Misrepresenting Grammatical Structure As Lexical Relations

Martin & Rose (2007: 87-88):

Tutu uses contrasts frequently to mount his argument for reconciliation over retribution. For example, he uses an antonym in his Thesis to emphasise the significance of the debate:

So is amnesty being given at the cost of justice being done? This is not a frivolous question, but a very serious issue, one which challenges the integrity of the entire Truth and Reconciliation process.

Blogger Comments:

To be clear, the antonyms in this instance are frivolous and serious.  In SFL theory, the relation constitutes an example of lexical cohesion, a non-structural resource of the textual metafunction at the level of lexicogrammar.

Here Martin & Rose misrepresent the nominal groups a frivolous question and a very serious issue as lexical items and misinterpret the relation between them as construing experiential meaning.

The experiential meaning that the authors attribute to a lexical relation is actually construed by the ideational grammar as an extending replacive relation in a nominal group nexus realising an Attribute:

this	is	not a frivolous question, but a very serious issue
Carrier	Process: attributive	Attribute

not a frivolous question	but a very serious issue
1	+ 2

Moreover, unknown to Martin & Rose, Tutu here is using the rhetorical device known antithesis, wherein two opposite ideas are put together in a sentence to achieve a contrasting effect.