Abstract
Four-dimensionalists offer a unified picture of various puzzles about identity over time, including the puzzle of fission, the puzzle of constitution and the puzzle of undetached parts. What unifies the four-dimensionalist approaches to these puzzles is the possibility of temporal overlap—the possibility for distinct continuants to share a common temporal part, or stage. I claim that the unified picture is inconsistent, if there are informative criteria of identity over time. I will show that while temporal overlap is compatible with four-dimensionalist criteria of diachronic composition, temporal overlap is incompatible with any four-dimensionalist criteria of diachronic identity.
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Notes
See Sider (2001, pp. 152–153).
See Parfit (1984, pp. 254–255).
See Lewis (1983, pp. 61–63).
See Sider (2001, pp. 5–6).
See Lewis (1986, pp. 192–193).
Recent skeptics, such as Trenton Merricks (1998), raise doubts about the purpose of criteria of diachronic identity. As should be apparent from the remarks above, I think that the skeptical challenge can be resisted. But this paper is not the place for a detailed stand on this issue.
Eric Olson draws the distinction between the unrestricted, or `broad’, criterion and the restricted, or `narrow’, criterion in (1997, pp. 25–26). He adds, though, that if the concept of a person is a substance concept—that if something is a person at one time, then it is a person throughout its life—then the restricted criterion is equivalent to the unrestricted one, for the substitution of `K’ by `person’. This is incorrect. For even on the mentioned assumption, the restricted criterion does not cover all questions of diachronic identity and distinctness about persons, whereas the unrestricted criterion does. The moral is that the question of whether the concept of a person is a substance concept is independent of the question of the scope of a criterion of personal identity.
See Lewis (1983, p. 59).
Lewis (1983, pp. 58–59).
Lewis (1983, p. 61).
See Perry (1975, pp. 8–9) for a similar confusion.
It is worth pointing out that changing the left-hand side of (C2) to `necessarily, there is a unique continuant of kind K of whom S1 and S2 are stages’ immediately rules out temporal overlap of distinct things belonging to the same kind, but still allows temporal overlap of distinct things belonging to different kinds. However, changing the left-hand side of (C3) to ‘necessarily, there is a unique continuant of kind K composed of stages S1, S2, ..., Sn’ does not rule out temporal overlap of distinct things belonging to the same kind. In fact, this strengthened version of (C3), incorporating a uniqueness claim, belongs to the inventory of standard four-dimensionalism.
Temporally insensitive criteria of kind-membership are usually construed as modally insensitive as well: a continuant x belongs to kind K iff x has certain K-determining properties at all times and all possible worlds at which it exists.
I am grateful to Cody Gilmore and an anonymous referee for pushing this space-time analogy.
Given our considerations in previous sections, if co-location by temporal overlap is possible, then cross-temporal facts about particular continuants remain untrackable. Moreover, if co-location by temporal overlap is possible, then cross-temporal facts are the only facts that can be appealed to in distinguishing the continuants at the time of co-location. Since cross-temporal facts are untrackable in the case of temporal overlap, facts of identity and distinctness at the same time are also untrackable in the case of temporal overlap.
Thanks to Cody Gilmore, Ted Sider and an anonymous referee for helpful criticism. Special thanks to Elizabeth Harman for her comments at the 2007 Central Division Meeting of the APA in Chicago.
References
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Sattig, T. Identity in 4D. Philos Stud 140, 179–195 (2008). https://doi.org/10.1007/s11098-007-9136-6
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DOI: https://doi.org/10.1007/s11098-007-9136-6