Halliday & Matthiessen (1999: 577):
We have shown how the system of the ideation base construes consciousness: as conscious processing by a conscious being. Conscious processing can create a higher-order world of ideas (or, as we would say, meanings), comparable in certain respects to Popper's World 3; this defines the essential distinction between projection and expansion as ways of relating one figure to another. Conscious processes themselves appear as the central figures in the construal of experience, and they are pivotal in differentiating among the various types of participant. This folk model is constituted in innumerable encounters in the course of casual conversation; and it is instantiated again and again in contexts of everyday life.
Conscious processes are of two kinds: sensing, and saying. Since what we are exploring here is the modelling of "mind", our concern in the first instance will be with sensing.