- Not so long ago it was widely regarded as self-evident that statements of identity may be (on occasion, are) contingently true1. The burden of proof was then on opponents of contingent identity. Today the situation has altered dramatically. Compelling arguments against contingent identity seem to have shifted the burden to champions of contingency. To some observers of the scene the weight looks too heavy to bear.
- But this view of the matter is not uncontested. Recently an interesting case in behalf of contingent identity was developed by Allen Gibbard2. Gibbard's argument for contingency rests upon two metaphysical (or logico-metaphysical) principles that are widely rejected.
- One of these assumptions is that ordinary physical objects are four-dimensional entities that are composed of temporal parts or segments.
- The other is that statements of identity across possible worlds (transworld identity statements) are sortal-relative3.
- One may ask whether this metaphysical baggage is necessary for developing a case for contingent identity. One of the points I shall try to establish is that contingent identity is much more closely tied to the relativity thesis than is generally recognized.
- The point holds both for a 'multi-world' version of contingency and for a 'temporal' (one world) version of contingency. As Gibbard correctly suggests the former rests squarely upon the thesis that transworld statements of identity are sortal-relative4; as we shall see, the case for temporal contingency rests upon the thesis that diachronic (or 'transtemporal') identity statements are sortal-relative5. Contingency theorists are not committed to denying that there are 'favored' transworld or transtemporal heir lines6. They are committed to claiming that transtemporal and/or transworld heir lines are sortal-relative7.
- There is no reason to think that the case for contingency must rest upon the assumption that ordinary objects are temporal worms. But as we shall see, there is reason to doubt that advocates of a 'temporal worm' metaphysics are in a position to reject a 'multi-world' version of contingency. Since I believe (and argue below) that one cannot even begin to make a case for contingent identity without assuming some version of the Geachean thesis that identity is sortal-relative8, I doubt that temporal worm theorists are in a position to reject the relativity thesis.
- There are impressive arguments against relative identity9. My suspicion is that we have reason to reject a temporal worm approach to commonplace objects, if these arguments are sound. Of course this can be turned around. There are subtle arguments for saying that in the end we will have to learn to live with temporal worms10. If these arguments are sound, it may turn out that we will have to learn to live with the idea that identity is sortal-relative11.
Footnote 1: Cf. David Wiggins's claim that "...there undoubtedly exist contingent identity statements. 'Identity statements', in: Analytical Philosophy, second series, ed. by R. J. Butler (Oxford, 1965), pp. 40-7.
Footnote 2: Footnote 6: See David Kaplan's 'Transworld heir lines', in The Possible and the Actual, ed. by Michael J. Loux (Cornell, 1979), pp. 94-95.
Footnote 9: For a start, see Footnote 10: See "Cartwright (Richard) - Scattered Objects" (1975).
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