Puzzles about Identity and PersistenceThe puzzling doctrine for which Heraclitus is best known is reported by Plato (Cratylus402A): Heraclitus, you know, says that everything moves on and that nothing is at rest; and, comparing existing things to the flow of a river, he says that you could not step into the same river twice. Plutarch, no doubt following Plato, also ascribes this idea to Heraclitus (62=B91). The idea is this: since the composition of the river changes from one moment to the next, it is not the same (numerically the same) river for any length of time at all. Note that Plato thinks that Heraclitus uses the river as an exampleof what he takes to be a general condition: everythingis like a river in this respect. That is, nothingretains its identity for any time at all. That is: there are no persisting objects. Indeed, according to Aristotle, there was a follower of Heraclitus who carried it even further (Metaph.1010a7-15):
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