Grammatical Metaphor

Halliday & Matthiessen (1999: 227):

We have seen that sequences, figures, and elements are congruently realised in the grammar as follows: 

	clause complex	clause	group
sequence	ü
figure		ü
element			ü

But these resources may be expanded by taking up further options in realisation; for example, sequences may alternatively be realised by clauses and even groups.  This what we refer to as grammatical metaphor.  Grammatical metaphor expands the semantic potential of the system.