Identity, Persistence, and the Ship of Theseus Heraclitus’s “river fragments” raise puzzles about identity and persistence: under what conditions does an object persist through timeas one and the same object? If the world contains things which endure, and retain their identity in spite of undergoing alteration, then somehow those things must persistthrough changes. Heraclitus wonders whether one can step into the same river twice precisely because it continually undergoes changes. In particular, it changes compositionally. At any given time, it is made up of different component parts from the ones it was previously made up of. So, according to one interpretation, Heraclitus concludes that we do not have (numerically) the same river persisting from one moment to the next. Plato is probably the source of this “paradoxical” interpretation of Herclitus. According to Plato, Heraclitus maintains that nothing retains its identity for any time at all:
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