Martin (1992: 39-40):
The final set of factors to be taken into account when determining speech function are considerations of context. Can you open this window? when inspecting a property is likely to be heard differently than when sitting in a stuffy room. Field, mode, tenor, genre and ideology are all relevant as participating levels of semiosis; it is not possible simply to map speech function directly from 'words on the page'.
 This blurs the distinction between context (the field of property inspection) and material setting (a stuffy room). The context is the semiotic system that is realised by language. In these instances, the speech function realised by the interrogative clause — question or command— varies with the situation being realised in language.
 While field, tenor and mode are metafunctional systems of a level of semiotic systems — the stratum of context — genre, as the name suggests, is a type of semiotic system. A type of x is not a level of x. A type of bird is not a level of bird.
 It is worth clarifying that the four most general speech functions are defined in terms of the cross-classification of giving vs demanding and information vs goods-&-services, and that three of these have congruent realisations in the mood system — the level of wording. Metaphorical renderings can be identified by testing the mood choice against the speech function cross-classification. Congruent and metaphorical renderings realise, and construe, different tenor values at the level of context.