Tableaux for Lewis’s V-family (Yale Weiss)

The Logic and Metaphysics Workshop will meet on October 15th from 4:15-6:15 in room 6494 of the CUNY Graduate Center for a talk by Yale Weiss (GC).

Title: Tableaux for Lewis’s V-family

Abstract: In his seminal work Counterfactuals, David Lewis presents a family of systems of conditional logic—his V-family—which includes both his preferred logic of counterfactuals (VC/C1) and Stalnaker’s conditional logic (VCS/C2). Graham Priest posed the problem of finding systems of (labeled) tableaux for logics from Lewis’s V-family in his Introduction to Non-Classical Logic (2008, p. 93). In this talk, I present a solution to this problem: sound and complete (labeled) tableaux for Lewis’s V-logics. Errors and shortcomings in recent work on this problem are identified and corrected (especially close attention is given to a recent paper by Negri and Sbardolini, whose approach anticipates my own). While most of the systems I present are analytic, the tableaux I give for Stalnaker’s VCS and its extensions make use of a version of the Cut rule and, consequently, are non-analytic. I conjecture that Cut is eliminable from these tableaux and discuss problems encountered in trying to prove this.

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