Question

I was reading through Collier[21], which is about Lewisian theism, alongside the SEP article on transworld identity, and have assumed that:

The concept of transworld identity (TI) is not necessarily identical to the concept of in-world identity (II).

I suppose a simple argument for (1) would be, If TI ≡ II, then there would be no problem of transworld identity at all. The SEP article seems hesitant about the existence of such a problem, noting how three reasons for the problem's existence can be well-undermined but apparently positing that it is a live issue what the criterion of TI is (or: supposing that it is a live option to debate that criterion rather than abandon TI altogether).

Now, maybe there's an infelicity in (1), or a redundancy, as if identity is necessary in some relevant manner. So we might say:

◊(TI = II) and ◊¬(TI = II) but ¬◊(TI ≡ II), so □¬(TI ≡ II)

... where the equality relation is weaker than identity. Perhaps we could say that identity is generalized enough to be necessary, but equality is then otherwise the same relation but over particulars. (I have seen so many variations on equivalence symbols/concepts as to be lost when it comes to many, or even most, of the details.) But then can we axiomatize a being such that:

∃x(TI(x) = II(x))?

... which is to say, is there a being such that its TI is particularly equal to its II, or the distinction between TI and II is insubstantial for this being? We could, perhaps, reframe the question in terms of Lewisian counterparts:

Letting CI be counterpart identity (identifying something a as a counterpart of b), ∃x(CI(x) = II(x))?

Answer 1

The student's philosophical question pertains to transworld identity (TI) and its distinction from in-world identity (II), exploring if a being's TI can be equivalent to its II, specifically with reference to God, contrasted with human psychological continuity, and discussed within different philosophical viewpoints, such as Locke's, Anselm's, Kant's, and Aristotle's ideas.

Step-by-step explanation:

The discussion centers around the concept of transworld identity (TI) and its relation to in-world identity (II). The student's question is whether there is a being whose TI is equivalent to its II, particularly in the case of a being like God, often discussed in philosophical and theological contexts. Identity, in the philosophical sense, is typically the relation each thing bears just to itself. However, TI involves the question of whether a being in one possible world is the same as a being in another possible world, while II refers to the identity of that being within a single world.

Philosopher John Locke's psychological continuity theory of identity suggests that consciousness and memory constitute individual identity. This concept contrasts with the materialistic view that a being's identity is strictly tied to its physical existence. Conversely, discussing God's existence, Anselm posits that existence itself is a predicate of the divine, challenged by Kant's argument that existence is not a predicate. In metaphysics, Aristotle's notion of potentiality and actuality also touch on questions of being and becoming.

Meanwhile, Lewis' modal realism with counterparts offers a way to consider identity across worlds by introducing counterpart identity (CI), which identifies a being in one world as a counterpart of a being in another.