Individual Concepts in Modal Predicate Logic

The article deals with the interpretation of propositional attitudes in the framework of modal predicate logic. The first part discusses the classical puzzles arising from the interplay between propositional attitudes, quantifiers and the notion of identity. After comparing different reactions to these puzzles it argues in favor of an analysis in which evaluations of de re attitudes may vary relative to the ways of identifying objects used in the context of use. The second part of the article gives this analysis a precise formalization from a model- and proof-theoretic perspective. This material has grown out of Chapters 2 and 4 of my PhD thesis Quantification under Conceptual Covers.