By David Lewis
Publisher: Cambridge University Press
Print Publication Year: 1999
Online Publication Date:February 2010
Chapter DOI: http://dx.doi.org/10.1017/CBO9780511625343.015
Subjects: Epistemology and metaphysics
Tim Maudlin claims to derive a contradiction from my account of possible worlds. But the principle that plays the crucial role in Maudlin's refutation is not mine. Maudlin credits it rather to Aristotle. On the one occasion when I considered something resembling Maudlin's Aristotelian principle, I took a dim view of it, saying that if it had the power to support a certain conclusion, then it could equally well support an incompatible conclusion. If the combination of my account of possible worlds with Maudlin's Greek gift turns out to be contradictory, that should come as no surprise.
Here, stated more generally than Maudlin states it, is how the refutation works. Let T be some theory about the nature and structure of modal reality. (It need not be a modal realist theory.) Let T treat some questions about modal reality as mysteries. In other words, T is incomplete: for some statement, M, about modal reality, neither M nor not-M is a theorem of T. Let T treat all statements about modal reality as non-contingent: if any such statement is possibly true, then it is true sirnpliciter. And, finally, let T contain the Aristotelian principle: whatever cannot be refuted in T is possibly true. Now we are in trouble. M cannot be refuted in T, else not-M would be a theorem. Likewise not-M cannot be refuted in T, else M would be a theorem. So, by the Aristotelian principle, both M and not-M are possibly true.