Functional approaches to language have expanded in many directions since the development of the notion of constitutive factor. From the analytic philosophy of language (Austin, Strawson, Urmson, Searle) came the notion of a `speech act' with `locutionary, illocutionary, and perlocutionary force' in dialogue; from ethnomethodology in empirical sociology came the notion of conversation analysis, which developed into further varities of discourse analysis and dialogue analysis in general.
Given such an array of functions of language, and of the constituents of discourse, the simple three-dimensional model of language variation has come to appear inadequate. The functional dimension alone may be divided into a series of further dimensions, down to contextual variation at fine levels of analysis such as `fast speech phenomena' and `hypercorrection'.
The most comprehensive theory of the interconnections between the dimensions of language variation has been given by Labov.
Task: Find the main features of `speech act theory', of `conversion analysis' (and related methods), and of Labov's approach to relating contextual styles, social variation and language change.