Halliday & Matthiessen (1999: 190-1):
conscious (prototypically adult human)typifying roles: active participant in figure of sensing [Senser, e.g. do you think so?], of saying [Sayer, e.g. the teacher said.,.] and of doing [Actor: middle, e.g. Pat skipped, or effective, e.g. Chris held the rope].pronoun he/she/they (also I/you); general noun person etc.; number category: count (singular/ plural).has potential for voluntary action [material: doing, including doing to another participant; verbal (semiotic): saying] and conscious processing of all kinds [mental: sensing, including feeling, thinking, intending as well as perceiving].