Halliday & Matthiessen (1999: 259-60):
Rank shift is not inherently metaphorical. There is a parallel here between rank shift and class shift. In origin, both these could be described as metaphorical semogenic processes: a verb or adjective is metamorphosed into a noun (a shift of class, e.g. strong : strength, lose : loss), a clause is metamorphosed into a group (a shift of rank, e.g. they went bankrupt : their bankruptcy).
But as a synchronic relation neither of these necessarily involves metaphor; there may be no systematic alternation such as there is between a metaphoric and a congruent form. We have already discussed non-metaphorical forms of class shift, under the heading of transcategorisation. Similarly, in the following examples of rank shift, where a clause is rankshifted to function either as Head (1,2) or as Qualifier (3, 4) of a nominal group, no grammatical metaphor is involved.
1. [[Not having a proper job]] made my life unbearable(semantically) non-projected figure as participant(grammatically) clause (as Head of nominal group) functioning (as Agent) in clause structure: "act" type2. [[How they escaped]] was a mystery(semantically) projected figure as participant(grammatically) clause (as Head of nominal group) functioning (as Carrier) in clause structure: "fact" type3. That woman [[(who was) sitting behind the desk]] reminded me of Tracy(semantically) non-projected figure as quality(grammatically) clause functioning as Qualifier of nominal group ("defining relative" clause)4. The idea ([that anyone would visit/ of anyone visiting]] seems incredible(semantically) projected figure as quality(grammatically) clause functioning as Qualifier of nominal group