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<Paper uid="P83-1007">
  <Title>PROVIDING A UNIFIED ACCOUNT OF DEFINITE NOUN PHRASES IN DISCOURSE</Title>
  <Section position="1" start_page="0" end_page="0" type="metho">
    <SectionTitle>
PROVIDING A UNIFIED ACCOUNT OF
DEFINITE NOUN PHRASES IN DISCOURSE
</SectionTitle>
    <Paragraph position="0"/>
  </Section>
  <Section position="2" start_page="0" end_page="0" type="metho">
    <SectionTitle>
SRI International
</SectionTitle>
    <Paragraph position="0"/>
  </Section>
  <Section position="3" start_page="0" end_page="0" type="metho">
    <SectionTitle>
1. Overview
</SectionTitle>
    <Paragraph position="0"> Linguistic theories typically assign various linguistic phenomena to one of the categories, syntactic, semantic, or pragmatic, as if the phenomena in each category were relatively independent of those in the others. However, various phenomena in discourse do not seem to yield comfortably to any account that is strictly a syntactic or semantic or pragmatic one. This paper focuses on particular phenomena of this sort-the use of various referring expressions such as definite noun phrases and pronouns-and examines their interaction with mechanisms used to maintain discourse coherence.</Paragraph>
    <Paragraph position="1"> Even a casual survey of the literature on definite descriptions and referring expressions reveals not only defects in the individual accounts provided by theorists (from several different disciplines), but also deep confusions about the roles that syntactic, semantic, and pragmatic factors play in accounting for these phenomena. The research we have undertaken is an attempt to sort out some of these confusions and to create the basis for a theoretical framework that can account for a variety of discourse phenomena in which all three factors of language use interact. The major premise on which our research depends is that the concepts necessary for an adequate understanding of the phenomena in question are not exclusively either syntactic or semantic or pragmatic.</Paragraph>
    <Paragraph position="2"> The next section of this paper defines two levels of discourse coherence and describes their roles in accounting for the use of singular definite noun phrases. To illustrate the integration of factors in explaining the uses of referring expressions, their use on one of these levels, i.e., the local one, is discussed in Sections 3 and 4. This account requires introducing the notion of the centers of a sentence in a discourse, a notion that cannot be defined in terms of factors that are exclusively syntactic or semantic or pragmatic. In Section 5, the interactions of the two levels with these factors and their effects on the uses of referring expressions in discourse are discussed.</Paragraph>
  </Section>
  <Section position="4" start_page="0" end_page="44" type="metho">
    <SectionTitle>
2. The Effects of Different Levels of Discourse
Coherence
</SectionTitle>
    <Paragraph position="0"> A discourse comprises utterances that combine into subconstituents of the discourse, namely, units of discourse that are typically larger than a single sentence, but smaller than the complete discourse. However, the constituent structure is not determined solely by the linear sequence of utterances. It is common for two contiguous utterances to be members of different subconstituents of the discourse (as with breaks between phrases in the syntactic analysis of a sentence); likewise, it is common for two utterances that are not contiguous to be members of the same subconstituent.</Paragraph>
    <Paragraph position="1"> An individual subcoastituent of a discourse exhibits both internal coherence and coherence with the other subconstituents. That is, discourses have been shown to have two levels of coherence. Global coherence refers to the ways in which the larger segments of discourse relate to one another. It depends on such things as the function of a discourse, its subject matter, and rhetorical schema \[Grosz, 1977, 1981; Reichman, 1981 I. Local coherence refers to the ways in which individual sentences bind together to form larger discourse segments. It depends on such things as the syntactic structure of an utterance, ellipsis, and the use of pronominal referring expressions \[Sidner, 1981 I.</Paragraph>
    <Paragraph position="2"> The two levels of discourse coherence correspond to two levels of focusing--global focusing and centering.</Paragraph>
    <Paragraph position="3"> Participants are said to be globally focused on a set of entitie.~ relevant to the overall discourse. These entities may either have been explicitly introduced into the discourse or be sufficiently closely related to such entities to be considered implicitly in focus \[Grosz, 19811 . In contrast, centering refers to a more local focusing process, one relates to identifying the single entity that an individual utterance most centrally concerns \[Sidner, 1979; Joshi and Weinstein, 1981\].</Paragraph>
    <Paragraph position="4"> IThis research was supported in part by the National Science Foundation under Grant MCS-8115105 to SRI International, and Grant MCS81-07290 to the University of Pennsylvania.  The two levels of focusing/coherence have different effects on the processing of pronominal and nonpronominal definite noun phrases. Global coherence and focusing are major factors in the generation and interpretation of nonpronominal def'lnite referring expressions. 2 Local coherence and centering have greater effect on the processing of pronominal expressions. In Section 5 we shall describe the rules governing the use of these kinds of expressions and shall explain why additional processing by the hearer (needed for drawing additional inferences} is involved when pronominal expressions are used to refer to globally focused entities or nonpronominal expressions are used to refer to centered entities.</Paragraph>
    <Paragraph position="5"> Many approaches to language interpretation have ignored these differences, depending instead on powerful inference mechanisms to identify the referents of referring expressions. Although such approaches may suffice, especially for well-formed texts, they are insufficient in general. In particular, such approaches will not work for generation. Here the relationships among focusing, coherence, and referring expressions are essential and must be explicitly provided for. Theories-and systems based on them--will generate unacceptable uses of referring expressions if they do not take these relationships into account. 3</Paragraph>
  </Section>
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