Getting at Discourse Referents

GETTING AT DISCOURSE REFERENTS Rebecca J. Passonneau UNISYS, Paoli Research Center P.O. Box 517, Paoli, PA 19301, USA ABSTRACT I examine how discourse anaphoric uses of the definite pronoun it contrast with similar uses of the demonstrative pronoun thai. Their distinct contexts of use are characterized in terms of two contextual features--perslstence of grammati- cal subject and persistence of gr,~mmatical form--which together demonstrate very clearly the interrelation among lexical choice, grammati- cal choices and the dimension of time in signalling the dynamic attentional state of a discourse. 1 Introduction Languages vary in the number and kinds of gram- matical distinctions encoded in their nominal and pronominal systems. Language specific means for explicitly mentioning and re-mentioning dis- course entities constrain what Grosz and Sidner refer to as the linguistic structure of discourse [2]. This in turn constrains the ways in which dis- course participants can exploit linguistic structure for indicating or inferring attentional state. At- tentional state, Grosz and Sidner's term for the dynamic representation of the participants' focus of attention [2], represents--among other things- which discourse entities are currently most salient. One function of attentional state is to help resolve pronominal references. English has a relatively impoverished set of definite pronouns in which gender is relevant only in the 3rd person singu- lar, and where number---a fairly universal nominal category--is not relevant in the 2nd person. Yet even within the English pronominal system, there is a semantic contrast that provides language users with alternative means for accessing the same pre- viously mentioned entities, therefore providing in- vestigators of language with an opportunity to ex- plore how distinct lexicogrammatical features cor- relate with distinct attentional processes. This is the contrast between demonstrative and non- demonstrative pronouns. In this paper I examine how certain uses of the singular definite pronoun it contrast with similar uses of the singular demon- strative pronoun that. I present evidence that the two pronouns it and that have pragmatically distinct contexts of use that can be characterized in terms of a remarkably simple set of preconditions. First, in §2 1 delineate the precise nature of the comparison made here. In §3.1, I describe the methods I used to collect and analyze a set of data drawn from ordinary con- versational interactions. The result of my statisti- cal analysis was a single, highly significant multi- dimensional distributional model, showing lexieai choice to be predicted by two features of the lo- cal context. In §3.2, I summarize the statistical results. They were strikingly clearcut, and pro- vide confirmation that grammatical choices made by participants in a dialogue prior to a particular point in time correlate with lexical choice of either participant at that time. Of over a dozen different variables that were examined, two alone turned out to have enor- mons predictive power in distinguishing between the typical contexts for the two pronouns. Very briefly, the first variable, persistence of gram- matical subject, indicates whether both the an- tecedent and pronoun were subjects of their re- spective clauses. The …

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