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<Paper uid="P88-1012">
  <Title>Interpretation as Abduction</Title>
  <Section position="2" start_page="0" end_page="95" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Abductive inference is inference to the best explanation.</Paragraph>
    <Paragraph position="1"> 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 domain 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 nominals, the resolution of some kinds of syntactic ambiguity, and metonymy resolution. Our approach to these problems is the focus of this paper.</Paragraph>
    <Paragraph position="2"> In the framework we have developed, what the interpretation of a sentence is can be described very concisely: ZCharniak (1986) and Norvig (1987) have also applied abductive inference techniques to discoume interpretation.</Paragraph>
    <Paragraph position="4"> 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.</Paragraph>
    <Paragraph position="5"> By the first line we mean &amp;quot;derive in the logical sense, or prove from the predicate calculus axioms in the &amp;quot;knowledge base, the logical form that has been produced by syntactic analysis and semantic translation of the sentence.&amp;quot; In a discourse situation, the speaker and hearer both have their sets of private beliefs, and there is a large overlapping 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 logical form and the constraints, we are recognizing this referential anchor. This is the given information, the definite, the presupposed. Where it is necessary to make assumptions, the information comes from the speaker's private beliefs, and hence is the new information, the indefinite, the asserted. Merging redundancies is a way of getting a minimal, and hence a best, interpretation. 2 In Section 2 of this paper, we justify the first clause of the above characterization by showing that solving local pragmatics problems is equivalent to proving the logical form plus the constraints. In Section 3, we justify the last two clauses by describing our scheme of abductive inference. In Section 4 we provide several examples. In Section 5 we describe briefly the type hierarchy that is essential for making abduction work. In Section 6 we discuss future directions.</Paragraph>
    <Paragraph position="6"> 2Interpreting indirect speech acts, such u &amp;quot;It's cold in here,&amp;quot; meaning &amp;quot;C1C/wC/ the window,&amp;quot; is not a counterexample to the principle that the minimal interpretation is the best interpretation, but rather can be seen as a matter of achieving the minimal interpretation coherent with the interests of the speaker.</Paragraph>
  </Section>
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