Counterfactuality, reduction, and the argument for possible worlds from theoretical virtue

Abstract

This dissertation discusses three important topics in the philosophy of possible worlds.

The first topic concerns how best to formulate what is widely believed to be the most powerful argument for possible worlds, namely the indispensability argument for possible worlds, or, as it is arguably better called, the argument for possible worlds from theoretical virtue. Standard formulations of this argument beg the question against anti-realists about possible worlds by presupposing the existence of controversial entities such as theories that anti-realists can, and arguably should, reject. This dissertation formulates a new version of the argument for possible worlds from theoretical virtue that does not presuppose the existence of such entities and which therefore avoids begging the question against anti-realists. It also shows how anti-realists can formulate the converse to this argument - the argument against possible worlds from theoretical virtue - without presupposing the existence of entities such as theories they should arguably reject.

The second topic concerns the nature of reduction. Two notions of reduction that are able to play an important role in theory choice are discussed: identity reduction and structural reduction. In effect, a sentence is identity reducible to another sentence if the two sentences represent the same state of affairs; whereas, a sentence is structurally reducible to another sentence if, in addition to representing the same state of affairs, the reducing sentence plays an explanatory role with respect to the structural features associated with the sentence being reduced, where examples of structural features include intrinsicality, qualitivity, positivity, and resemblance making. To add content to this second less familiar notion of reduction, there is an extensive discussion on how sentences can play such an explanatory role, and why it is good for theories to contain such reductions.

The third topic concerns what reductions different theories of possible worlds can provide. It is widely believed that one major reason for believing that there are possible worlds is that realist theories can provide reductions anti-realist theories cannot provide. Two alleged cases of such reductions are discussed: the reduction of possibility to non-modal notions, and the reduction of counterfactuality to possibility and non-modal notions. In the first case, it is argued that possibility can be identity reduced in terms of non-modal notions regardless of whether there are possible worlds. In the second case, it is argued that, if counterfactuality can be structurally reduced in terms of possibility and non-modal notions given there are possible worlds, then it can also be so reduced if there are no possible worlds. These arguments, if correct, go some way towards undermining the claim that realist theories about possible worlds are better at providing reductions than anti-realist theories, and hence go some way towards undermining what is widely believed to be one of the most important reasons for believing in possible worlds. Show more