Halliday & Matthiessen (2014: 713-4):
As we have seen, the ideational metafunction is a resource for construing our experience of the world that lies around us and inside us. In the congruent mode, the grammar construes sequences (of figures), figures and elements as the basic phenomena of experience. In the metaphorical mode, the model is enriched through combinations of these categories: in addition to the congruent categories, we now also have metaphorical combinations of categories – sequences construed as figures, figures construed as elements, and so on. These combinations open up new meaning potential. For example, in a sequence, there is a temporally invariant logico-semantic relation such as cause, but in a sequence construed as a figure, this relation is typically construed as a process. Unlike a logical relation, a process is construed as unfolding through time, and in the grammar of the verbal group it is marked for tense or modality.