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<?xml version="1.0" standalone="yes"?> <Paper uid="W91-0209"> <Title>Lexical Operations in a Unification-based Framework</Title> <Section position="2" start_page="0" end_page="90" type="intro"> <SectionTitle> 1 Introduction </SectionTitle> <Paragraph position="0"> In this paper we consider the nature and extent of lexical operations, arguing for a declarative and eomputationally tractable definition of a lexical rule as a component of a unification-based lexicon employing (default) inheritance and typed feature structures.</Paragraph> <Paragraph position="1"> We claim that this notion of lexical rule is capable of capturing the linguistic element of derivational morphological processes as well as metonymic and metaphoric sense extensions, but is not adequate for the statement of certain types of logical metonymy (e.g.</Paragraph> <Paragraph position="2"> Pustejovsky, 1989a). We argue that such operations must be treated as, in part, 'linguistic' because they have morphological and syntactic consequences, undergo 'blocking', are triggered by grammatically-defined type mismatches and involve default interpretations based on lexical organisation. However, we also argue that such default interpretations can be overridden by contextual information on the basis of more general and open-ended 'pragmatic' inference. Our account contrasts with that of, say, Hobbs et al. (1987) who posit an underspecified and impoverished lexical semantic representation which is enriched through an open-ended process of abductive or deductive reasoning with world (or domain) knowledge. Our lexical knowledge representation language does not support general inference, although our lexical semantic representations are often 'richer' than those standardly assumed.</Paragraph> <Paragraph position="3"> A standard example of metonymic sense extension is the use of a word denoting a place to refer to (some of) the people inhabiting that place (e.g. &quot;village&quot;, &quot;palace&quot;). This process seems to involve the foregrounding of one component of the meaning of the place denoting word - we follow Pustejovsky (1989a,b,c) in assuming that the lexical semantic representation of nouns includes information about typical relations which the objects they denote enter into; in particular, the &quot;qualia structure&quot; for such nouns will contain (telic) information which allows direct access to the information that they are inhabited. A well-known example of metaphoric sense extension is that involving use of a word denoting an animal to refer to humans (&quot;John is a pig&quot;, &quot;John is a wombat&quot; etc). Although the sense extension from animals into metaphorical senses denoting humans with some particular characteristic is apparently productive, the actual characteristics involved, and even whether the word can be applied to men or to women or both, cannot be predicted from knowledge of the animal sense. Thus, the properties ascribed to a person by &quot;pig&quot; are arguably no more than stereotypical associations with the animal, rather than central aspects of its meaning / qualia structure. In the case of &quot;wombat&quot; we would argue that the association of foolishness derives from the phonological form of the word, rather than beliefs about the animal. Despite the more associative or analogical nature of metaphorical sense extension, we would argue that there is a core component to such processes which should be expressed in terms of a lexical rule, rather than in terms of general purpose reasoning. As with the metonymic cases (Pustejovsky, 1989c; Briscoe et al., 1990), we believe that the notion of coercion during syntactic and semantic interpretation provides an account of when a metaphorical interpretation will be adopted, and we would like to characterise coercion in terms of possible mappings defined by lexical rules.</Paragraph> <Paragraph position="4"> An example of a derivational morphological process is the addition of the &quot;er&quot; suffix to verbs, typically creating a noun denoting the agent of the action denoted by the verb (e.g.</Paragraph> <Paragraph position="5"> &quot;teach&quot;, &quot;teacher&quot;). There are several apparent differences between this type of process and the metonymic and metaphoric sense extensions considered above. The derivational rule involves a change of syntactic class, it affects the argument structure of the derived predicate, it involves affixation, and although there is a foregrounding of one aspect of the verb meaning, the result would not traditionally be described as a metonymic, or indeed metaphorical, usage. Nevertheless, there are clearly derivational processes which do not affect syntactic class (e.g. &quot;re-program&quot;, &quot;un-reprogrammable&quot;) and of sense extensions which do; for example, countability of nouns changes depending on whether they are interpreted as types, substances or portions (e.g. &quot;There was beer all over the table&quot;, &quot;John drank a beer&quot;). Not all derivational processes affect argument structure (e.g. &quot;unkind&quot;), whilst metonymic sense extensions (e.g. &quot;John enjoyed the film&quot;, John finished the beer&quot;) can, at least given the analyses of Pustejovsky (1989c) and Briscoe et al.</Paragraph> <Paragraph position="6"> (1990). Finally, processes of conversion and derivation can be identical; for example, both &quot;purchase&quot; and &quot;replace&quot; have deverbal nominal forms &quot;purchase&quot; and &quot;replacement&quot;, both nouns can denote the action involved and take appropriate complements (&quot;Bill's purchase of his new car&quot;, &quot;Bill's replacement of John with Mary&quot;), and both can denote the result of the action (&quot;Bill's purchases were many and varied .... Bill's replacement was young&quot;). Traditionally, this latter resultative meaning would be described as metonymic and probably specialised and non-productive. We think that our definition of lexical rule will allow an account of both conversion and derivation as productive syntactic and semantic operations mapping between lexical entries. The difference between metaphorical and metonymic operations is a matter of the degree to which the interaction of the lexical rule with the basic entry determines or circumscribes the eventual interpretation.</Paragraph> <Paragraph position="7"> There are other similarities between sense extension and derivational morphology; clearly, productivity is an issue in both, and in particular, sense extension processes may apparently be blocked (preempted by synonymy), in a way comparable to the situation in derivational morphology (see e.g. Bauer 1983:87f). For example, the regular form &quot;stealer&quot; does not generally occur, apparently because of the availability of &quot;thief&quot;. Another productive metonymic sense extension is that of animal denoting (count) nouns to (mass) nouns denoting their meat (e.g. &quot;lamb&quot;), but this process too is blocked by the presence of a synonymous lexeme with different form (&quot;pig&quot;, &quot;pork&quot;). By representing such processes in terms of lexical rules mapping between entries, we hope to account for blocking in terms of syntactic and semantic identity with an entry defined without recourse to the relevant lexical rule. In addition, we hope to express sense extension processes, and indeed derivational ones, as fully productive processes which apply to finely specified subsets of the lexicon, defined in terms of both syntactic and semantic properties expressed in the type system underlying the organisation of the lexicon.</Paragraph> <Paragraph position="8"> In Briscoe et al. (1990) we offered an account of logical metonymies such as that involved in the interpretation of &quot;Bill enjoyed / regretted that paper&quot;, drawing on Pustejovsky (1989a), in which a unary syntactic rule is used to coerce the entity-denoting NP &quot;that paper&quot; into an event-denoting NP with an underspecified predicate. We argued that a default specification of this predicate is supplied by the qualia structure of the noun and that this is determined by the organisation of the lexicon as a default inheritance network. Specifically, &quot;paper&quot; in the relevant sense will inherit a telic role read ~ and agentive role write t and &quot;enjoy&quot; will by default select the telic role of an NP object, whilst &quot;regret&quot; will select the agentive role. We presented evidence based on corpus data that such default interpretations are appropriate in unmarked informationally-weak contexts, but that they are overridden in marked contexts in which such an interpretation would be clearly inappropriate. The corpus evidence suggests, firstly, that the default interpretation is appropriate with most such logical metonymies and, secondly, that where it is not, the context is sufficient to block it. By contrast, an account such as that of Hobbs et al. (1987) has difficulty explaining why the default interpretation is adopted in the absence of contextual information, unless the effects of lexical organisation are reconstructed in terms of weightings encoding preferences amongst inferences. Whilst this account of the division of labour between default but circumscribed linguistic processes and more open-ended inference remains attractive, the treatment of coercion in this case as a unary syntactic rule, or in Pustejovsky's (1989c) alternative account as a lexical rule, seems inadequate. The interpretation of an individual-denoting nominal or noun phrase as an event-denoting one may be more a matter of systematic vagueness than ambiguity between determinate senses. Pustejovsky (1989a) argues that in examples such as a), b) or c) &quot;long&quot; will have an interpretation in which it modifies the telic or agentive role of &quot;book&quot; because it is an event modifier.</Paragraph> <Paragraph position="9"> a) John bought and read the long book.</Paragraph> <Paragraph position="10"> b) John enjoyed the long book.</Paragraph> <Paragraph position="11"> c) John bought, read and enjoyed the long book.</Paragraph> <Paragraph position="12"> However, this coercion of &quot;book&quot; into, say, &quot;long book to read&quot; does not preclude either an event-denoting or individual-denoting interpretation of the complete NP, as a) and b) demonstrate (where presumably &quot;read&quot; and &quot;bought&quot; select the straightforward referential interpretation, whilst &quot;enjoy&quot; forces another round of coercion). Furthermore, an example like c) which involves a &quot;crossed&quot; interpretation in which &quot;the long book&quot; is simultaneously interpreted as individual- and event-denoting does not seem odd. However, in cases of genuine ambiguity, as opposed to vagueness, such readings are usually blocked (Zwicky & Sadock, 1975): a) John likes landing planes and so does Bill.</Paragraph> <Paragraph position="13"> b) ? Peter's purchase of hi fi took hours and was expensive.</Paragraph> <Paragraph position="14"> c) ? John played with and then ate his lamb.</Paragraph> <Paragraph position="15"> d) John ate and enjoyed the salmon.</Paragraph> <Paragraph position="16"> e) Bill picked up and finished his beer.</Paragraph> <Paragraph position="17"> f) John wrote but later regretted that paper.</Paragraph> <Paragraph position="18"> Thus a) has two, not four, readings in which both John and Bill like watching planes landing or like landing them themselves, but not readings in which the interpretation of &quot;landing planes&quot; varies between conjuncts. Similarly, b) is odd because the first conjunct forces a deverbal event-denoting interpretation of &quot;purchase&quot; whilst the second strongly prefers a resultative reading and c) is odd because the first conjunct prefers the animM-denoting interpretation of &quot;lamb&quot; whilst the second selects the food-denoting one (although the overall preferred interpretation will probably involve treating &quot;played with&quot; to mean something like 'fiddle with or pick at (food)'). By contrast, d-f) all involve moving between individual- and event-denoting readings of the final NPs, but do not seem problematic.</Paragraph> <Paragraph position="19"> These observations suggest to us that an adequate account of the coercion process in these cases will involve positing systematic vaguenesses in interpretation of NPs, perhaps along the lines of type ladder polymorphism (e.g. Partee 8z Rooth 1983) or in terms of lexical operations which apply to the predicates, like &quot;enjoy&quot; which introduce such logical metonymies (rather than to the NP objects of these predicates). In this paper, though we concentrate on ambiguities in interpretation which can he treated in terms of lexical rules which apply to noun entries. We illustrate our approach with reference mainly to the process of 'grinding'. It is well known that ally count noun denoting a physical object can be used in a mass sense to denote a substance derived from that object, when it occurs in a sufficiently marked context. We refer to this as 'grinding' because the context normally suggested is the &quot;Universal Grinder&quot; (see Pelletier and Schubert 1986). So if &quot;a table&quot; is ground up the result can be referred to as &quot;table&quot; (&quot;there was table all over the floor&quot;). Several regular sense extensions can be regarded as special cases of 'grinding', where the extension may have become established. Thus besides the animal/meat examples, trees used for wood (&quot;beech&quot;) have a sense denoting the wood, and so forth. Before we describe this process in detail, we present the framework in which our account will be couched.</Paragraph> </Section> class="xml-element"></Paper>