 The Ship of Theseus Puzzle. The ancient historian Plutarch recounts the story of the famous ship of Theseus, whose parts were all gradually replaced as they wore down. The resulting ship was eventually displayed in Athens, where philosophers debated whether it was still the original ship of Theseus, despite having none of the original parts. In the modern era, Thomas Hobbes added a further twist to the story. Suppose that a custodian collected the original planks as they were removed from the ship and later put them back together in the original arrangement. In this version of the story, we are left with two seafaring vessels, one on display in Athens and one in the possession of the custodian. But where is the original Ship of Theseus? Some will say that the ship is with the museum, since ships can survive the complete replacement of parts (provided, at least, that the change is sufficiently gradual). Others will say that the ship is with the custodian, since ships can survive being disassembled and reassembled. Both answers seems correct, but this means that, at the end of the story, the ship of Theseus is in two places at once. More generally, the argument suggests that it is possible for one material object to exist in two places at the same time. We get an equally implausible result by working backwards. After all, there are clearly two ships at the end of the story, but both ships were also around at the beginning, for the reasons just given. So, at the beginning of the story, there were two ships of Theseus occupying the same place at the same time—one of which would go on to the museum and one of which would end up with the custodian.