Experiment
Which One Is the Ship?
Plutarch recorded the puzzle around 75 CE: the Athenians preserved Theseus's ship for centuries by replacing its rotting planks one at a time, until eventually none of the original wood was left. Was it still his ship? In 1655, Thomas Hobbes made the question sharper in De Corpore by adding a second ship: what if someone collected every discarded plank and quietly rebuilt the original out of them? Now there are two candidates for "the real ship," and picking one forces you to say, out loud, which kind of sameness actually mattered to you the whole time.
First, you'll watch a ship get rebuilt plank by plank and mark the point, if any, where it stops feeling like the same ship to you. Then a second ship enters the picture, and you'll decide which one actually deserves the name.
Drag the slider to replace planks, one at a time. Stop wherever you'd say it's no longer the same ship. If you don't think it ever stops being the same ship, drag all the way to 16 and confirm there.
While the repairs went on, a collector quietly saved every plank the Athenians pulled out and, working alone in a second harbor, reassembled them in their original order. By the time the repairs finished, all 16 original planks had been replaced in the harbor ship. There are now two ships.
Ship A
Docked in the original harbor. Repaired continuously, in the same slip, under the same name, sailed every season the whole time. Made entirely of new planks now.
Ship B
Assembled just now, in a second harbor, out of the 16 original planks, in their original order. Has never sailed. Was in storage the entire time the repairs were happening.
If only one of these can be the ship Theseus actually sailed, which is it?
Discussion
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