Halliday & Matthiessen (2004: 537):
We can make a distinction between conjunction and the three other resources of cohesion. As we have seen, conjunction is concerned with rhetorical transitions — transitions between whole ‘messages’, or even message complexes. Conjunction indicates the relations through which such textual transitions are created. In contrast, the other cohesive resources are concerned with textual status — statuses having to do with how ‘components’ of messages are processed as information.