Halliday & Matthiessen (1999: 262-3):
At the same time, a further distinction has evolved between two kinds of logical-semantic relation:(i) a relation 'in rebus' between two experiential events,(ii) a relation 'in verbis between two stages in the discourse;e.g.(i) Political pressures brought about his downfall. Major changes ensued.(ii) This section illustrates the main argument. Further discussion follows.
These correspond respectively to the 'external' and 'internal' types of conjunctive relations in cohesion (Halliday & Hasan, 1976: Ch. 5).