In this book, first published in 1975, Dr Kempson argues that previous work on presupposition - whether in philosophy or linguistics - has been mistakenly based on a conflation of two different disciplines: semantics, the study of the meanings assigned to the formal system which constitutes a language, and pragmatics, the study of the use of that system in communication. The first part of the book deals generally with the nature of semantics in linguistic theory and its formal representation within a transformational grammar; Dr Kempson argues against incorporating the relation of presupposition within such a grammar. The second part provides a pragmatic account of the foundations of a theory of communication and its detailed application to the problems raised by presupposition. The book is intended for those studying both philosophy and linguistics and also for those sociolinguists and psychologists with a more general interest in the theory of communication.