Martin (1990: 216):
Within opposition, the distinction is between retraction and contrast. With retraction, a "straw message" is set up, often involving a negative realisation of some kind; this message is then retracted and another put in its place as in [4:131]. With contrast the first message is not set up rhetorically in order to be opposed; internal contrastive relations may select the correlative realisation on the one hand…one the other (hand).
DIFFERENCE:OPPOSITION:RETRACTION[4:131] It would certainly be wrong to dismiss the results of such asocial linguistics as simply false.Rather, we can see it as incomplete, in the same way that linguists of the 1970s find earlier grammars incomplete because they had little to say about syntax and even less about semantics or pragmatics.
DIFFERENCE:OPPOSITION:CONTRAST[4:132] On the one hand we could view such grammars as false, or at least as politically irresponsible.On the other it might be preferable to see them as incomplete; this is the more comforting liberal view.
In SFL theory, the conjunctive relation in the first text is corrective clarification, a type of elaboration, whereas the conjunctive relation in the second text is adversative addition, a type of extension. See Halliday & Matthiessen (2004: 542).
Here this opposition of elaborating vs extending conjunction is misconstrued as opposing subtypes of enhancement (difference as a type of comparative relation, misconstrued as internal).