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<Paper uid="C96-1088">
  <Title>Centering in Dynamic Semantics</Title>
  <Section position="2" start_page="0" end_page="519" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Centering (Grosz et al., 1995) and Dynamic Semantics* both concern the sequential processing of discourses, with particular emphasis on the resolution of pronouns. In Dynamic Semantics, the semantic structure of a discourse gives rise to constraints on the resolution of anaphoric expressions. Centering theory claims that a discourse always has a single topic, or center. Constraints on the resolution of anaphoric expressions arise, in part, from the ways in which the center can change in a discourse. There is an important difference in the way discourses are viewed in Centering and in Dynamic Semantics. In Dynamic Semantics, a discourse is viewed as a monotonic increase in information, as discourse referents are constantly added to the domain of discourse. Centering draws attention to a particular role that a discourse entity can hold; fl:om time to time, t, he current center will be shifted wit.h a new center.</Paragraph>
    <Paragraph position="1"> In this paper, I will implement a simplified version of the centering theory in a dynamic system, and of phenomena involving sloppy identity in ellipsis and &amp;quot;paycheck pronouns&amp;quot;.</Paragraph>
    <Paragraph position="2"> Since Montague, a major goal of semantics has been to describe a compositional method for converting a syntactic representation of a sentence into a logical representation of the sentence meaning, and dmn to evaluate that representation with respect to a given context. A primary insight of dynamic semantics is that sentences have a systematic relation to context in two ways: not only are they evaluated with respect to the current context, but they also systematically change that context. This insight has particular relevance \['or the apparent puzzle presented by sloppy identity and related phenomena. While anaphoric expressions are normally thought to be identical in meaning to dmir antecedents, they receive a different interpretation than their antecedents in these cases. Given the dynamic perspective, the puzzle evaporates: the anaphoric expression and its antecedent might represent exactly the same meaning, since meaninn is fundamentally a potential to be evaluated with respect to some context. What changes is tile context, in the discourse intervening between antecedent and anaphoric expression.</Paragraph>
    <Paragraph position="3"> Consider the following example involving sloppy identity in VP ellipsis: (1) Tom1 loves his1 cat. John1 does too.</Paragraph>
    <Paragraph position="4"> \[loves hisl cat\] The sloppy reading results from a change in context, in which the value of 1 becomes John rather than Tom. This allows an extremely simple account of the &amp;quot;recovery mechanism&amp;quot; involved in sloppy identity; the elided VP is exactly identical to its antecedent. Several authors (Garden% 1991; Hardt, 1.994) have suggested a dynamic account along these lines, arguing that sloppy identity and related phenomena reflect the reassignment of an index in tile discourse context. 2 Alternative approaches postulate complex recovery mechanisms for sloppy identity, such as higher-order matchiug (Dalrymple et al., 1991) or the syntactic matching of parallel dependencies (Fiengo and May, 1994). Below, I will argue that tile dynamic account is more general and empirically adequate, as well as being simpler than alternative accotmts.</Paragraph>
    <Paragraph position="5"> The clynamic account raises the following problem: since the index of the tile initial &amp;quot;controller&amp;quot; is reassioned, it becomes inaccessible in subse- null served tor the discourse center, and the discourse center will always occupy another index as well as 0. We. will us(; the * to designate references to the discourse ce.nter. Thus tim above examt)le will be notated as follows: (2) '.l.'omj, loves his, (:at. John2, does too.</Paragraph>
    <Paragraph position="6"> \[loves his. cat\] In tile first senteIlce, To'm, is the value of illdex 1, and ix also the discourse center, i.e., the value of index 0. The pronoun his* is equivalent to his0, and dins refers to tile discourse center.</Paragraph>
    <Paragraph position="7"> In tile secon(1 sentence, John becomes the value of index 2, and also replaces 5Ibm as the discourse center and thus John becomes the value of index 0.</Paragraph>
    <Paragraph position="8"> This center shift gives rise to the sloppy reading.</Paragraph>
    <Paragraph position="9"> llowever, both 'Ibm and John remain a('eessible in subsequent discourse.</Paragraph>
    <Paragraph position="10"> The paper ix organized as follows: In Section Two, i present a dynamic fl'amework based on the system described in (Muskens, 1996), with extensions for the discourse center, VP ellipsis, and t)ayt:heck t)ronouns. Section Three (:oneerns an &amp;quot;expanded paradigm&amp;quot; for sloppy identity; it; is shown that the t)roposed approach uniformly accounts for a broad range of sloppy identity phenomena, including some not previously examined in the literature. Conclusions and plans for future. work are given in Section l~bur.</Paragraph>
  </Section>
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