The Lexicon and the Boundaries of Compositionality

In its most simple and informal formulation the principle of compositionality expresses an uncontrovertible truth of natural language interpretation, i.e. that the meaning of a complex expression can be derived from the meanings of its parts and the way these parts are syntactically related. The fact that our linguistic system is compositional is nicely confirmed by the capacity of speakers to use a restricted amount of linguistic resources to produce and understand a potentially unlimited number of sentences: “this would be impossible were we not able to distinguish parts in the thoughts corresponding to the parts of a sentence” (Frege 1923). The problem is then how to turn the intuitive statement of compositionality above into a formal constraint on the human language computational system. The lexicon raises some important issues that call into question the compositional nature of natural language interpretation. As Janssen (1997: 420) claims, “compositionality requires that words in isolation have a meaning and that from these meanings, the meaning of a compound can be built.” In other terms, the principle of compositionality seems to presuppose that word meaning is strictly context free, that is to say that “a lexical item must make approximately the same semantic contribution to each expression in which it occurs” (Fodor and Pylyshyn 1988). Prima facie this requirement sharply contrasts with another uncontrovertible fact about natural language, that is to say that lexical meanings are highly context sensitive. Actually, word meaning undergoes continuous modification and modulation in new contexts, and speakers have the ability to “adapt” the meaning of lexical items to fit a specific context and communicative situation (Pustejovsky 1998). A possible way to reconcile meaning variation in context with the requirements imposed by the compositional interpretation of complex expression is to address the former in terms of the notion of homonymy, i.e. the conflation of two symbolic entities under the same form. The fact that in the two sentences The director opened the bank and The water