Halliday & Matthiessen (1999: 241):
Ideationally, grammatical metaphor is a resource for reconstruing experience so that, alongside congruent configurations, we also have alternative metaphorical ones. At the same time, these different configurations map onto different textual patterns. For example, a figure maps onto a message; but a participant maps onto part of a message, so that a figure construed as if it was a participant can be given a textual status within that message.