The Logical Analysis of Lexical Ambiguity

THE LOGICAL ANALYSIS OF LEXICAL AMBIGUITY Abstract Theodes of semantic interpretation which wish to capture as many generalizations as possible must face up to the manifoldly ambiguous and contextually dependent nature of word meaning? In this paper I present a two-level scheme of semantic interpretation in which the first level deals with the semantic con- sequences of'syntactic structure and the second with the choice of word meaning. On the first level the meanings of ambiguous words, pronominal references, nominal compounds and metonomies are not treated as fixed, but are instead represented by free variables which range over predicates and func- tions. The context-dependence of lexical meaning is dealt with by the second level, a constraint propaga- tion process which attempts to assign values to these variables on the basis of the logical coherence of the overall result. In so doing it makes use of a set of polysemy operators which map between lexical senses, thus making a potentially indefinite number of related senses available. 1 INTRODUCTION: LEXICAL ASSOCIATION IN A COMPOSITIONAL SEMANTICS A tenet now held with some force among formal semanticists is that the meaning of a complex natural- language expression should be a function of just two things: the meanings of the parts of the expression and the syntactic rule used to form the expression out of those parts. Systems such as Montague Grammar [9] give phrases like "former senator" compositional treatments by first translating them to an expression of intensional logic, and then giving this expression a model-theoretic interpretation in the usual way. The practical relevance of this goal to work in natural lan- guage processing is clear: for any application domain, maximum coverage could be obtained from the same domain-independent set of rules, needing only to add the relevant entries, with their primitive associations of meaning, to the lexicon. ~The work presented here was supported under OARPA contract #N00014-85-C-0016. The views and conclusJons contained in this document are those of the author and should not be inte~reted as necessarily representing the official policies, either expressed or implied, of the Defense Aclvance~ Research Projects Agency or the United States Government. David Stallard, BBN Laboratories Inc. 10 Moulton St., Cambridge, Mass. 02238 An obvious technical issue for this program is raised by the phenomenon of lexical ambiguity. This problem is not one that has been particularly ad- dressed in the Montague Grammar literature. The most obvious approach is simply to make alternative lexical senses separate entries in the lexicon, and to allow these disambiguated lexicat items to give rise to separate syntactic and semantic analyses. The com- putationally unattractive consequences of this are quite clear: the same work must be done over again for each variant. An alternative class of proposals defers the lexical part of the analysis until the rest is done. Hobbs [5] has presented the most detailed general treatment of this type to date. This treatment simply associates each ambiguous lexical item with the logical disjunc- tion of its separate senses. Standard reasoning tech- niques …

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