Common Topics and Coherent Situations: Interpreting Ellipsis in the Context of Discourse Inference

COMMON TOPICS AND COHERENT SITUATIONS: INTERPRETING ELLIPSIS IN THE CONTEXT OF DISCOURSE INFERENCE Andrew Kehler Harvard University Aiken Computation Laboratory 33 Oxford Street Cambridge, MA 02138 kehler@das.harvard.edu Abstract It is claimed that a variety of facts concerning ellip- sis, event reference, and interclausal coherence can be explained by two features of the linguistic form in ques- tion: (1) whether the form leaves behind an empty constituent in the syntax, and (2) whether the form is anaphoric in the semantics. It is proposed that these features interact with one of two types of discourse in- ference, namely Common Topic inference and Coherent Situation inference. The differing ways in which these types of inference utilize syntactic and semantic repre- sentations predicts phenomena for which it is otherwise difficult to account. Introduction Ellipsis is pervasive in natural language, and hence has received much attention within both computational and theoretical linguistics. However, the conditions under which a representation of an utterance may serve as a suitable basis for interpreting subsequent elliptical forms remain poorly understood; specifically, past at- tempts to characterize these processes within a single traditional module of language processing (e.g., consid- ering either syntax, semantics, or discourse in isolation) have failed to account for all of the data. In this paper, we claim that a variety of facts concerning ellipsis res- olution, event reference, and interclausal coherence can be explained by the interaction between the syntactic and semantic properties of the form in question and the type of discourse inference operative in establishing the coherence of the antecedent and elided clauses. In the next section, we introduce the facts concerning gapping, VP-ellipsis, and non-elliptical event reference that we seek to explain. In Section 3, we categorize elliptical and event referential forms according to two features: (1) whether the expression leaves behind an empty constituent in the syntax, and (2) whether the expression is anaphoric in the semantics. In Section 4 we describe two types of discourse inference, namely Common Topic inference and Coherent Situation in- ference, and make a specific proposal concerning the interface between these and the syntactic and seman- tic representations they utilize. In Section 5, we show how this proposal accounts for the data presented in Section 2. We contrast the account with relevant past work in Section 6, and conclude in Section 7. Ellipsis and Interclausal Coherence It has been noted in previous work that the felicity of certain forms of ellipsis is dependent on the type of co- herence relationship extant between the antecedent and elided clauses (Levin and Prince, 1982; Kehler, 1993b). In this section we review the relevant facts for two such forms of ellipsis, namely gapping and VP-ellipsis, and also compare these with facts concerning non-elliptical event reference. Gapping is characterized by an antecedent sentence (henceforth called the source sentence) and the elision of all but two constituents (and in limited circumstances, more than two constituents) in one or more subsequent target sentences, as exemplified in sentence (1): (1) Bill became upset, and Hillary …

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