Martin (1992: 501):
Overall it would appear that "rhetorical purpose" is the wild card in contextual description, being variously categorised under field (Halliday 1965), tenor (Gregory 1967), mode (Halliday 1978, 1985/1989) and as a separate contextual variable in its own right (Firth 1950 — effects, Ure & Ellis 1977 — rôle, Fawcett 1980 — pragmatic purpose). The main reason for this is that purpose is difficult to associate with any one metafunctional component of the lexicogrammar or discourse semantics. The effect of a text is the result of all components of its meaning. This makes associating the notion of rhetorical purpose with Bakhtin's more global notion of speech genres an attractive one (cf. Gregory 1982).
 The introduction of the word 'purpose' here is misleading. It is falsely presented as a common feature of the various models of context, despite it being restricted to just one (Fawcett 1980). This unwarranted fudge invalidates Martin's argument.
 Here purpose is not distinguished from effect. This confuses two types of cause: purpose and result. The meaning of purpose is 'because intention Q, so action P', whereas the meaning of result is 'because P so result Q'. This confusion also invalidates Martin's argument.
 Martin's main confusion here is between mode, the rôle played by language, and genre a type of text. This is a confusion of stratification (mode is a dimension of the context stratum) with instantiation (a genre is a subpotential of language). The confusion arises from not distinguishing text types from the contextual features — such as mode: narrative — by which they are identified.