ship of Theseus the ship of the Greek hero Theseus, which, according to Plutarch (‘Life of Theseus,’ 23), the Athenians preserved by gradually replacing its timbers. A classic debate ensued concerning identity over time. Suppose a ship’s timbers are replaced one by one over a period of time; at what point, if any, does it cease to be the same ship? What if the ship’s timbers, on removal, are used to build a new ship, identical in structure with the first: which ship has the best claim to be the original ship? See also IDENTITY, INDIVIDUATION , PERSONAL IDENTITY. W.J.P.