Halliday & Matthiessen (1999: 288, 289):
The correspondence that is construed through grammatical metaphor is an elaborating relationship: an identity is set up between two patterns, a sequence and a figure, a figure and a participant, and so on. In this identity, the metaphorical term is the Token' and the congruent term is the 'Value': 'engine failure' stands for (means, represents) 'engines fail'. This is the 'core' meaning of the elaborating relation; but it also covers the senses of 'summarise', 'distil' — the metaphor may 'distil' congruent meanings that have accumulated in the text. The identity holds between the two configurations as a whole; but, as our representations indicate, the components of the configurations are also mapped one on to another: see Figure 6-16.
