 A wooden ship is constructed and christened ‘Theseus II’. As planks come loose over the years, they are discarded and replaced. After three hundred years, the last of the original planks is replaced. Call the resulting ship ‘the mended ship’. The descendants of the original owners have been collecting the discarded original planks, and—three hundred years after the christening—they obtain the last of them and construct a ship that is indistinguishable from the original. Call the resulting ship ‘the reconstructed ship’. Which, if either, of these two ships is identical to Theseus II? It is natural to suppose that there is no fact of the matter: it is indeterminate which of the two ships is Theseus II.