- At a metaphilosophical level, Ned Markosian — in "Identifying the Problem of Personal Identity" (chapter 6) — suggests that the standard way of putting the problem improperly biases the ensuing debate in favor of four-dimensionalism.
- Philosophers will often put the problem this way: under what conditions are person x at time t1 and person y at time t2 in fact the same person? But to what entities do the phrases 'person x at t1' and 'person y at t2' refer?
- Four-dimensionalists (perdurantists2) have a ready answer: to the temporal parts of person x and person y. Three-dimensionalists (endurantists3) have no truck with this — for they deny that persons have temporal parts. They prefer to ask after the conditions under which something that is a person at t1 is the same person as something that is a person at t2. But as we have seen, invoking sortal4 identity in order to state the problem incurs a heavy philosophical burden.
- Drawing on a new theory of property instantiations, Markosian proposes a new way of putting the problem that he claims levels the playing field for the 3Der and 4Der. Properties5, he notes, are often instantiated for extended periods of time: the sun has been hot for several billion years; leaves stay green in summer and turn red in the fall; the number seven has always been prime.
- Call these instantiations "episodes." Now we can ask some questions about whether this episode is the same as that. In particular, we can ask of persons. What are the conditions under which an instance of personhood at t2 is part of the same episode of personhood as an instance of personhood at t2?
- This characterization helps make sense of some of the vexing problems facing the 3Ders (e.g., the fission6 problem, the time travel7 problem, and the fetus8 / corpse9 problems). Though particularly welcome for the 3Der, success here should be regarded as good news all around, as it seems preferable not to presuppose one way of thinking about a problem by merely stating it (a theme Markosian sounds more than once in his chapter).
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