The Ship of Theseus

Plutarch tells of the ship Theseus sailed home: the Athenians kept it for centuries, replacing each plank as it rotted. Suppose every original piece is gone at last. Is it still the same ship? Thomas Hobbes later added a twist: if the old planks are gathered into a second hull, which one has the better claim?

The paradox forces a choice about what “same” means: same materials, same continuous history, or same function. Different questions suit different choices. A restoration workshop, a court, and a person looking back at their own beliefs will not pick the same test, and they should say which one they use.

You are a slow ship. Beliefs get replaced plank by plank. A serious mind can say, “I changed my mind,” without pretending the earlier person was a stranger and without pretending nothing important changed.

The stored planks

A museum replaces every timber of a working replica over twenty years and stores the removed timber in a warehouse. A volunteer says the pile is the real ship, because authenticity means original parts. A sailor says the hull on the water is the real ship, because a ship is something that sails.

Both are choosing a definition. The careful next sentence names the definition instead of treating it as obvious.

Try this today Next time you argue about whether something is “still the same,” name the test you are using.