Putting the Agents back in the Domain: A Two-Sorted Term-Modal Logic

Abstract: In the present paper syntax and semantics will be presented for an expansion of ordinary n-agent QML with constant domain, non-rigid constants, rigid variables and including both functions, relations, and equality. Further, the number of agents will be specified axiomatically thus ensuring maximal flexibility wrt. the cardinality of the set of agents. Domain, variables, and constants will be partitioned in an agent-part and an object-part and the syntax will be expanded to include strings in which indexes of modal operators are quantified over as wff's of the language. This will enhance expressiveness regarding the epistemic status of agents. Such a term-modal version of the logic K is shown to be sound and complete wrt. the class of (appropriate) frames, and a term-version of S4 is shown to be sound and complete wrt. the class of (appropriate) frames in which the relations are transitive. It should be noted that completeness is shown via the framework of canonical models and thus allows for non-complicated generalizations to other logics than the term-versions of K and S4.