Phrase Structure Grammars

Phrase structure grammars model the internal structure of a sentence in terms of a hierarchically organized representation. The sentence Every boy has a bike, for instance, is taken to consist of a noun phrase (every boy) and a verb phrase (has a bike), where the former consists of a determiner (every) and a noun (boy), and the latter of a verb (has) and a noun phrase (a bike), which, in turn, consists of a determiner (a) and a noun (bike). The structure is made explicit by labeled bracketing, as in (S (NP (Det every) (N boy)) (VP (V has) (NP (Det a) (N bike)))), or by a tree. Phrase structure grammars were introduced by Noam Chomsky in the 1950s, building on the tradition of Immediate Constituent Analysis in post-Bloomfieldian structuralism. They played a key role in Transformational Grammar (TG) till the late 1960s, mainly as a descriptive device. The shift toward generalization led to a more abstract version, widely known as X-bar syntax, a staple ingredient of generative syntax throughout the 1970s and the 1980s. The introduction of the Minimalist Program in the 1990s led to further abstraction, involving, among others, the virtual elimination of phrase structure rules. In Non-transformational Grammar, which has its origins in the 1970s, phrase structure grammars continue to thrive, especially in Lexical-Functional Grammar (LFG) and Head-Driven Phrase Structure Grammar (HPSG). While phrase structure grammars are mainly used in syntax, they also play a role in other areas of linguistics: they provide a structural backbone for the compositional interpretation of sentences in Semantics and for identifying prosodic units in Phonology. Their role in morphology is a bone of contention: in Transformational Grammar, the smallest units of analysis are morphemes, so that PS grammars extend below the word level. Non-transformational Grammars, by contrast, adopt a lexicalist stance and treat words as syntactic atoms, leaving the expression of sublexical regularities to other devices, such as lexical rules. The Formal Properties of phrase structure grammars have been studied in mathematical linguistics. They play a key role in computational linguistics and Natural Language Processing. Their relevance for the investigation of human language processing is studied in Psycholinguistics.