The Effect of Establishing Coherence in Ellipsis and Anaphora Resolution

THE EFFECT OF ESTABLISHING COHERENCE IN ELLIPSIS AND ANAPHORA RESOLUTION Andrew Kehler Harvard University Aiken Computation Laboratory 33 Oxford Street Cambridge, MA 02138 kehler@das.harvard.edu Abstract This paper presents a new model of anaphoric pro- cessing that utilizes the establishment of coherence relations between clauses in a discourse. We sur- vey data that comprises a currently stalemated ar- gument over whether VP-ellipsis is an inherently syntactic or inherently semantic phenomenon, and show that the data can be handled within a uni- form discourse processing architecture. This archi- tecture, which revises the dichotomy between ellip- sis vs. Model Interpretive Anaphora given by Sag and Hankamer (1984), is also able to accommodate divergent theories and data for pronominal refer- ence resolution. The resulting architecture serves as a baseline system for modeling the role of cohe- sive devices in natural language. 1 Introduction There has been much debate concerning the ap- propriate level of language processing at which to treat VP-ellipsis resolution. Syntactic accounts (Fiengo and May, 1990; Hgik, 1987; Hellan, 1988; Hestvik, 1993; Lappin, 1993; Lappin and McCord, 1990) claim that syntactic material is copied from the antecedent clause and reconstructed in the elided clause, whereas semantic accounts (Dalrym- ple, 1991; Dalrymple et al., 1991; Gawron and Pe- ters, 1990; Hardt, 1992; Kehler, 1993; Klein, 1987) claim this material is retrieved from semantic rep- resentations. This debate is currently deadlocked; indeed a survey of the data seems to indicate that ellipsis must be both a syntactic and semantic phe- nomenon. In Section 2, we examine five types of ellipsis contexts, and show a pattern that has gone unnoticed in the literature. In Section 3 we break the deadlock by presenting a discourse processing architecture from which the correct predictions nat- urally result. We present further evidence for this architecture from pronominal NP reference resolu- tion data in Section 4, and conclude in Section 5. 2 VP Ellipsis Data A simple example of verb phrase (VP) ellipsis is given in sentence (1): (1) Ross likes his mother, and Bill does too. The stranded auxiliary in the second clause (the target clause) indicates the deletion of a verb phrase, a representation for which is to be located from an- other clause (the source clause), in this case, the first clause. Sentence (1) displays a strict/sloppy ambiguity: Bill may like Ross's mother (the strict reading) or his own mother (the sloppy reading). In this section we examine five types of elliptical contexts, and show the following heretofore unno- ticed pattern. 1 When the relationship between the source clause A and the target clause B is what we term parallel (as exemplified by the sentential struc- ture "A and B too", as in sentence (1)), the data indicates that a syntactic representation is recon- structed at the target site. That is, a syntactically- parallel source VP must be available, and recon- struction of this VP in the target clause is subject to syntactic constraints. However, in non-parallel con- structions (for example, contrastive conjunctions ("A but B"), subordinates …

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