Functional theories of grammar include a range of functionally based approaches to linguistics, the scientific study of language. The grammar model developed by Simon Dik bears this qualification in its name, functional grammar, as does Michael Halliday's systemic functional grammar.
Role and reference grammar, founded by Robert Van Valin is also considerered a functional theory. A figure in recent linguistic functionalism is Talmy Givón, but his theorising has not been given a unique name.
Dik characterises functional grammar as follows:
In the functional paradigm a language is in the first place conceptualized as an instrument of social interaction among human beings, used with the intention of establishing communicative relationships. Within this paradigm one attempts to reveal the instrumentality of language with respect to what people do and achieve with it in social interaction. A natural language, in other words, is seen as an integrated part of the communicative competence of the natural language user. (2, p. 3)
Because of its emphasis on usage, communicative function, and the social context of language, functional grammar differs significantly from other linguistic theories which stress purely formal approaches to grammar, notably Chomskyan generative grammar. Functional grammar is strongly associated with the school of linguistic typology that takes its lead from the work of Joseph Greenberg.