Halliday & Matthiessen (1999: 153):
But these "impacting" figures of sensing and saying are only submotifs within these two overall types. The general motif of figures of sensing is 'conscious processing'; that of figures of saying is 'symbolic processing'. And in figures of being, where we might characterise the general motif as 'relational ordering', there is no trace of a submotif of impacting at all.