Martin (1992: 222):
By way of introducing the concessive internals, compare [4:145] and [4:146], the second of which anticipates the challenge in the first.
[4:145] Dinner's ready.— But I'm not hungry.
[4:146] Dinner's ready.But you may not be hungry.— I'm not.
As will be taken up in 4.4.5 below, changing the taxis as far as the realisation of internal relations is concerned helps to focus on their meaning. Paraphrasing the but in [4:145] along these lines produces: 'although you've called me to dinner, I'm not hungry.'; the paraphrase for [4:146] is more elaborate: 'although I've called you to dinner I suspect you might not be hungry and am conceding a possible objection.' Some internal concessives in other words are designed to anticipate challenges.
 In SFL theory, the contrast being exemplified here is between conjunctive relations of extension and enhancement.
- The relation in the first, across speakers, is adversative addition. The meaning is X and conversely Y.
- The relation in the second is concessive condition. The meaning is if P then contrary to expectation Q.
 As the words challenge(s) and objection suggest, Martin's metafunctional perspective has shifted here from the logical (textual in SFL theory) to the interpersonal. Challenging and objecting signal enactments of interpersonal meaning. Conjunctive relations are being interpreted on the basis of the interpersonal meanings of the messages being conjoined.
 There is no change in taxis in these examples because there is no taxis. In each case, the but marks a cohesive — non-structural textual — conjunctive relation. For there to be a tactic relation, the clauses thus related would have to form (a nexus within) a clause complex.
 Bringing meanings into focus is a function of the textual metafunction. Here Martin is describing what he takes to be the logical metafunction.