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<Paper uid="J81-4001">
  <Title>Focusing for Interpretation of Pronouns I</Title>
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1. Introduction
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    <Paragraph position="0"> Traditionally researchers have defined the problem of comprehending anaphoric expressions as one of determining the antecedent of an anaphoric expression, that is, determining to which word or phrase an anaphoric expression refers or &amp;quot;points&amp;quot;. Recent studies in both artificial intelligence and linguistics have demonstrated the need for a theory of the comprehension of anaphoric expressions, a theory that accounts for the role of syntactic and semantic effects, as well as inferential knowledge in explaining how anaphors are understood. In this paper a new theory, based on the concept of focusing in the discourse, is introduced to explain the interpretation of pronouns.</Paragraph>
    <Paragraph position="1"> Before a theory can be given, and before even the difficulties in interpreting anaphors 2 can be discussed, I The research reported in this paper was supported in part by the Advanced Research Projects Agency under contract No. N0014-77-C-0378. Research reported here was also done at the Artificial Intelligence Laboratory of the Massachusetts Institute of Technology. Support for the laboratory's artificial intelligence research is provided in part by the Advanced Research Projects Agency of the Department of Defense under ONR contract N00014-75-0643. I would also like to thank Bob Bcrwick, Barbara Grosz, David Israel, and the AJCL referees for their help in preparing this paper.</Paragraph>
    <Paragraph position="2"> 2 I use the term &amp;quot;anaphor&amp;quot; for an anaphoric expression, and I use &amp;quot;anaphora&amp;quot; in its traditional meaning, that is, as the device of using a word or phrase &amp;quot;to point back.&amp;quot; we must first re-consider what an antecedent is. The traditional definition encounters difficulty right from the start; it is founded on the notion that one word in a sentence refers or points back to another word or phrase in the (same or another) sentence. But words don't refer back to other words \[Morgan 1978\]; people use words to refer to entities in the world. In particular they use pronouns to refer to entities which have already been mentioned in a discourse. Since an anaphoric phrase does not refer to an antecedent, one might want to claim that both the antecedent and the anaphor co-refer to the same entity. That description is adequate for sentence sl, sl I think green apples taste best and they make the best cooking apples too.</Paragraph>
    <Paragraph position="3"> though not for discourse D1, where there is no antecedent phrase in the discourse that co-refers with the pronoun &amp;quot;they.&amp;quot; DI-1 My neighbor has a monster Harley 1200.</Paragraph>
    <Paragraph position="4"> 2 They are really huge but gas-efficient bikes.</Paragraph>
    <Paragraph position="5"> Rather than view antecedence as co-reference, one might propose that antecedence is a kind of cognitive pointing, the kind of pointing that causes &amp;quot;they&amp;quot; and &amp;quot;green apples&amp;quot; to point (somehow) to the same class of entities in one's mind. This proposal is problematic for the same reason that co-reference is: people use pronouns when there is no other noun phrase in the Copyright 1981 by the Association for Computational Linguistics. Permission to copy without fee all or part of this material is granted provided that the copies are not made for direct commercial advantage and the Journal reference and this copyright notice are included on the first page. To copy otherwise, or to republish, requires a fee and/or specific permission. 0362-613X/81/040217-15501.00 American Journal of Computational Linguistics, Volume 7, Number 4, October-December 1981 217 Candace L. Sidner Focusing for Interpretation of Pronouns discourse that points to the right mental entity. In D1, &amp;quot;they&amp;quot; refers to bikes which are Harley 1200's as a group, while &amp;quot;a monster Harley 1200&amp;quot; mentions only some particular Harley 1200. &amp;quot;They&amp;quot; seems to be able to refer when used with the previously mentioned phrase &amp;quot;a monster Harley 1200&amp;quot; without the two phrases either co-referring or co-pointing.</Paragraph>
    <Paragraph position="6"> If an anaphor does not refer to an antecedent phrase, and if it need not always co-refer with its apparent antecedent (as in D1), then anaphor interpretation is not simply finding the antecedent. Nevertheless the concept of antecedence as pointing back does seem to capture some aspect of the comprehension of anaphors, for when certain antecedent words are missing from a discourse, people often fail to understand what is being said.</Paragraph>
    <Paragraph position="7"> Let us define the problem of interpreting and understanding an anaphor in the following way. The phrase &amp;quot;green apples&amp;quot; in sl, when syntactically and semantically interpreted, is said to specify a cognitive element in the hearer's mind. In the computational model of that process, this element is a database item, which might be represented by Apples2 in by the schema below: Phrase76: string: &amp;quot;green apples&amp;quot; context: speakerl think * tastes best specifies: Apples2 Apples2: super-concept: apples color: green used-for: cooking The speaker uses the information in a cognitive representation like Apples2 above to choose the phrase &amp;quot;green apples&amp;quot; in sl. The hearer then uses the phrase &amp;quot;green apples&amp;quot; plus the syntactic and semantic interpretation of the rest of the sentence to locate a similar cognitive element in his own mind; it may be slightly different because the hearer may not associate use in cooking with green apples. A cognitive element, such as Apples2, is called the specification of &amp;quot;green apples.&amp;quot; These elements, present in the memories of speaker and hearer, are of course related to other cognitive elements in their memories.</Paragraph>
    <Paragraph position="8"> What is the relation of specifications to the real world? One might like to claim that a reference relation exists between specified cognitive elements and objects in the world, but since referring is what people do with words, this relation is problematic for cognitive elements. Instead, specifications are said to represent the objects referred to; that is, they bear a well-structured correspondence to objects in the world.</Paragraph>
    <Paragraph position="9"> Apples2, the specification of &amp;quot;green apples,&amp;quot; represents the objects that are green apples. For phrases such as &amp;quot;Santa Claus,&amp;quot; where there is no real world object to represent, a specification represents the mental schema to which are attached the properties normally associated with this imaginary person.</Paragraph>
    <Paragraph position="10"> The phrase &amp;quot;they&amp;quot; in sl also specifies a cognitive element, namely the same one that &amp;quot;green apples&amp;quot; does. Since the two bear the same relation to the representation Apples2, I say that they &amp;quot;co-specify&amp;quot; that memory element, or alternatively, that the interpretation of &amp;quot;green apples&amp;quot; is the co-specifier of the interpretation of &amp;quot;they.&amp;quot; Co-specification, unlike co-reference, allows one to construct abstract representations and define relationships between them which can be studied in a computational framework.</Paragraph>
    <Paragraph position="11"> With co-reference no such use is possible, since the object referred to exists in the world and is not available for examination by computational processes.</Paragraph>
    <Paragraph position="12"> Even if a phrase and a pronoun do not co-specify, the specification of the phrase may be used to generate the specification of a pronoun. For example, in D1 &amp;quot;they&amp;quot; does not co-specify with the apparent antecedent phrase &amp;quot;a monster Harley 1200,&amp;quot; but rather it refers to the class of Harley 1200's of which the apparent antecedent is an instance. Thus anaphor interpretation is not simply a matter of finding the corresponding cognitive element that serves as the specification of the anaphor; some additional process must generate a specification for the anaphor from the related phrase &amp;quot;a monster Harley 1200.&amp;quot; The concepts of specification and co-specification capture the &amp;quot;pointing back&amp;quot; quality of antecedence, and also permit us to formulate an explanation of anaphor interpretation that avoids the pitfalls of the concept of antecedence. Anaphor interpretation can be studied as a computational process that uses the already existing specification of a phrase to find the specification for an anaphor. The process uses a representation of the discourse preceding the anaphor to encode the syntactic and semantic relationships in each sentence as well as co-specification relationships between phrases. 3 These definitions in themselves do not constitute a theory of anaphor interpretation.</Paragraph>
    <Paragraph position="13"> They do, however, make possible a succinct statement of the problem: how does one determine the specification of a anaphor? Also, since we suspect that the specification of an apparent antecedent phrase plays some role in choosing an anaphor's specification, we may ask, just what is this role? We hope for a direct answer to these questions, but before one can be given, let us consider how a theory of interpretation ought to address these questions. A brief look at the</Paragraph>
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