A False Conclusion Invalidly Argued From False Premises

Martin (1992: 447):

This pattern of marked Themes in [4:2] is the dynamic equivalent of the synoptic metaphorical hyper-Themes discussed above. But in spoken mode the marked Themes punctuate rather than predict, annotating the text in episodes as it unfolds rather than scaffolding it as a macro-constituent structure that is in some sense preconceived. Seen in this light hyper-Themes can be interpreted as a further category of textual metaphor: a hyper-Theme is an [sic] metaphorical marked Theme.

Blogger Comment:

The invalidity of this argument can be made more obvious by making the text less opaque.  This can be done by glossing three of the terms used, as follows:

• (metaphorical) hyper-Theme = Topic Sentence (involving nominalisation)
• punctuate = interrupt
• annotate = add notes to a text, giving explanation or comment

Martin's argument now becomes:

This pattern of marked Themes in [4:2] is the dynamic equivalent of the synoptic Topic Sentences involving nominalisation discussed above. But in spoken mode the marked Themes interrupt rather than predict, providing comments on the text in episodes as it unfolds rather than scaffolding it as a macro-constituent structure that is in some sense preconceived. Seen in this light Topic Sentences can be interpreted as a further category of textual metaphor: a Topic Sentence is a metaphorical marked Theme.

The argument, then, is as follows.

Because

• marked topical Themes interrupting and providing comments on a spoken text (in episodes as it unfolds) 
• are the (dynamic) equivalent of 
• (synoptic) Topic sentences involving nominalisations scaffolding a written text (as a macro-constituent structure),

it logically follows that

• a Topic sentence involving nominalisation 
• is a metaphorical 
• marked Theme.

Leaving aside the false claims of the premises — including the claim that marked topical Themes provide comments on ("annotate") spoken texts — the validity of the argument rests on the assumption that the written counterpart of a spoken language feature constitutes textual grammatical metaphor.

This, of course, is not consistent with the notion of grammatical metaphor.

Grammatical metaphor is the incongruent grammatical realisation of semantic selections.  It is, in the first instance, an incongruent relation between the two levels of content: semantics (meaning) and lexicogrammar (wording).

Considering now the conclusion of the argument, to say that 'a hyper-Theme is a metaphorical marked Theme' is to say that:

• a Topic Sentence is the metaphorical realisation of what would be congruently realised as a marked topical Theme of a clause.

That is to say, an unspecified semantic choice (textual metafunction) is realised 

• congruently in the grammar as a marked topical Theme, and 
• incongruently in the grammar as a Topic Sentence, which is itself a type of graphological unit construed as part of a discourse semantic interaction pattern.

Conclusion:

Martin's argument proceeds from false premises, is invalidated by a false assumption, and ends with a false (and internally inconsistent) conclusion.