In this and the next three chapters I will analyze the concepts which I consider fundamental to the study of information structure. These concepts are: (i) propositional information and its two components presupposition and assertion (Chapter 2); (ii) the identifiability and activation states of the representations of discourse referents in the minds of the speech participants (Chapter 3); (iii) the pragmatic relations topic (Chapter 4) and focus (Chapter 5). Many of the observations in these chapters have been made by other linguists before me, and I will acknowledge my predecessors whenever possible. Other portions, I believe, contain new insights, such as the analysis of the pragmatic relations “topic” and “focus” and of the relationship between the two. In particular, what I believe is new in my treatment, and what prompts me to call it loosely a “theory,” is the idea that an account of information structure must include all three of the sets of concepts listed above and must explain how they relate to each other.

The universe of discourse

I will begin by sketching a simple model of the universe of discourse. In this model, I presuppose the primacy of spoken language over other forms of linguistic communication (see Lambrecht 1986b: Ch. 1). I will therefore always refer to “speakers” and “hearers” (or “addressees”) not to “writers” and “readers.”

Definition of topic

Topic and aboutness

Let me begin with a few remarks about what I will not take “topic” to be in this chapter. First, in keeping with the decision to restrict my research to pragmatic phenomena with grammatical, in particular syntactic, correlates in sentence structure (cf. Section 1.1), I will restrict my attention to sentence topics or clause topics. I will have little to say about the notion of discourse topic, which has more to do with discourse understanding and text cohesion than with the grammatical form of sentences (cf. Halliday & Hasan 1976, Ochs Keenan & Schieffelin 1976b, Van Dijk 1977, Reinhart 1982, Barnes 1985, Van Oosten 1985), although I will sometimes informally use that term to designate a topic expression whose referent is pragmatically salient beyond the limit of a single sentence.

Second, I would like to emphasize from the outset that the concept of topic developed here does not coincide with that of topic (or “theme”) as the “element which comes first in a sentence.” In the framework adopted here, sentence-initial elements may either be topics or foci, hence cannot be identified with either of these categories. The notion of topic/theme as the first element in the sentence is extensively discussed in Prague School research (cf. e.g. the summary in Firbas 1966a) and has been adopted e.g. by Halliday (1967) and Fries (1983).

What is information structure?

There has been and still is disagreement and confusion in linguistic theory about the nature of the component of language referred to in this book as information structure and about the status of this component in the overall system of grammar. The difficulties encountered in the study of information structure are in part due to the fact that grammatical analysis at this level is concerned with the relationship between linguistic form and the mental states of speakers and hearers and that the linguist dealing with information structure must deal simultaneously with formal and communicative aspects of language. Information-structure research neither offers the comfort which many syntacticians find in the idea of studying an autonomous formal object nor provides the possibility enjoyed by sociolinguists of putting aside issues of formal structure for the sake of capturing the function of language in social interaction.

Negative or defeatist views of information-structure research are therefore not uncommon, even among linguists who emphasize the importance of the study of linguistic pragmatics. The following quote concerning the role of topic and focus in linguistic theory illustrates such views: “Terminological profusion and confusion, and underlying conceptual vagueness, plague the relevant literature to a point where little may be salvageable” (Levinson 1983:x). In his own book on pragmatics, Levinson explicitly excludes the analysis of the relationship between pragmatics and sentence form, in particular the analysis of topic-comment structure.

Discourse referents

In the present chapter I will be concerned with the nature of the representations of the referents of linguistic expressions in the minds of interlocutors. In particular, I will be concerned with the changes which these mental representations may undergo in the course of a conversation and with the linguistic forms which code these changes. The set of representations which a speaker and a hearer may be assumed to share in a given discourse will be called the discourse register. As indicated in the remark in Section 2.1, I will tend to neglect the terminological (but not the conceptual) distinction between referents and the mental representations of referents in a discourse. It is primarily the latter that I will be concerned with in the following discussion.

Discourse referents may be either entities or propositions. A proposition may acquire the status of a discourse referent once it is assumed by a speaker to be known to the addressee, i.e. once it has been added to the set of pragmatic presuppositions in the discourse register. The mental representation of such a propositional referent may then be stored in the register together with the representations of entities. Like expressions denoting entities, those denoting presupposed propositions may serve as arguments of a predicate.

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).

In this book, I have tried to present an integrated account of the relationship between the formal structure of sentences and the communicative situations in which sentences are used to convey pieces of propositional information. The account is based on the assumption that this relationship is governed by principles and rules of grammar, in a component called information structure. In this information-structure component, propositions, as conceptual representations of states of affairs, undergo pragmatic structuring according to the discourse situations in which these states of affairs are to be communicated. The pragmatic structuring of propositions is done in terms of a speaker's assumptions concerning the hearer's state of mind at the time of an utterance. Pragmatically structured propositions are then paired with appropriate lexicogrammatical structures.

The assumption that information structure is part of grammar, rather than of general human communicative competence, is based on the existence of a great number of grammatical features and feature combinations – morphosyntactic, prosodic, lexical – which have the unique purpose of signaling information-structure distinctions. These features are grammatical in the sense that the relationship between them and their interpretations is determined by linguistic convention rather than by general principles of communication. Information structure is thus to be distinguished from the general domain of conversational pragmatics, in which context-dependent interpretations of sentences are often determined by non-linguistic factors.

Definition of focus

Focus, presupposition, and assertion

In Chapter 4, I used the term “focus” as a convenient shorthand to refer to the status of certain sentence constituents which systematically differed from topic expressions in their pragmatic function and in their formal expression. It would therefore seem natural to define focus as the “complement of topic.” The complementarity of the two notions is suggested e.g. by the alternative concept pair theme/rheme, whose members are often seen as complementing each other. Using Chafe's characterization of the (topical) subject as the “hitching post for the new knowledge” (cf. Section 4.1.1), we might then say that the focus of a sentence is the “new knowledge hitched to the topic post,” i.e. the new information conveyed about a topic.

Within the present framework, there are at least two reasons for not adopting such a definition. First, if we assume – as I do – that focus has to do with the conveying of new information, and that all sentences convey new information (Section 2.3), all sentences must have a focus. However, not all sentences have a topic (see Sections 4.2.2 and 4.4.4.1). Therefore focus cannot simply be defined as the complement of topic. Second, in the present framework the terms “new knowledge” or “new information” are loose equivalents for the term “pragmatic assertion,” which I defined in Chapter 2 as a proposition that is superimposed on and that includes the pragmatic presupposition (see Section 2.3).