Halliday & Matthiessen (1999: 263):
In metaphor … the phenomenon is reconstrued as another category; what is being exploited is the potential that arises — but only after the categories have first been construed as distinct; not otherwise — of treating every phenomenon in more ways than one. In this process the original interpretation is not supplanted; it is combined with the new one into a more complex whole.
Halliday & Matthiessen (1999: 283):
… we have shown that the metaphorical version is not simply a meaningless (ie synonymous) variant of some congruent form; it is ‘junctional’ — that is, it embodies semantic features deriving from its own lexicogrammatical properties.