Centering in Dynamic Semantics

Centering in Dynamic Semantics Daniel Hardt Department of Computing Sciences Villanova University Villanova, PA 19085 hardt@vill, edu Abstract Centering theory posits a discourse center, a distinguished discourse en- tity that is the topic of a discourse. A simplified version of this theory is developed in a Dynamic Seman- tics framework. In dm resulting sys- tem, the mechanism of center sh/ft allows a simple, elegant analysis of a variety of phenomena involving sloppy identity in ellipsis at~d "pay- check pronom~s". 1 Introduction Centering (Grosz et al., 1995) and Dynamic Semantics* both concern the sequential process- ing 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 expres- sions. 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 dif- ference in the way discourses are viewed in Cen- tering 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. Cen- tering 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. 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 "paycheck pronouns". Since Montague, a major goal of semantics has been to describe a compositional method for con- verting a syntactic representation of a sentence into a logical representation of the sentence mean- ing, and dmn to evaluate that representation with respect to a given context. A primary insight of dynamic semantics is that sentences have a sys- tematic relation to context in two ways: not only are they evaluated with respect to the current con- text, but they also systematically change that con- text. 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 interpre- tation 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 mean- inn 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. Consider the following example involving sloppy identity in VP ellipsis: (1) Tom1 loves his1 cat. John1 does too. [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 "recovery mechanism" involved in sloppy identity; the elided VP is exactly identical to its antecedent. Several authors (Garden% …

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