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<Paper uid="E93-1048">
  <Title>DELIMITEDNESS AND TRAJECTORY-OF-MOTION EVENTS *</Title>
  <Section position="3" start_page="0" end_page="412" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Ever since Verkuyl (1972) first observed that the aspectual class of a sentence depends not only on its main verb (as in Vendler, 1967) but also on its verbal *The author gratefully acknowledges the helpful comments of Jeff Siskind, Mark Steedman, Matthew Stone, and Christy Doran, as well as the support of DARPA N00014-90-J-1863, ARO DAAL03-89-C-0031, NSF IRI 90-16592, Ben Franklin 91S.3078C-1.</Paragraph>
    <Paragraph position="1"> arguments and modifiers, numerous researchers have proposed accounts of this, the problem of ASPEC-TUAL COMPOSITION. Of course, the ultimate aims of these studies have never been to determine the aspectual class of an expression per se -- clearly a theory-internal notion -- but rather to predict the outcomes of certain aspect-related syntactic and semantic tests (cf. Dowty, 1979, Verkuyl, 1989). Likewise, the present paper focuses on these empirical issues, in particular the compatibility of a given expression with for- and in-adverbials and the resulting existential and downward entailments. As an ex- null ample of this temporal adverbial test, consider (1) below: (1) (a) John drank beer * in ten minutes.</Paragraph>
    <Paragraph position="2"> (*for} (b) 3ohn drank a pint of beer in ten  minutes.</Paragraph>
    <Paragraph position="3"> In example (1) we may observe that the appropriate temporal adverbial is determined by the object of the verb drink -- at least as long as we exclude from consideration iterative, partitive, and other non-basic readings (cf. Moens and Steedman, 1988).</Paragraph>
    <Paragraph position="4"> Central to previous approaches to aspectual composition have been attempts to explain the puzzling parallels between count noun phrases and telic sentences on the one hand, which have inherently &amp;quot;delimited&amp;quot; extents, and mass nouns, bare plurals, and atelic sentences on the other, which do not. In connection with this intuitive notion of delimitedness, it has often been observed that mass terms (e.g. beer) and bare plurals (e.g. margaritas) are similar to atelic expressions (e.g. John drink beer / margaritas), insofar as they share the property of REFERENTIAL HOMOGENEITY (reviewed below). This sets  them apart from count noun phrases (eg. a pint of beer) and teiic expressions (e.g. John drink a pint of beer), which do not generally do so.</Paragraph>
    <Paragraph position="5"> Observations such as these led Dowty (1979), Hinrichs (1985) and Krifka (1989, 1992) to incorporate various tests for referential homogeneity into their logical forms in order to account for the temporal adverbial variations. I argue against this move here by showing that it engenders a problem which I shall call THE ACCIDENTAL REFERENTIAL HOMOGENEITY PROBLEM (defined below). As an alternative, I develop in the first part of the paper a novel, sortally-based approach to aspectual composition. The account is argued to be superior not only on empirical grounds, insofar as it dissolves this particular problem, but also on computational grounds, insofar as it justifies employing a feature-based approach. While the account is restricted to manner-of-motion verbs (e.g. run), it does cover their interaction with mass terms, amount phrases, distance and locative modifiers, and temporal adverbials.</Paragraph>
    <Paragraph position="6"> In the second part of the paper, I describe an implemented system based on the theoretical treatment which determines whether a specified sequence of events is or is not possible under varying situationally supplied constraints, given certain restrictive and simplifying assumptions. These assumptions include requiring the sentences to specify trajectory-of-motion events (e.g. Guy jogging from the inn to the bar) which are modeled as continuous constant rate changes of location in one dimension. Briefly, the system extracts a set of constraint equations from the derived logical forms and solves them according to a best-value metric.</Paragraph>
    <Paragraph position="7"> The system is implemented in SCREAMER, Siskind and McAllester's (1993) portable, efficient version of nondeterministic Common Lisp augmented with a general-purpose constraint satisfaction package.</Paragraph>
    <Paragraph position="8"> Three particular limitations of the system and possible ways of addressing them are discussed in the conclusion.</Paragraph>
  </Section>
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