Against Yagisawa’s Modal Realism

In his book Worlds and Individuals, Possible and Otherwise (2010), Takashi Yagisawa presents and argues for a novel and imaginative version of modal realism. It differs both from Lewis’s modal realism (Lewis 1986) and from actualists’ ersatz accounts (Adams 1974; Sider 2002). Yagisawa draws interesting parallels between tense and modality, and gives a metaphysics of modality which comes close to what the four-dimensionalist says about temporal persistence. He accepts both possible and impossible worlds, arguing that actual entities, mere possibilia and impossibilia are all equally real. Yagisawa argues that the addition of impossibilia to a modal realist account results in ne-grained hyperintensional theories of properties, counterfactuals, intensional attitudes and propositions, on which logical equivalence does not imply identity. Yagisawa argues, Lewis-style, that the theoretical payoff of this account is worth the high ontological cost. Yagisawa’s ontology goes far beyond Lewis’s, but Yagisawa’s modal realism purports to deliver far more. The promise of an extensional, quanti cational analysis of intensional and hyperintensional notions is certainly highly appealing. In this paper, I’ll present two arguments, each of which shows that Yagisawa’s metaphysics is incoherent. The rst argument shows that the combination of Yagisawa’s metaphysics with impossibilia leads to triviality: every sentence whatsoever comes out true. This is so even if Yagisawa accepts a paraconsistent notion of logical consequence, on which contradictions do not entail arbitrary conclusions. The second argument is independent of Yagisawa’s acceptance of impossibilia. It shows that Yagisawa’s metaphysics of possible worlds is incoherent. Using ordinary modal reasoning, I derive a contradiction from Yagisawa’s account of possible worlds. I describe Yagisawa’s modal realism in §2. I present the rst problem for Yagisawa in §3 and consider potential responses on behalf of Yagisawa in §4. The second problem appears in §5. §6 is a brief conclusion.