Virtual Polysemy

We present an approach to lexical knowledge representation where different uses of the same word can be conflated into a single meta-entry which encodes regnlarities about sense/usage extensibility. This approach makes it possible to solve lexical anrbiguities by using contextual information (luring language processing to ground underspecified word entries, and can be efficiently implemented within a typed feature structure formalism. 1 I n t r o d u c t i o n One of the central aspects of lexical knowledge, perhaps the most significant in characterizing the creative aspect of language use, is our ability to generate appro~ priate uses of words in coutext. This ability is usually exercized by manipulating semantic and/or syntactic properties of words to achieve desirable collocational settings. Some illustrative examples are given in (1) where ® move can be interpreted as a psychological verb when used transitively with a sentient direct object, * enjoy can take either a noun or verb phrase complement when used in the expeT~ence sense (Pustejovsky, 1991, 1993; Briscoe, Copestake & Boguraev, 1990), , accord is synonymous with either agree or give/granl depending on its valency (Poznafiski & Sanfilippo, 1993), and * the occurrence of a directional argument with swim triggers a shift in aspectual interpretation. (1) a. Please move your car Her sadness moves him b. John enjoys the book John enjoys reading the book e. The two alibis do not accord They accorded him a warm welcome d. John swam for hours John swam across the channel Although the precise nrechanisms which govern lexical knowledge are still largely unknown, there is strong evidence that word sense extensibi[ity is not arbitrary (Atkins &: Levin, 1991; Pustejovsky, 1991, 1994; Ostler Atkius, 1991). [,'or example, the amenability of a *This work was carried out as part of the M'F project at SIIARP Laboratories of Europe. We would like to thank all members of the NLP groul), and in particular Iatl Johnson and Pete Whitelock, for helpful comments and advice. transitive verb such as move to yield either a movement or psychological interpretation ean be generalized to most predicates of caused motion (e.g. agitate, crash, cross, lift, slrike, sweep, unwind) with the causer c o l responding to the stimulus argument and the theme to the experieneer. Similarly, the option of either a noun or verb phrase complement for enjoy can be extended to many other psychological verbs with experiencer subjects (e.g. hale, like, lnvfeO, and verbs of undirected motion in English (e.g. carry, drive, float, push, run, swim, walk) can subcategorize for an expression of completed path so as to yield a telic/directed interpretation (Tahny, 1985; Sanfilippo el al., 1992; Sanfilippo, 11994). Moreover, the metonymical and metaphoric processes which are responsible for sense/usage extcnsious appear to be sul)ject to crosslinguistic variatiou. For example, the "meat vs. animal" alternatkm that is found in English -viz. feed lh.e lamb vs. eal lamb is absent in Eskimo (Nunberg &. Zaencn, 1992) as well as in l)utch where nominal compomlding is used instead -. e.g. lain vs. lamvlees (Copestake & Saniilippo, 1993). Exanrples of this sort show that our ability to exteud word use in context is often systematic or conventiom alized. As Pustejovsky and Boguraev (1993) point out, traditional approaches to lexical representation assume that word use extensibility can be modeled by exhaustively describiug the meaning of a word through closed enumeration of its senses: each sense corresponds to a predefined context. This practice has largely characterized the compilation of dictionary entries in the texicographic tradition and has consequently iniluenced the shape of comlmtational lexicons since the large scale construction of such lexicons has typically involved semiautomatic knowledge acquisition from machine readable dictionaries (Carroll & Grover, 1989). Word sense enumeration provides highly specialized lexical entries, but • it fails to make explicit regularities about word sense cxtensibility which are necessary in promoting compactedness in lexical description, ® it is at odds with our ability to create new word uses in novel contexts, and • it generates massive lexic~d ambiguity. The use of lexical rules to generate different uses of a word fl'om a kernel entry (Copestake gg Briscoe, 199l; Sanfilippo, 1994) provides a 1)rincipled alternative to word sense enumeration and can be made to eater for uovel uses of words. Ilowever, it is not clear whether this practice can address the question of lexical ambiguity suc(:essfully as there is no known general control