Martin (1992: 500):
At the same time however it is important to note the uncertainty in Halliday's writing as to whether mode is meant to cover genre. At times this connection is explicitly made (e.g. "mode covers roughly Hymes' channel, key and genre" 1978: 62). Elsewhere Halliday would appear to disassociate genre from any one contextual variable (e.g. In the most general terms there are two other components of texture. One is the textual structure that is internal to the sentence: the organisation of the sentence and its parts in a way which relates it to its environment. The other is the 'macrostructure' of the text, that establishes it as a text of a particular kind — conversation, narrative, lyric, commercial correspondence and so on" Halliday & Hasan 1976: 324).
There is no uncertainty on this matter in the quotes presented above. The first quote is about the textual metafunction at the level of context, whereas the second quote is about the textual metafunction at the level of semantics. That is, each quote is concerned with a different level of symbolic abstraction.
In the first quote, rhetorical mode is identified with Hymes' notion of genre, which, in SFL theory, is the part language plays in the situation type.
The second quote, on the other hand, is concerned with the textual structure (semantics) of a text type ("genre") that realises a particular rhetorical mode (situation type).
The dimensions in play here are
- stratification: context versus semantics, and
- instantiation: situation type as subpotential of context, and text type as subpotential of semantics.