Lexical rules in constraint-based grammars

Lexical rules have been used to cover a very diverse range of phenomena in constraint-based grammars. Examination of the full range of rules proposed shows that Carpenter's (1991) postulated upper bound on the length of list-valued attributes such as SUBCAT in the lexicon cannot be maintained, leading to unrestricted generative capacity in constraint-base formalisms utilizing HPSG-style lexical rules. We argue that it is preferable to subdivide such roles into a class of semiproductive lexically governed genuinely lexical rules, and a class of fully productive unary syntactic rules. We develop a restricted approach to lexical rules in a typed default feature structure (TDFS) framework (Lascarides et nl. 1995; Lascarides and Copestake 1999), which has enough expressivity to state, for example, rules of verb diathesis alternation, but which does not allow arbitrary manipulation of list-valued features. An interpretation of such lexical rules within a probabilistic version of a TDFS-based linguistic (lexical and grammatical) theory allows us to capture the semiproductive nature of genuinely lexical rules, steering an intermediate course between fully generative or purely abbreviatory rules. We illustrate the utility of this approach with a treatment of dative constructions within a linguistic framework that borrows insights from the constraint-based theories: HPSG, UCG, (Zeevat, Klein, and Calder 1987) and construction grammar (Goldberg 1995). We end by out lining how our approach to lexical rules allows for a treatment of passive, nand recursive affixation, which are generally assumed to require unrestricted list manipulation operations.