Identity and philosophy · experts disagree
The ship of Theseus
Plutarch, Life of Theseus (about AD 100); the rebuilt-ship twist is Thomas Hobbes's, in De Corpore (1655).
The Athenians kept the ship in which Theseus sailed home from Crete, and as its planks rotted they replaced them one at a time with new ones. After enough years not a single original plank remained. Plutarch reports that philosophers already disagreed about whether it was the same ship. Hobbes added a twist. Suppose someone collected every plank as it was removed and, once all were out, assembled them into a ship in the original arrangement. Now there are two ships: the one in the harbour with all new planks, and the one in the warehouse made of all the old ones.
Which of them, if either, is the ship of Theseus?