Halliday & Matthiessen (1999: 16):
We are also constructing meaning out of the grammar. But there are two significant differences.
(i) One is that we are not starting from the word, but from larger units of grammatical organisation: clauses and clause complexes (sentences) — the largest units, in fact, that are constructed on grammatical principles.
(ii) The other is that we are starting not from the overt categories and markers of the grammar, like case and case inflexions, but from the often covert, cryptogrammatical relations that are less immediately accessible to conscious reflection yet constitute the real foundation on which the grammar construes the world of our experience.