Halliday & Matthiessen (2014: 432-3):
Circumstances augment the configuration of process + participants in the clause in terms of either projection or expansion. These two types of relation correspond, in turn, to different process types: projection corresponds to verbal and mental clauses, and expansion corresponds to relational clauses. Projection and expansion are also manifested as the logico-semantic relations that link clauses together to form clause complexes. The manifestations of projection and expansion in the clause and the clause complex are set out in Table 7-2.
