Halliday & Matthiessen (1999: 618):
… the ontogenetic perspective shows that in fact our experience is being ongoingly reconstrued and recategorised as we grow from infancy to maturity. This is the outcome of processes taking place in human history — evolutionary events that are at once both material and semiotic, and that cannot be reduced to either purely physical processes driven by technology or purely discursive processes driven by ideology.