 This second point is an extension of the observation that, if (as most philosophers believe) Bertrand Russell has some essential properties (properties that he has in all possible worlds in which he exists), to stipulate that one is talking about a possible world in which Russell is a playwright is, at least implicitly, to stipulate that the possible world is one in which someone with Russell’s essential properties is a playwright. For example, according to Kripke’s ‘necessity of origin’ thesis, human beings have their parents essentially (Kripke 1980). If this is correct, then, when we say ‘There is a possible world in which Russell is a playwright’, it seems that, if our stipulation is to be coherent, we must be at least implicitly stipulating that the possible world is one in which someone with Russell’s actual parents is a playwright, even if the identity of Russell’s parents is unknown to us, and even though we are (obviously) in no position to conduct an empirical investigation into the ancestry, in the possible world, of the individuals who exist there. Thus, it seems, even if Kripke is right in insisting that we need not be able to specify non-trivial necessary and sufficient conditions for being Russell in another possible world if we are legitimately to claim that there are possible worlds in which he is a playwright, it might nevertheless be the case that there are such necessary and sufficient conditions (cf. Kripke 1980, 46–47 and 18, note 17; Lewis 1986, 222).