Counterpart Semantics. A Foundational study on Quantified Modal Logics
Giovanna Corsi

Abstract:
Counterpart semantics is proposed as the appropriate semantical
framework for a foundational investigation of quantified modal
logics. It turns out to be a limit case of the categorical semantics
of relational universes introduced by Ghilardi and Meloni in 1988. The
main result is a deeper understanding of the interplay between
substitution, quantification and identity whenever modalities are
present. Languages with types and explicit substitutions are the tools
used to clarify such an interplay and to disintangle classical
problems related to modalities in first-order languages. It is shown
that controversial modal principles are neither valid nor
provable. Quine's worries are dispelled.