Halliday & Matthiessen (2004: 639):
… grammatical metaphor within the ideational metafunction involves a ‘re-mapping’ between sequences, figures and elements in the semantics and clause nexuses, clauses and groups in the grammar. … In the metaphorical mode, the whole set of mappings seems to be shifted ‘downwards’: a sequence is realised by a clause, a figure is realised by a group, and an element is realised by a word.