If you replace every plank of a ship, is it still the same ship?

Plutarch recorded the puzzle two thousand years ago: Athenians preserved Theseus's ship by swapping out rotten planks until none of the original wood remained. Is it the same ship? Your body replaces most of its atoms over the years — so what, exactly, is 'you'?

— Plutarch, Life of Theseus (Parallel Lives) — c. 1st century AD — public domain
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