Adequacy Conditions for Counterpart Theory

Abstract

Abstract David Lewis’s modal realism claims that nothing can exist in more than one world or time, and that statements about how something would have beenare to be analysed in terms of its counterpart. I first explain why the counterpart relation depends on de remodal statements in an intensional language, so that intuitive properties of similarity relations cannot be used to show that the counterpart relation is not an equivalence relation. I then look at test sentences in (the intensional) natural language, and show that none of them provide compelling evidence that a counterpart semantics is needed. David Lewis’s counterpart theory [Lewis 1968] has been with us now for many years. As a metaphysical doctrine, the view that no individual can exist in more than one possible world has had its supporters and its opponents. What has been less discussed is the semanticsof counterpart theory, and it is this question I want to address. My claim will be that there is no clear semantic evidence that we need it. >Lewis’s metaphysical view [Lewis 1986] considers possible but non-actual worlds as equally ‘real’ as the actual world, where the actual world is everything that there is, or perhaps, to use Wittgenstein’s phrase, ‘everything that is the case’. As part of Lewis’s modal realism is the view that, at least for ordinary individuals, people, tables, cups, or double decker buses, nothing can exist in more than one world. This consequence falls naturally out of Lewis’s particular construction of possible worlds as maximal mereological sums of ‘world-mates’, though one can certainly believe, as I am inclined to myself, in a modal realism with genuinely trans-world individuals. It will be useful to connect modal realism with temporal realism, since temporal realism is a widely accepted view. Temporal realism is the view that the present moment is no more real than past or future moments. Temporal realism is not universally accepted. Some believe that only the present is real, others that only the present and past are real, but it is a not uncommon view, and an understanding of modal realism is, I think, helped by the parallel. Lewis also believes that the same individual cannot exist at more than one moment of time, though that need not be essential to temporal realism as such.