Halliday & Matthiessen (1999: 134, 136):
We have characterised the distinctions among the different types of figure in semantic terms. Let us now relate them to the grammar of TRANSITIVITY — the ideational grammar of the clause where the semantics of figures is construed. The different semantic types, sensing, saying, doing & happening and being & having are realised in the grammar of transitivity as shown in Figure 4-4. Thus doing & happening are realised as material clauses, sensing as mental ones, saying as verbal ones, and being (at, etc.) & having as relational clauses. The different process types are not signalled overtly in the grammar; they are covert or cryptotypic categories and emerge only when we consider their reactances, shown in italics in Figure 4-4.
