continuity, physical-continuity, narrative or social-recognition theories, and the four-dimensionalist view that the ship is a sum of temporal parts and the question dissolves. None of the answers feels obviously right when you try to apply it to yourself. The cells in your body have all turned over many times. So has the language you think in.