Givón, Talmy (2001). Syntax. Volume I. Amsterdam/Philadelphia: John Benjamins Publishing Company.
Chapter 1 The functional approach to language and the typological approach to grammar
What is functionalism? Hallidays's [1973: 7] answer, according to Givón (2001: 2): "...A functional approach to language means, first of all, investigating how language is used: trying to find out what are the purposes that language serves for us, and how we are able to achieve these purposes through speaking and listening, reading and writing. But it also means more than this. It means seeking to explain the nature of language in functional terms: seeing whether language itself has been shaped by use, and if so, in what ways — how the form of language has been determined by the function it has evolved to serve..."