Research Group
in Analytic Philosophy

Counterpart Theory and Quantified Modal Logic Revisited

    Juhani Yli-Vakkuri (U. of Tartu and U. of Oxford)

20 February 2019  |  15:00  |  Seminari de Filosofia UB


In his classic 1968 paper 'Counterpart Theory and Quantified Modal Logic', David Lewis defines a translation from the language of quantified modal logic (QML) to the extensional first-order language of counterpart theory (CPT). While Lewis proposes to use the translation for testing contested QML principles by checking whether they translate into CPT theorems, he neglects to test his translation by checking whether it takes uncontested QML principles to CPT theorems. I carry out a comprehensive test and show that Lewis's translation takes hardly any standard uncontested principles of modal logic to CPT theorems. I then consider several ways of either modifying the translation or adding postulates to CPT that would give better results, and I find each of them unpromising from the point of view of an advocate of counterpart theory.