Halliday & Matthiessen (1999: 6-7):
But this closeness of fit between the semantics (i.e. the meaning) and the grammar does not mean that our grammatics can take over the semantic domain. Adopting a functional approach enables us to extend the domain of grammar in significant ways in the direction of semantics — not thereby reducing the scope of the semantics but rather enabling us to investigate how experience is construed in semantic terms …