Halliday & Matthiessen (1999: 241):
The metaphors we are considering here are in fact all shifts within the ideational realm — from sequence to figure, from figure to participant, and so on — and their primary effect is ideational. They constitute a resource for reconstruing experience along certain lines, redeploying the same categories that have evolved in the congruent mode of construing experience.Thus when experience of a quantum of change has been construed as a figure consisting of 'atomic nucleus + absorb + energy', it can be reconstrued as if it was a participant: 'absorption (+ of energy) (+ by atomic nucleus)'. Here the process element of the figure is reconstrued as a thing; and the participants involved in that process are reconstrued as qualities of that thing. Since they are qualities, they are no longer "obligatory"; like any other thing, 'absorption' need not be further specified by reference to qualities.The metaphoric shift does not mean that the natural relationship between meaning and wording is destroyed; rather, this relationship is extended further when new domains of realisation are opened up to semantic categories through metaphor. The shift does however create a greater distance from the everyday experience; the metaphorical mode of construal makes it possible to recast that everyday experience, retaining only certain features from the congruent wording but adding others that it did not include.