Interpretation as Abduction

Interpretation as Abduction Jerry R. Hobbs, Mark Stickel, Paul Martin, and Douglas Edwards Artificial Intelligence Center SRI International Abstract An approach to abductive inference developed in the TAC- ITUS project has resulted in a dramatic simplification of how the problem of interpreting texts is conceptualized. Its use in solving the local pragmatics problems of reference, compound nominals, syntactic ambiguity, and metonymy is described and illustrated. It also suggests an elegant and thorough integration of syntax, semantics, and pragmatics. 1 Introduction Abductive inference is inference to the best explanation. The process of interpreting sentences in discourse can be viewed as the process of providing the best explanation of why the sentences would be true. In the TACITUS Project at SRI, we have developed a scheme for abductive inference that yields a signi~caut simplification in the description of such interpretation processes and a significant extension of the range of phenomena that can be captured. It has been implemented in the TACITUS System (Stickel, 1982; Hobbs, 1986; Hobbs and Martin, 1987) and has been and is being used to solve a variety of interpretation problems in casualty reports, which are messages about breakdowns in machinery, as well as in other texts3 It~ is well-known that people understand discourse so well ~ because they know so much. Accordingly, the aim of the TACITUS Project has been to investigate how knowledge is used in the interpretation of discourse. This has involved building a large knowledge base of commonsense and do- main knowledge (see Hobbs et al., 1986), and developing procedures for using this knowledge for the interpretation of discourse. In the latter effort, we have concentrated on problems in local pragmatics, specifically, the problems of reference resolution, the interpretation of compound nom- inals, the resolution of some kinds of syntactic ambiguity, and metonymy resolution. Our approach to these problems is the focus of this paper. In the framework we have developed, what the interpre- tation of a sentence is can be described very concisely: ZCharniak (1986) and Norvig (1987) have also applied abductive inference techniques to discoume interpretation. (1) To interpret a sentence: Derive the logical form of the sentence, together with the constraints that predicates impose on their arguments, allowing for coercions, Merging redundancies where possible, Making assumptions where necessary. By the first line we mean "derive in the logical sense, or prove from the predicate calculus axioms in the "knowledge base, the logical form that has been produced by syntactic analysis and semantic translation of the sentence." In a discourse situation, the speaker and hearer both have their sets of private beliefs, and there is a large over- lapping set of mutual beliefs. An utterance stands with one foot in mutual belief and one foot in the speaker's private beliefs. It is a bid to extend the area of mutual belief to include some private beliefs of the speaker's. It is anchored referentially in mutual belief, and when we derive the logi- cal form and the constraints, we are recognizing this refer- ential …

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