Martin & Rose (2007: 124):
The basic options for comparison are similarity versus difference. Perhaps the most common kind of comparison is to contrast two clauses as different, using but:
This is not a frivolous question, but a very serious issue.
Here Tutu contrasts two abstract things, a question and an issue. There is a lexical contrast between their qualities - frivolous versus very serious - and this contrast is made explicit with but. The particular type of difference here is opposition: frivolous and serious realise opposite experiential meanings. But is used in paratactic relations, and opposition can also be realised in hypotactic relations with whereas, while:
Whereas this is a simple question, it is a very serious issue.
Blogger Comments:
[1] To be clear, in SFL Theory, the logical meaning of comparison is 'N is like M', and it is marked by items such as and + similarly; (and) so, thus as, as if, like, the way like (Halliday & Matthiessen 2014: 477). Comparison is a subtype of enhancement.
[2] To be clear, in SFL theory, the logical meaning 'not X but Y' is termed replacive variation, and it is marked by such items as but not; not ... but, instead of, rather than (Halliday & Matthiessen 2014: 471). Replacive variation is a subtype of extension.
Given that Martin & Rose distinguish 'opposite' (i.e. 'adversative' in SFL) from 'replacing' ('instead of'), their analysis of this relation as 'opposite' rather than 'replacing' is even inconsistent with the distinctions of their own model.
[3] To be clear, the relation here obtains between nominal groups, not clauses, which is consistent with the authors' discussion of the elements that are contrasted.
this
|
is
|
not a frivolous question but a very serious issue
|
Carrier
|
Process: attributive
|
Attribute
|
Subject
|
Finite
|
Predicator
|
Complement
|
Mood
|
Residue
|
not
|
a frivolous question
|
but
|
a very serious issue
|
|
1
|
|
+ 2
|
[4] To be clear, in SFL theory, the logical meaning 'X and conversely Y' is termed adversative addition, and it is marked by such items as but, (and) yet while, whereas (Halliday & Matthiessen 2014: 471). Adversative addition is a subtype of extension.
That is, Martin & Rose here misunderstand adversative addition (extension), on the grammatical stratum, as a subtype of comparison (enhancement) and rebrand their misunderstanding as 'opposite', on the discourse semantic stratum.