The Ship of Theseus
If you replace every plank of a ship one by one, is it still the same ship? And if someone builds a second ship from the old planks, which one is the original?
2 min read
According to Plutarch, the Athenians kept the ship of their legendary hero Theseus for centuries, replacing rotting planks with new timber. Philosophers argued about it: was it still Theseus’s ship?
In 1655, Thomas Hobbes made it harder. Suppose someone collected all the discarded planks and rebuilt the original ship from them. Now there are two ships. Which is the real one?
Possible answers
- Continuity: the ship that has been continuously sailed and repaired is the original.
- Material: the one made from the original planks is the original.
- Function and name: identity is a label we assign for practical purposes, and there is no deeper fact.
- Four-dimensional view: objects are stretched through time, so “the ship” is the whole history, not a snapshot.
Why it keeps coming back
- Your body replaces most of its cells over the years (though not all; many neurons last a lifetime).
- Bands with no original members still tour under the original name.
- A codebase rewritten line by line still ships under the same version history.
- Cities are rebuilt on the same sites for centuries.
The puzzle doesn’t have one correct answer. It shows that “same” has several meanings, and that many arguments are really disagreements about which one people mean.
“The ship wherein Theseus and the youth of Athens returned had thirty oars, and was preserved by the Athenians… they took away the old planks as they decayed, putting in new and stronger timber in their place.”
Bring it up
“If a band replaces every original member, is it still the same band? Philosophers have argued about a version of that for 2,000 years.”
Follow the thread
- RelatedChesterton’s fence: ask why it’s there before you tear it down Keeping or replacing old parts raises the question of what each one was doing.
- RelatedVenice stands on an upside-down forest Cities face the same puzzle: Venice has been rebuilt piece by piece on the same foundations for centuries.
