Halliday & Matthiessen (1999: 106-7, 108):
We could say that the world view that is constructed in this way is (quite reasonably, from our point of view) focussed on humans, with human consciousness occupying a privileged place. Thus typically only humans can project into second-order reality. However, since human consciousness is the locus of semiotic activity, it has the power of interpreting as metaphenomenon that which is manifested by some other, non-conscious symbolic source. Thus while "sensing" (that is, semiotic activity that is unmanifested, like thinking) does require a human senser, saying can be ascribed to a nonhuman as well as to a human sayer (cf. he thinks —> the moon is a balloon vs he says/the book says —> the moon is a balloon. Figure 3-2 shows the relationship between the two orders of metaphenomena and the presence of consciousness in the act of projection.
