Unification and Grammatical Theory

Abstract

This paper informally presents a new view of grammar that has emerged from a number of distinct but related lines of investigation in theoretical and computational linguistics. Under this view, many current linguistic theories—-including Lexical-Functional Grammar (LFG), Generalized Phrase Structure Grammar (GPSG), Head-Driven Phrase Structure Grammar (HPSG), and categorial grammar (CG)—-fall within a general framework of unification grammar. In such theories the linguistic objects under study are associated with linguistic information about the objects, which information is modeled by mathematical objects called feature structures. Linguistic phenomena are modeled by constraints of equality over the feature structures; the fundamental operation upon the feature structures, allowing solution of such systems of equations, is a simple merging of their information content called unification. Although differences among these theories remain great, this new appreciation of the common threads in research paradigms previously thought ideologically incompatible provides an opportunity for a uniting of efforts and results among these areas, as well as the ability to compare previously incommensurate claims.