 However, on reflection, it may seem that this is too swift. If we suppose that any possible history for Russell is a possible spatiotemporal and causal extension of the state that he was actually in at some time in his existence, then perhaps we may appeal to the same continuities that ground his identity over time in the actual world in order to ground his identity across possible worlds (cf. Brody 1980, 114–115; 121). For example, perhaps to say that Russell could have been a playwright is to say that there was some time in his actual existence at which he could have become a playwright. If so, then perhaps we can hold that for a playwright in a possible world to be identical with Russell is for that playwright to have, in that world, a life that is, at some early stage, exactly the same as Russell’s actual life at some early stage, but which develops from that point, in the spatiotemporally and causally continuous fashion that is characteristic of the continued existence of a human being, into the career of a playwright rather than that of a philosopher. However, although such a conception may seem initially attractive, it runs into difficulties if it is intended to provide conditions that are genuinely both necessary and sufficient for the identity of individuals across possible worlds. These difficulties include the fact that it seems too much to demand that Russell have exactly the same early history (or origin) as his actual early history (or origin) in every possible world in which he exists. Yet if Russell’s early history could have been different in certain respects, we face the question: ‘In virtue of what is an individual in another possible world with a slightly different early history from Russell’s actual early history identical with Russell?’—a question of precisely the type that the provision of necessary and sufficient conditions for transworld identity was intended to answer. (For discussion of this ‘branching’ conception of possibilities, and its implications for questions of transworld identity and essential properties, see Brody 1980, Ch. 5; Mackie 1998; Mackie 2006, Chs 6–7; Coburn 1986, Section VI; McGinn 1976; Mackie 1974; Prior 1960.)