Halliday & Matthiessen (1999: 262):
These two syndromes [see previous post] — really variants of a single syndrome — define the type of clause that might well be considered as the favourite type of modern scientific English.
The metaphorical 'things' are packaged processes or qualities that have thematic or informational value in the text, construed as Theme in the clause or New in the information unit (N-Rheme in the clause: see Fries, 1992).
The metaphorical 'process' is one of the typical semantic relations that link figures into a sequence: 'cause* & 'time' are the prototypical relations in question, but in modern writing 'identity' has tended to take over as the central type — often by a further metaphorical step whereby causes becomes is the cause of, results becomes is the result of.