Halliday (2008: 146):
In it’s ideational guise, the grammar is making sense out of the diversity of human experience by construing it into discrete quanta, which we call “figures”. Each figure is in turn construed as a configuration of elements, which are of a small number of different types. If we take English as our exemplar (but English is very typical in this respect), the figure is made up of a process of some kind, a small number of entities playing particular parts in that process, and perhaps one or two circumstantial elements surrounding it.