A Manual of Intensional Logic: 2nd Edition

Intensional logic is the technical study of such "intensional" phenomena in human reasoning as modality, knowledge, or flow of time. These all require a richer semantic picture than standard truth values in one static environment. Such a picture is provided by so-called "possible worlds semantics," a paradigm which is surveyed in this book, both as to its external sources of motivation and as to the internal dynamics of the resulting program.