André Gallois (1998) attempts to defend the occasional identity thesis (OIT), the thesis that objects which are distinct at one time may nonetheless be identical at another time, in the face of two influential lines of argument against it. One argument involves Kripke’s (1971) notion of rigid designation and the other, Leibniz’s law (affirming the indiscernibility of identicals). It is reasonable for advocates of (OIT) to question the picture of rigid designation and the version of Leibniz’s law that these arguments (...) employ, but, the problem is, some form of rigidity is required for one to affirm the occasional identity of objects, and some (restricted) version of Leibniz’s law must be conceded if identity really is involved. Gallois accordingly recommends an account of rigidity and a version of Leibniz’s law to this end.1 We find Gallois’ proposals entirely inadequate to their task. We aim in this paper is to explicate and defend an alternative approach for occasional identity theorists. We do not seek to defend (OIT) per se; our aim, rather, is simply to show that the arguments from rigid designation and Leibniz’s law are inconclusive. Let’s begin with an outline of these arguments. (shrink)

Traditionally, this puzzle has been solved in various ways. Aristotle, for example, distinguished between “accidental” and “essential” changes. Accidental changes are ones that don't result in a change in an objects' identity after the change, such as when a house is painted, or one's hair turns gray, etc. Aristotle thought of these as changes in the accidental properties of a thing. Essential changes, by contrast, are those which don't preserve the identity of the object when it changes, such as when (...) a house burns to the ground and becomes ashes, or when someone dies. Armed with these distinctions, Aristotle would then say that, in the case of accidental changes, (1) and (2) are both false—a changing thing can really change one of its “accidental properties” and yet literally remain one and the same thing before and after the change. (shrink)

André Gallois’ (1993) modified account of restrictedly rigid designators (RRDs) does indeed block the objection I made to his original account (Gallois 1986; Ramachandran 1992). But, as I shall now show, there is a deeper problem with his approach which his modification does not shake off. The problem stems from the truth of the following compatibility claim: (CC) A term’s restrictedly rigidly designating (RR-designating) an object x is compatible with it designating an object y in a world W where x (...) exists but is distinct from y.1 It follows from (CC) that the necessary (contingent) truth of a sentence of the form “α is identical with β”, where “α” and “β” are RRDs of objects x and y respectively, does not require the necessary (contingent) identity of x and y. This is borne out by Gallois’ original example (see 1986, p. 58-63). Taking W to be the actual world, we have: (1) “Mary is identical with Mary” is necessarily true; yet “Mary” RR- designates Mary and Alice, which are only contingently identical. 1 I leave it to the reader to check that in Gallois’ own example (1986, p. 58), on the view he defends (pp. 62-63), and despite his modified characterisation of restricted rigidity, RDC# (1993, p. xx), “Mary” RR-designates Alice (as well as Mary) in W, but designates Mary and not A/ice in W1. Gallois has accepted this in correspondence. In light of (CC), while I agree with Gallois (1993, p. 153) that: (7) (a=b & ◊(a≠b)) → (∃x)(∃y)(x=y & ◊(x≠y)) is a theorem given RDC#, I dispute his defence of it (on p. 153). For, if (CC) is correct, the antecedent of (7) could be true even though a and b are identical in every world (where either exists)! (shrink)