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<Paper uid="J88-2004">
  <Title>ASPECT, ASPECTUAL CLASS, AND THE TEMPORAL STRUCTURE OF NARRATIVE</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 INTRODUCTION
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    <Paragraph position="0"> This paper consists of two parts. 1 The first part (sections 2-5) discusses aspect and other varieties of commonsense knowledge about time as manifested in language. The second part (sections 6-8) discusses how this knowledge is employed in understanding extended narratives. This preliminary section spells out the paper's principles and aspirations.</Paragraph>
    <Paragraph position="1"> A major influence on this paper has been the study of commonsense knowledge and reasoning in the paradigm established in Hayes 1985 (1979), Hobbs and Moore 1985, and Hobbs et al., 1985, 1986. The paper proceeds from the premise that commonsense studies and natural language semantics are closely interdependent: natural-language semantics is essentially incomplete without a theory of the commonsense world, for which natural language provides key empirical data. These data are of two kinds, lexical and grammatical. So far, mostly lexical data have been used in work on knowledge representation: the contexts of a given word, the structure of semantic fields, and metaphorical uses (Hobbs 1984:284, 1985a:3). This paper suggests that in working on core knowledge (time, space, causality), it is imperative to recognize grammatical categories as powerful, and language specific, tools of organizing conceptual space.</Paragraph>
    <Paragraph position="2"> Among grammatical categories particularly important are those that allow, and indeed force, the language user to choose between alternative ways of viewing the same object or situation. I will call such categories subjective. A paradigmatic example of a subjective grammatical category is aspect. (In fact, the term aspect came into being as an attempt to translate the Russian term vid (&amp;quot;view&amp;quot;); see Lyons 1977:705.) Subjective grammatical categories are important for two reasons.</Paragraph>
    <Paragraph position="3"> First, they suggest restrictions on the formalism: since Copyright 1988 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 CL 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/88/010029-43503.00 Computational Linguistics, Volume 14, Number 2, June 1988 29 Alexander Nakhimovsky Aslaect, Aspectual Class, and the Temporal Structure of Narrative language users can easily switch between alternative views of the same entity, the formalism should provide for alternative representations related by a simple and general operation. (Bunt 1985:39-40 makes a similar point with respect to the opposition mass-count.) Second, subjective grammatical categories show that the corresponding conceptual distinctions reflect our alternative ways of viewing things rather than intrinsic properties of things. There are intrinsic properties that interact with subjective distinctions, and in a language that does not have a well-articulated subjective grammatical opposition, the intrinsic and the subjective become easily confused. An example of such a confusion is, I believe, the well-known taxonomy of events, processes, and states (Mourelatos 1981), which is discussed in Section 4.3.</Paragraph>
    <Paragraph position="4"> It follows that in designing the primitives of our semantic representations it is essential to look at data across languages, paying particular attention to subjective grammatical categories. (They are easy to identify because they are notoriously difficult to learn how to use correctly, possibly because of having to internalize a new global operation on the mental model.) Decades of linguistic research can thus be brought to bear on the enterprise of formalizing commonsense knowledge.</Paragraph>
    <Paragraph position="5"> Conversely, this enterprise makes it possible to pose with greater precision the old problem of how language, and in particular its grammatical categories, influences our thought and vision of the world.</Paragraph>
    <Paragraph position="6"> Formalizations of the commonsense may or may not turn out to be language and culture specific, but they will have to have features particular to our planet and the species. Such accidental parameters of human existence as the duration of a year, the length of an arm, and the temperature of the human body are universal constants that play an important role in our reasoning: they determine how we factor a continuous parameter like temperature or time into a quantity space (in the sense of Forbus 1985:80-1). Therefore, and contrary to a widespread view, any rigorous semantics of natural language has to concern itself with definitions of extensional concepts. Such definitions obviously belong in the lexicon. In this paper, lexicon is understood to be a repository of both grammatical and commonsense knowledge, indexed by lexical items. This view of the lexicon, advocated also in Hobbs et al., 1985, has important antecedents in Soviet and European linguistics (Apresjan 1974, Wierzbicka 1985).</Paragraph>
    <Paragraph position="7"> A second major influence on this paper is the notion of computational modeling of natural-language semantics (Hendrix and Moore 1979), i.e., the idea that semantical objects associated with natural-language expressions are (typed) data structures, together with inference procedures that operate on them. These data structures form an internal representation language that may or may not in turn be endowed with a semantics of its own. In what follows I assume that semantical objects are frames and collections of frames, and the basic :ypes include frame and slot label (cf. Creary and Pollard 1985, and Hirst 1987, ch.3). There are sortal predical~.es, or simply sorts, that are defined on frames and organize them into an ISA hierarchy.</Paragraph>
    <Paragraph position="8"> The', first cut in the hierarchy is between flames representing objects and flames representing situations persis :ing or evolving in time. (Loosely following Hayes 1985, I call the latter histories.) Orthogonal to this distinction is the one between generic flames or types, and their instances or tokens: tokens, but not types, have a slot for a spatio-temporal location. I will thus speak of history types (h-types) and history tokens (htokens); when the type-token distinction is irrelevant I will simply say &amp;quot;history.&amp;quot; H-types can be of various degrec.s of generality (cf. the representations of read, read a book, read a book for an hour; all of these, however, are types of which the representation of Jon read a book for an hour is a token). Associated with each h-type is a set of slot labels and selectional restrictions on them, usually a conjunction of sortal predicates (Hobbs et al., 1986).</Paragraph>
    <Paragraph position="9"> Whether types or tokens, the semantical objects of natural-language semantics are only partially specified, and &amp;quot;:nore partial&amp;quot; objects are embeddable, with some provisions for nonmonotonicity, into less partial ones. I assume that representations of lexical items in the lexicon form a discrete level of partiality. The subject of the first part of the paper can then be stated as follows: What is the knowledge about events that is part of lexical meanings? How can it be coded in the h-types of the lexicon, and how is it used as lexical meanings are combined and embedded into more precisely specified strucrares? In the end, what it all boils down to is an extended argument for some slots in the lexical representations of histories and a few sortal predicates on h-types representing aspectual classes.</Paragraph>
    <Paragraph position="10"> Finally, with respect to narrative understanding, a major itffluence has been the idea that such understanding means constructing, or &amp;quot;building a good structure&amp;quot; (Bruce 1981:283), so that the semantic value of a lingui~;tic unit (phrase, sentence) is its contribution to the emerging representation of discourse. This idea, in one o1' those parallel developments that do not seem to be purely coincidental, emerged at about the same time in the Reader-Response school of literary criticism (e.g., Tompkins 1980), in model-theoretic semantics (Kamp 1981, Heim 1982) and in AI approaches to discourse; in combination with the idea of computational modeling it first clearly appears in Webber 1979 (see also Webber, this volume).</Paragraph>
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