Halliday (2008: 188-9):
Semiotic phenomena — the patterns that evolve in a system that creates meaning — have this property: that they depend on the brain’s ability to adopt a multiple perspective. Meaning has to be at the same time both process and entity; both potential and actual; both general and particular. And since the only strategy we have for describing and explaining a system like this is that of refracting it through another cycle of meaning — a scientific theory — we find it difficult to transcend these awkward disjunctions.