Martin (1992: 518):
The same MOOD opposition is relevant to the genre-structured texts, distinguishing hortatory ('so change your ways') from analytical ('so this is how things are') exposition.
This purports to cross-classify exposition texts, hortatory vs analytical, according to (Martin's) mode and mood: imperative vs indicative, respectively. However, this misrepresents the distinction between these two types of exposition, both of which involve the presentation of arguments. The text structure (semantics) that realises a hortatory exposition (context: mode) is typically:
whereas the text structure (semantics) that realises an analytical exposition (context: mode) is typically:
The function of a hortatory exposition is to explain to the reader that something should or should not happen or be done — not to command the reader — whereas the function of an analytical exposition is a to persuade the reader that an idea is important.
The fundamental confusion here is that the discussion is presented as theorising mode, the systems of the textual metafunction at the level of context. Here, instead, the discussion is concerned with the interpersonal dimension of linguistic content — semantics (speech function) and lexicogrammar (mood) — of registers. The confusion is thus simultaneously along three theoretical dimensions: stratification, metafunction and instantiation.