Journal of Philosophical Logic

, Volume 26, Issue 2, pp 169-180

First online:

On the completeness of first degree weakly aggregative modal logics

  • Peter ApostoliAffiliated withDepartment of Philosophy, University of Toronto

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This paper extends David Lewis’ result that all first degree modal logics are complete to weakly aggregative modal logic by providing a filtration-theoretic version of the canonical model construction of Apostoli and Brown. The completeness and decidability of all first-degree weakly aggregative modal logics is obtained, with Lewis’s result for Kripkean logics recovered in the case k=1.