 First, Forbes (1987: 139ff) argues that the identification of possible worlds with constructions out of compossible states of affairs solves the problem of accidental intrinsics (Lewis 1986: 199–201). Let us consider an intrinsic property of a human being, say me, such as having two hands. I might have existed without having had two hands. On the concretist account this implies that there is a possible world in which I have a different number of hands. But how can one and the same individual have two as well as fewer/more hands “in different worlds”? If the worlds are mereological sums that have me as a common part, this seems not possible. Lewis concludes that the same object cannot be part of different possible worlds. An object can only be in different possible worlds by having counterparts in them.