Two morals about a modal paradox

Abstract

Chisholm's paradox serves as an important constraint on our modal theorising. For example, one lesson of the paradox is that widely accepted essentialist theses appear incompatible with metaphysical necessity obeying a logic that includes S4. However, this article cautions against treating Chisholm's paradox in isolation, as a single line of reasoning. To this end, the article outlines two crucial morals about Chisholm's paradox which situate the paradox within a broad family of paradoxes. Each moral places significant constraints on the paradox's solution space. In light of this perspective, the paper applies the two morals to a recently proposed solution to Chisholm's Paradox by Benj Hellie, Murray and Wilson (in: Bennett and Zimmerman (eds) Oxford studies in metaphysics, Oxford University Press, Oxford, 2012). Keywords Metaphysical modality • Chisholm's Paradox • Modal logic • Relativised metaphysical modalityChisholm's Paradox serves as an important constraint on our modal theorising. 1 In response to the paradox, Nathan Salmon (1986, 1989) has proposed that S4 is not a lower bound on the logic of metaphysical necessity. Others, such as Chisholm (1967) himself, have adopted an extremely stringent form of essentialism. More recently, Benj Hellie, Adam Murray, and Jessica Wilson (2012; forthcoming) have developed an interesting view of relativised metaphysical necessity according to which metaphysical necessity exhibits a distinctive type of relativity.The purpose of this article is to emphasise, bolster, and apply two important morals about Chisholm's Paradox. Each moral places significant constraints on the paradox's solution space. The moral of equivalence is that in certain systems of modal logic Chisholm's Paradox is a mere logical variant of a paradox involving no iterated necessity claims. This moral was first noticed by Graeme Forbes (1984, pp. 172-173);