Halliday & Matthiessen (1999: 28):
[Our move into semantics from grammar also differs from the traditional in that] The gateway to semantics is the clause rather than the word. Consequently, grammatical categories will typically be interpreted ‘from above’, with their context in the clause or the group, rather than ‘from below’ within their context in the word. This has rather far-reaching consequences for the understanding of the semantic systems realised by the grammar.