Halliday (2008: 45, 48):
Ideationally, the lexicogrammar sorts out the complex world of our surroundings, including the part that consists of our own bodies, our own “selves”. But the things that surround us, and impinge on us, are immense varied and complex. There are particular things; these have to be sorted into classes, by selecting, out of the innumerable ways in which one thing can be like one another, those analogies that seem to be significant. The classes, in turn, are sorted into classes of classes, or taxonomies. But the critical factor in the way things impinge upon us is that of change. As well as things, there are happenings, which give the things their value; the particular happenings also have to be sorted into their classes, but in addition to this they have to be located in the matrix of space and time. At the same time, however, both things and happenings display certain very general features, properties which can be abstracted out of their particulars and construed as features of whole classes of phenomena, or even of all. All happenings have several “moments” in time; all things have certain qualities or quantities; and so on.