Functional grammar

In the functional paradigm a language is in the first place conceptualized as an instrument of social interaction among human beeings, used with the intention of establishing communicative relationships. Within this paradigm one attempts to reveal the instrumentatlity 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)

Reference:

1. Functional grammar home page (http://www.functionalgrammar.com/)
2. The Theory of Functional Grammar (Part I: The Structure of the clause), 1989