Theseus is famous in Greek mythology as the slayer of the Minotaur, a half-man, half-bull
monster who lived in the Labyrinth in the island of Crete. According to Plutarch, the ship in which Theseus
sailed back to Athens was preserved for many generations, its old planks being replaced by
new ones as they decayed.
Now suppose that a few hundred years later, all the original parts of the ship had been
replaced, one by one, so that none of the original ship remained. Is the preserved ship still
Theseus' ship? Or is it a copy? And if the latter, then at what point did it cease to be Theseus'
It seems that if just one plank were replaced, it would still be Theseus' ship. And if it was
still his ship, and another plank were replaced, then it should still be Theseus' ship. By this
reasoning (which is the same as in the sorites paradox), it would be Theseus' ship even after all
planks are replaced.
This problem is not merely another version of the sorites, however. It involves the notion of
identity, of what we mean by something being the "same" object. Suppose that we regard the final
ship as Theseus' ship. What if all the old planks, nails, etc., had been stored in a warehouse and
someone put them back together again. Would there then be two Theseus' ships?
Similar paradoxes of identity arise in certain science fiction scenarios and in connection
with the philosophy of mind. Suppose you are teleported by
having your body disintegrated in one place and reassembled in another from new materials. Are
you still "you"? Your body is made of different atoms, but it is still you as far as your mind is
concerned, right? But what if instead of having your original body disintegrated you merely
have a copy made? Then is the copy still you?
See also Sorites Paradox
©2000 Franz Kiekeben