Jubien, M. 2009. Possibility. Oxford: Oxford University Press.Google Scholar
Lewis, D. 1983. Philosophical Papers, Vol. I. Oxford: Oxford University Press.Google Scholar
Lewis, D. 1986. On the Plurality of Worlds. Oxford: Basil Blackwell.Google Scholar
Salmon, N. 1988. “An Empire of Thin Air.” The Philosophical Review XCVII:237–44. Reprinted in N. Salmon, Metaphysics, Mathematics, and Meaning: Philosophical Papers I, Oxford: Oxford University Press, 2006.Google Scholar
About the article
Published Online: 2014-02-19
Published in Print: 2014-04-01
For advocates of this objection (in part or whole), see Lewis’s references (1986, 98–9). For some more recent supporters of the concern that Lewisian worlds fail to yield unactualized possibilities, see Nathan Salmon (1988) and Michael Jubien (2009, ch. 3).
Sometimes (e.g. 1986, 99) Lewis does not explicitly include the qualification “unactualized.” It is evident from Lewis’s discussion of the thesis, however, that he is concerned with unactualized possibilities. Indeed, otherwise the thesis is plainly false. Clearly some possibilities can be parts of actuality, as is the case with respect to the possibility of you reading this paper. It is unactualized possibilities that are taken to be separate from actuality.
Lewis formally presents the postulate in the following way: P5: ∀x∀y∀z(Ixy & Izy & Cxz. ⊃ x = z). The English readings of the predicates Ixy and Cxy are “x is in possible world y” and “x is a counterpart of y,” respectively (Lewis 1968, 114).
Moreover, note that some possibilities might initially seem to require quantification over sets, when in fact they do not. For example, Lewis (1983, 44) applies counterpart theory to the issue of whether a pair of twin brothers might have been born not as twins but, rather, as unrelated inhabitants of separate planets. Instead of taking a set of which the brothers are members, Lewis takes the mereological sum of the pair of brothers (which is wholly in a possible world). Indeed, it would seem that Lewis’s general preference for counterpart theory is to quantify only over individuals that are wholly in a possible world: “The language of counterpart theory, and the modal language it replaces, had best be understood as quantifying only over possible individuals [i.e. individuals that are wholly in a possible world]. Modifications are called for if we wish to quantify over more of what there is” (1983, 40).
For a helpful discussion of various formulations of haecceitism, including Lewis’s, see Bradford Skow (2008).
For a recent attempt to make sense of a non-qualitative counterpart relation, see Cowling’s (2012) employment of substratum theory.