Halliday & Matthiessen (1999: 190):
These primary categories of things represent an ordering of the phenomena of experience. This ordering has to do with their inherent potential for bringing about change: that is, their ability to initiate processes and to affect other participants.
One way of exploring this is by noting which participant roles each category of participant is typically associated with. The critical roles, in this respect, are those of Senser, Sayer and Actor, operating respectively in figures of sensing, saying and doing & happening. When we investigate these, however, we find that the overall categorisation of phenomena that is revealed in this way displays a further dimension of complexity: at the highest level, all phenomena are distributed into two broad experiential realms, the material and the semiotic. This suggests that we should further modify the schema of primary categorisation by splitting it into these two realms as shown in Figure 5-7. This figure also splits the categories of object and abstraction between the two realms.
