Halliday & Matthiessen (1999: 467):
In the participant-organising perspective, it is the nature of the participants involved in the process that determines the different process types. Relevant variables include the following:
1. Is some participant created, brought into existence, by the process?
2. Is some participant restricted to conscious being?
3. Can some participant be a metathing as well as a thing?
4. Is the process directed towards some participant?
5. Does the process benefit some participant?
6. Does the process occur spontaneously or does it need an input of energy?
7. Does the process affect some participant materially or does it impinge on its consciousness?
8. Is the process symmetric?
9. Is the process reflexive?