This book proposes a theory of the relationship between the structure of sentences and the linguistic and extra-linguistic contexts in which sentences are used as units of propositional information. It is concerned with the system of options which grammars offer speakers for expressing given propositional contents in different grammatical forms under varying discourse circumstances. The research presented here is based on the observation that the structure of a sentence reflects in systematic and theoretically interesting ways a speaker's assumptions about the hearer's state of knowledge and consciousness at the time of an utterance. This relationship between speaker assumptions and the formal structure of the sentence is taken to be governed by rules and conventions of sentence grammar, in a grammatical component which I call information structure, using a term introduced by Halliday (1967). In the information-structure component of language, propositions as conceptual representations of states of affairs undergo pragmatic structuring according to the utterance contexts in which these states of affairs are to be communicated. Such pragmatically structured propositions are then expressed as formal objects with morphosyntactic and prosodic structure.

My account of the information-structure component involves an analysis of four independent but interrelated sets of categories. The first is that of propositional information with its two components pragmatic presupposition and pragmatic assertion. These have to do with the speaker's assumptions about the hearer's state of knowledge and awareness at the time of an utterance (Chapter 2).