Lexical-Functional Grammar

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A generative theory from the class of unification grammars that was developed by J. Bresnan and R.Kaplan at the end of the 1970s, and was influenced by relational grammar. The most comprehensive description of the theory is to be found in Bresnan (1982). Lexical-Functional Grammar (LFG) attaches great meaning to the grammatical relations like subject, direct object, and indirect object, and includes them in a small class of universal grammatical functions (together with other syntactic roles, such as adjunct and free adjunct). These grammatical functions are the primitive concepts in LFG. LFG’s point of departure is that many of the syntactic regularities which were described by transformations in transformational grammar, are of a lexical nature and, therefore, can be represented in the lexicon. The grammatical formalism of LFG distinguishes two levels of syntactic representation, constituent structure and functional structure, which are generated in parallel from the annotated phrase structure rules of the grammar. Without annotations, (i.e. feature equations that make up the functional structure), these rules are context-free rules, which generate local trees with atomic category symbols. They are governed by a version of X-bar theory. The functional structure of a constituent is a feature structure in the sense of unification grammar. Grammatical functions like SUBJ (subject), OBJ2 (indirect object) and PRED (predicate) as well as morphosyntactic features like CASE, NUM (number), and TENSE are attributes of the functional structure. An attribute can have an atomic symbol, a semantic predicate expression or a feature structure as a value. By means of two special variables, the feature equations in the phrase structure rules dictate the coreference between the feature structures of the nodes of the local tree and the attributes of the functional structure. The functional structure of the mother constituent is indicated by the symbol ‘î’, the functional structure of the daughter constituent, with the symbol ‘↓’. For example, the equation (↑OBJ2)=under the categorial symbol NP in a verb phrase rule means that the functional structure of the noun phrase is coreferent with the value of the attribute OBJ2 in the functional structure. The phrase structure rules of LFG overgenerate structures. The structures must satisfy three global wellformedness constraints which function as filters. (a) The principle of functional uniqueness states that every attribute in a functional structure may possess only one value. (b) The principle of functional completeness states that a functional structure is locally complete when it contains all the governable grammatical functions that its predicate governs. (c) The principle of functional coherence states that in every substructure of the functional structure, all governable grammatical functions are governed by the predicate of the substructure. Subcategorization ensues from the attribute PRED in the lexical entry, in which only the grammatical function of the obligatory and optional complements are specified, not their syntactic category. In LFG many syntactic relations described by transformations in transformational grammar (e.g. those between sentences with transitive verbs and the corresponding sentences with passive, middle, or causative verbs) are produced in the lexicon rather than the syntax. Lexical rules relate the corresponding verb classes and produce the correspondences between the complement position in the PRED attribute. Non-local dependencies, e.g. in wh-questions and topicalization, were originally dealt with by feature transmission. A newer version of LFG treats non-local dependencies through functional uncertainty (see Kaplan and Zaenen 1989). The functional structure of a sentence, especially the predicate expression that is the value of the attribute PRED, is the basis for semantic interpretation. Halvorsen (1983) suggests a semantic component borrowed from Montague grammar. Fenstad et al. (1987) use functional structure for the encoding of situational schemata, feature-based representations of meaning, which can be interpreted by using situation semantics. LFG was used for many descriptions of individual languages, e.g. English (Bresnan 1982), for Warlpiri (Simpson and Bresnan 1983), Chichewa, Japanese, and Serbo-Croatian (Iida et al. 1987). It also serves as the basis for the implementation of numerous computational natural language systems on the computer, e.g. Reyle and Frey (1983), Block and Haugeneder. (1988), and Kaplan and Maxwell (1988).

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Kaplan, R.M. and Z.Zaenen. 1989. Long-distance dependencies, constituent structure, and functional uncertainty. In M.Baltin and A.Kroch (eds), Alternative conceptions of phrase structure. Chicago, IL. 17–42.

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