 But now consider a series of possible worlds, beginning with the actual world, each containing a bicycle just slightly different from the one in the previous world, the last world in the sequence being one in which there is a bicycle composed of completely different parts from the one in the actual world. One cannot say that each bicycle is identical with the one in the neighbouring world, but not identical with the corresponding bicycle in distant worlds, since identity is transitive. Hence it seems one must either adopt an extreme mereological essentialism, according to which no difference of parts is possible for an individual, or reject the interpretation of de re modal discourse as asserting identity across possible worlds.