A functional grammar is one which seeks to derive syntactic structures from the functions which language is said to perform. All syntactic analyses take some account of functional categories. Terms such as subject and object, for example, are of this type. Functional grammar, however, attempts to discriminate, with a greater degree of delicacy, between different types of subjects and objects and relate these to semantic possibilities within the language. In essence, the development of this kind of grammar was a reaction to the more abstract approaches associated with Chomskyan Transformational Grammar.
Functional approaches vary somewhat in the terminology and procedures they adopt. One of the most influential of such approaches is that of the British linguist Michael Halliday (13 April 1925 – 15 April 2018). His model of the language is sometimes called systemic grammar. In simple terms this means that he sees language as a semantic system, i.e. a system for expressing meanings. At every point of the system a user is offered a series of choices which are both syntactic and semantic. The context within which these choices are made consists of three overarching functions which language is said to fulfil:
(i) the ideational function: the use we make of language to conceptualize the world. This function emphasizes language as an instrument of thought, a symbolic code, with which we represent the world to ourselves.
(ii) the interpersonal function: the use we make of language as a personal medium. This function emphasizes language as an instrument of transaction by which we represent ourselves to others.
(iii) the textual function: the use we make of language to form texts, whether spoken or written. This function emphasizes language as an instrument of communication with which we construct cohesive and coherent sequences.
According to Halliday, these functions relate to three central purposes which govern the form which clauses take. Clauses act as a representation (ideational function), an exchange (inter- personal function), and a message (textual function)..