Halliday & Matthiessen (1999: 193-4):
The general picture we are suggesting, then, is that it is in the category of thing that the grammar captures to the greatest measure the complexity of the elemental phenomena of human experience. Put together with the different types of figure, which construe the complexity of goings-on upon the broad foundational categories of doing, sensing, saying and being, the different types of participant we have sketched in here foreground the dual nature of experience as being at once both material and semiotic — a world that is constituted out of the interaction between entities and meanings. On each of these dimensions there is a progression from things that are most like to things that are least like ourselves. The grammar imposes a categorisation that is compromising, fluid, indeterminate and constantly in process of change, along with changes in the human condition and in the interaction of humans with their environment. Yet it is also strong enough to bear and carry forward this wealth of often conflicting experience, and transmit it over and over again from one generation of human beings to the next