Rank Shift As An Alternative To Metaphorical Class Shift

Halliday & Matthiessen (1999: 261):

… we find that rank shift sometimes operates as an alternative to class shift of this metaphorical kind. In examples A-1 and A-2, there is metaphorical class shift:

A-1 a cow is a ruminating quadruped [verb: adjective; process => quality]

A-2 your escape was a miracle [verb: noun; process => thing]

In B-1 and B-2, on the other hand, there is rank shift but no class shift; these are the agnate congruent forms:

B-1 a cow is a quadruped that chews the cud/ that ruminates

B-2 it was a miracle how/that you got away/ you escaped

Here 'ruminate' and 'escape' remain as process, without shifting in class. This now helps to explain the meaning of forms such as C-1 and C-2:

C-1 a cow is a cud-chewing quadruped

C-2 it was a miracle you/your getting away

These represent a kind of semantic compromise, a means of having it both ways. The junction is now as it were symmetrical, with the time line removed, so that 'chew + cud', 'you + escape' are simultaneously both figures and (parts of) elements. What the grammar is construing here is an exchange of functions without shifting class; the figure takes on a special kind of clausal structure which conserves the transitivity relations.