The Ship of Theseus: which one is the original?
Every part of the ship has been replaced. Is it still the same one? Take a position before the museum attendant shows you what has been kept.
The museum opens tomorrow
Imagine this scene. A ship waits beside a museum quay. You are preparing its sign. In your hand is a label reading “The Ship of Theseus — original”.
This ship, call it A, has kept its name, route and appearance. Over years of repairs, every part has been replaced. None of the initial ship’s material remains. Yet each repair was made to the ship then in service.
Here, “the same” means one object persisting through time: numerical identity. Two objects can look perfectly alike without being one and the same object. The question is not about the ship’s beauty or value.
Your first decision
Choose an initial reason, then respond to its objection. There is no score: each final position explains what it accounts for and what it asks you to accept.
Does the label still fit?
The museum attendant hands you some tape. Does the label “original” still belong on A? Choose the reason you find most convincing.
Is history enough when all the wood has changed?
The attendant shows you B: all the removed parts, kept and still usable, reassembled in their initial arrangement. This second ship floats beside A. They look exactly alike.
They point to an old plank in B’s hull: “This made those first voyages. Nothing now floating in A was there.”
Your reason can still hold: a sequence of repairs connects A to the initial ship. It does not depend simply on the name or route, which a replica could take over. But it does require accepting that the same object can lose every bit of its original material.
Where was the ship while its parts were in storage?
The attendant shows you B: all the removed parts, kept and still usable, reassembled in their initial arrangement. This second ship floats beside A. They look exactly alike.
They show you a photograph: for years, these parts lay separately in a warehouse. Meanwhile, A kept sailing.
Calling B the same ship means accepting that an object can survive dismantling, or disappear and return when reassembled. The parts alone, thrown in a heap, would not make a ship: their restored arrangement matters too. Can that interruption fit your idea of the same object?
Two labels do not make one object
The attendant shows you B: all the removed parts, kept and still usable, reassembled in their initial arrangement. This second ship floats beside A. They look exactly alike.
Should both get the label? A could sail away while B stays at the quay: they are two distinct objects.
If A is numerically identical to the initial ship, and B is too, then A and B should be one and the same object. Their resemblance does not solve that problem. Neither would giving them the same name. You can call both “heirs to the original”, but that is a different claim.
Your sign: A, the ship that carried on
You put continuity through change ahead of keeping the parts. A remains the initial ship; B is a reconstruction made from historically valuable material.
The strength of this position: an ordinary repair does not automatically create a new object. Its difficulty: how much continuity is enough? If everything were replaced in a single operation, would your answer change? That extra case does not settle the one at the quay; it asks you to make your rule more precise.
Your sign: B, the ship recovered
You give priority to the original parts, put together in their initial arrangement. B recovers the ship’s identity; A continued its use.
The strength of this position: it distinguishes authentic material from a perfect copy. Its cost: it accepts an object’s history spanning a period when its parts were scattered. It must also explain what A was during the repairs. At which replacement would it have stopped being the initial ship? Your label does not yet mark that boundary.
Your sign: two heirs, neither the original
You require both original material and a continuous history as an assembled ship. A lacks the first; B lacks the second. You put the label away: each preserves something of the old ship, but neither meets your rule.
This position does not merely say “I don’t know”. It sets a demanding criterion. Its cost appears immediately: if every bit of original material is essential, even a small repair threatens identity. To allow some replacements, you will need to explain which ones and why.
An old question, then a second ship
In Life of Theseus, chapter 23, Plutarch reports that the Athenians preserved the ship by replacing its worn timbers. Philosophers used it to debate whether it remained the same or not. That passage does not present a second reassembled ship.
In De Corpore, II, 11, § 7, Hobbes adds the possibility of collecting the old planks and reassembling them in their original order. This exposes the difficulty of calling two distinct ships numerically identical to the initial ship. Hobbes also proposes his own account: he distinguishes what is being identified and ties a ship’s identity to its matter. Our museum and its signs are an original staging of these questions, not a historical account.
The next thing you repair
Think of a familiar bicycle. Its tyres are replaced, then its chain, then its frame. Without looking back at your choice, could you finish this sentence: “It’s still my bicycle because…”?
Now test your reason with a second bicycle assembled from the old parts. You need not apply the same rule to it as to a ship, but explain why your rule changes. The useful question is not just “which one?” but “what am I trying to preserve when I say the same?”