Martin (1992: 389):
The other main difference between English Text and Cohesion in English has to do with the recognition of NEGOTIATION as a linguistic text forming resource. Halliday and Hasan treat this system as an aspect of the "macro-structure" of text, alongside generic structure — as a feature of register rather than of language (1976: 324 & 327). Halliday's (1984) interpretation of SPEECH FUNCTION as the semantics of MOOD however is preferred here.
 In SFL theory, the text forming resources are those of the textual metafunction. Negotiation, on the other hand, is presented as a system of the interpersonal metafunction.
 Halliday & Hasan (1976: 324, 326-7) are concerned with the textual metafunction — not an interpersonal system of negotiation. They cite the work of Sacks and Schegloff on adjacency pairs to illustrate their point that 'every genre has its own discourse structure', even casual conversation. Such a macrostructure is the one of three components of texture, the other two being non-structural cohesion and structural theme and information.
 This is manifestly untrue in two respects. Firstly, Halliday & Hasan (1976: 324, 326-7) do not describe the macrostructure of a text 'as a feature of register rather than of language'. Secondly, the opposition of register vs language is a nonsense, given that register is defined as a functional variety of language.
 These are not two alternative views of the same phenomenon. The macrostructure of the text is a manifestation of the textual metafunction, and varies according to the mode being realised. Speech function, on the other hand, is a system of the interpersonal metafunction, at the level of semantics.