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<Paper uid="J93-4003">
  <Title>Indexical Expressions in the Scope of Attitude Verbs</Title>
  <Section position="2" start_page="0" end_page="0" type="abstr">
    <SectionTitle>
1. Introduction
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    <Paragraph position="0"> A sentential theory of attitudes holds that propositions (the things that agents believe and know) are sentences of a representation language. The idea has an obvious appeal to AI workers, who rely heavily on representation languages. Moore and Hendrix (1982) gave the classic statement of the case for a sentential theory of attitudes. Konolige (1986), Haas (1986), and Perlis (1988) are among the authors who have applied sentential theories to AI problems.</Paragraph>
    <Paragraph position="1"> A central problem for any theory of attitudes is the opacity of NPs in the scope of attitude verbs. Suppose we take a sentence containing an occurrence of the noun phrase NP1 and we replace that occurrence with another noun phrase NP2 that refers to the same individual. In many cases, the substitution will preserve the truth value of the sentence. If &amp;quot;Superman&amp;quot; and &amp;quot;Clark Kent&amp;quot; refer to the same man, then &amp;quot;Superman was born on Krypton&amp;quot; and &amp;quot;Clark Kent was born on Krypton&amp;quot; have the same truth value. However, if NP1 and NP2 occur in the scope of an attitude verb, the two sentences might have different truth values. If &amp;quot;Superman&amp;quot; and &amp;quot;Clark Kent&amp;quot; refer to the same man, and Lois Lane knows this man, the sentence &amp;quot;Lois thinks that Superman was born on Krypton&amp;quot; might be true even though &amp;quot;Lois thinks that Clark Kent was born on Krypton&amp;quot; is false. Then the occurrence of &amp;quot;Superman&amp;quot; in the first sentence is called an opaque occurrence.</Paragraph>
    <Paragraph position="2"> Current versions of the sentential theory can explain many examples of opacity, but they have trouble when the opaque NP is an indexical. 'T' and &amp;quot;now&amp;quot; are typical indexicals. When 'T' occurs in an English utterance, it refers to the speaker of that utterance. When &amp;quot;now&amp;quot; occurs in an English utterance, it refers to the time when the  * Department of Computer Science, The University at Albany, 1400 Washington Avenue, Albany, NY 12222 (c) 1994 Association for Computational Linguistics  Computational Linguistics Volume 19, Number 4 speaker produces the utterance. In general, indexicals are words and phrases whose reference is fixed by a property of the utterance they occur in. Demonstratives are a class of phrases akin to indexicals, whose reference often depends on gestures that accompany an utterance. If I point at a book and say &amp;quot;Give me that book,&amp;quot; the phrase &amp;quot;that book&amp;quot; refers to the book I pointed at. Indexicals and demonstratives occur constantly in human speech, and they present crucial problems for any theory of propositional attitudes. In particular, it is essential to explain how an indexical in the scope of an attitude verb can be opaque.</Paragraph>
    <Paragraph position="3"> If we adopt a sentential theory of attitudes, it is natural to suggest that the proposition expressed by an utterance is also a sentence of a representation language. This leads to a straightforward account of the semantics of attitude verbs. In Section 2 I will describe this approach and show why it fails to explain the opacity of indexicals in the scope of attitude verbs. In Section 3 1 will describe a nonsentential semantics for attitude verbs due to Crimmins and Perry (1989). This theory can explain the opacity of indexicals. In Section 4 1 will describe a new version of the sentential semantics for attitude verbs, which incorporates some of Crimmins and Perry's ideas. This theory denies that the proposition expressed by an utterance is a sentence in a representation language. It follows (given a sentential theory of attitudes) that an utterance expresses a proposition that no one can believe or know. This sounds paradoxical, but I will argue that the new theory explains the opacity of indexicals while maintaining the advantages of a sentential theory of attitudes.</Paragraph>
  </Section>
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