Delimitedness and Trajectory-of-Motion Events

DELIMITEDNESS AND TRAJECTORY-OF-MOTION EVENTS * Michael White Department of Computer and Information Science University of Pennsylvania Philadelphia, PA, USA mwhit e@linc, cis. upenn, edu Abstract The first part of the paper develops a novel, sortally-based approach to the problem of aspectual composition. The account is ar- gued to be superior on both empirical and computational grounds to previous seman- tic approaches relying on referential homo- geneity tests. While the account is re- stricted to manner-of-motion verbs, it does cover their interaction with mass terms, amount phrases, locative PPs, and dis- tance, frequency, and temporal modifiers. The second part of the paper describes an implemented system based on the theoret- ical treatment which determines whether a specified sequence of events is or is not possible under varying situationally sup- plied constraints, given certain restrictive and simplifying assumptions. Briefly, the system extracts a set of constraint equa- tions from the derived logical forms and solves them according to a best-value met- ric. Three particular limitations of the sys- tem and possible ways of addressing them are discussed in the conclusion. 1 Introduction Ever since Verkuyl (1972) first observed that the as- pectual 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 com- ments 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. 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 se- mantic tests (cf. Dowty, 1979, Verkuyl, 1989). Like- wise, the present paper focuses on these empirical issues, in particular the compatibility of a given ex- pression with for- and in-adverbials and the result- ing existential and downward entailments. As an ex- ample of this temporal adverbial test, consider (1) below: (1) (a) John drank beer * in ten minutes. (b) 3ohn drank a pint of beer (*for} in ten minutes. 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 con- sideration iterative, partitive, and other non-basic readings (cf. Moens and Steedman, 1988). Central to previous approaches to aspectual com- position have been attempts to explain the puzzling parallels between count noun phrases and telic sen- tences on the one hand, which have inherently "de- limited" extents, and mass nouns, bare plurals, and atelic sentences on the other, which do not. In con- nection 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 / margari- tas), insofar as they share the …

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