J ens J ohansson How does the cohabitation approach reconcile the psychological-continuity view with the thesis that identity is what matters in survival? The idea is easiest to explain from the perspective of “four-dimensionalism”: the general account of persistence espoused by virtually all cohabitation theorists According to fourdimensionalism, things persist by having temporal parts, or “stages,” located at different times; the persisting object itself is a space-time “worm,” composed of its various stages.10 Conjoined with the psychological-continuity view, this theory yields that two stages belong to the same person in virtue of being related by psychological continuity In ordinary cases, of course, no stage belongs to more than one person In the fission case, however, Lefty and Righty share the same pre-fission stages (though no post-fission stages) Now consider such a shared pre-fission stage S1, a post-fission stage S2 of Lefty, and a post-fission stage S3 of Righty The relation between S1 and S2 seems to contain what matters, and so does the relation between S1 and S3 Crucially, in each of these cases, there is also a single person of which the relevant stages are parts: both S1 and S2 are parts of Lefty, and both S1 and S3 are parts of Righty It is not the case, then, that we have what matters between two stages in the absence of personal identity over time It has been protested, however, that while this approach accommodates some ideas in the vicinity of the intuition that personal identity is what matters, it does not accommodate that intuition itself (Parfit 1976; Sider 1996; 2001, 202–203) For instance, perhaps it accommodates the thesis that, for stages, belonging to the same person is what matters Moreover, perhaps it accommodates the thesis that, if what matters obtains between a person, as he is at time t, and a person, as he is at time t*, then the former person exists at t* However, according to the critics, what the relevant intuition requires is that, if what matters obtains between a person, as he is at t, and a person, as he is at t*, then the former person is identical to the latter person And the fact remains that the relation between Lefty, as he is prior to fission, and Righty, as he is after fission, seems to contain what matters; and the fact remains that Lefty is not identical to Righty 7. The stage view A more recent proposal also deserves a mention here According to another version of four-dimensionalism, the “stage view” (Hawley 2001; Sider 1996; 2001), although there are all those temporally extended objects that the “worm” theorist identifies us with, these objects are not what we refer to with ordinary names and predicates (such as “Henry” and “person”) Instead, every ordinary object is an instantaneous stage: thus, you and I and other persons – as well as chairs, doghouses, etc – exist strictly speaking only for a moment The stage theorist does not thereby hold that I have never been asleep, or will never eat lunch Instead, she handles temporal predication analogously with how Lewis analyses modal predication (Lewis 1986) According to Lewis, claims about how I could have been should be understood in terms of properties of modal counterparts of me: individuals located in other possible worlds who are suitably 134