Halliday & Matthiessen (1999: 599):
These two models move away from the folk model in two directions. (i) They reinterpret figures of sensing as figures of doing or being–&–having; that is, they interpret mental phenomena in material terms. … (ii) They emphasise motivation as an important unconscious psychological factor; thus they introduce unconsciousness in the workings of the human mind. In the systems of process types in the grammar, there is no ‘unconscious’ type of sensing distinct from the conscious ones that can project ideas.