Halliday & Matthiessen (1999: 315):
One major source of this kind of elasticity is the manifestation of the very general semantic types of projection & expansion throughout the ideation base. In English, as we have shown, we find them manifested both logically as relations and experientially as elements within figures:[i] logical manifestation:as relations between figures in the construal of sequences (realised by clause complexes);as relations between processes in the construal of figures (realised by verbal group complexes);[ii] experiential manifestation:as circumstances within figures (realised by prepositional phrases or adverbial groups);as circumstantial processes within figures of being & having (realised by relational clauses);as non-nuclear participants within figures, i.e., participants other than Medium — Agent, Beneficiary, Range (realised by nominal groups with or without a preposition).