Halliday & Matthiessen (1999: 146-7):
One participant enhances along a circumstantial dimension of time, space, cause, condition and the like. … Thus enhancing figures may be used to construe arrangements or orderings in space or time, such as chronologies, maps or structures. … Enhancing figures construing temporal and causal ordering play an important rôle in constructing knowledge in a metaphorical mode …