A famous old argument reveals something important about the identity of the ship through time. Suppose a ship (call it “Theseus 1”) was constituted by a certain collection of parts at a certain time long ago. Suppose the parts in that collection were gradually replaced by newer parts. Eventually we find ourselves with a ship (“Theseus 2”) that is the result of all this gradual replacement. It is the apparent “ descendant ” of Theseus 1. Suppose, however, that the cast-off parts were all saved and eventually were reassembled so as to constitute a ship (call it “Theseus 3”). Suppose Theseus 3 contains all and only the parts that constituted the original ship Theseus 1 at the outset. Since Theseus 3 is part-for-part indiscernible from Theseus 1, there is an inclination to identify Theseus 3 with Theseus 1. But since Theseus 2 emerged from Theseus 1 by a series of individually minor replacements, there is also an inclination to identify Theseus 2 with Theseus 1. We cannot consistently give in to both of these inclinations since it is obvious that Theseus 2 is distinct from Theseus 3. Chisholm suggests that the facts in the world leave this somewhat indeterminate. If a case like this were to arise in the real world, we would leave it to the courts to make a determination of which ship is the legitimate successor to the original. If the courts decide that Theseus 2 is the “real” descendant of Theseus 1, then we will have to accept this conclusion for all practical purposes.