So, why are we using a figure, rather than, say, some other order of phenomenal complexity such as the element or sequence? Because the key to the construal of experience is the perception of change, and the grammar — the central processing unit of language [Halliday & Matthiessen (2004: 21)] — construes a quantum of change as a figure [Halliday & Matthiessen (1999: 213)], which is congruently realised by a clause — the central processing unit of the grammar [Halliday & Matthiessen (2004: 10)].
And, unlike an element, for example, ‘a figure embodies both analysis and synthesis of our experience of the world: an analysis into component parts, and a synthesis of these parts into a configuration’ [Halliday & Matthiessen (1999: 165)].