This book approaches the problems of interpreting language use in terms of interpersonal modelling of beliefs and intentions. It is intended to make issues involved in language understanding, such as speech, text and discourse, accessible to the widest group possible. The most extensive revisions concern the relevance of technical notions of mutual and normal belief, and the futility of using the notion 'null context' to describe meaning. In addition, the discussion of implicature now includes an extended explication of "Grice's Cooperative Principle" .