Halliday & Matthiessen (1999: 28):
The gateway to semantics is the clause rather than the word. Consequently, grammatical categories will typically be interpreted 'from above', within 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. Systems that are approached 'from above' in this way include:
projection — clause complex: traditionally a form of 'subordination' within clause; reinterpreted as distinction between hypotaxis in clause complex vs. rankshift in clause, laying the foundation for a semantic distinction between reports and facts.transitivity — clause: traditionally a word category, transitive = verb taking object/ intransitive = verb not taking object; reinterpreted as (i) process types (material/ mental/ verbal/ relational) and (ii) an ergative system (middle/ effective) in the clause.tense — group: traditionally a mixture, because the model was taken over from Latin with richer word-rank realisations than English, but more recently in this century often a word category, past/ non-past; reinterpreted (relative to this) as (i) past/ present/ future and (ii) recursive, with secondary tense.
Taking the clause as starting point facilitates the exploration of cryptotypes: the chain of realisation often starts cryptotypically in the clause, whereas the final stages of realisation at word and morpheme rank are more oven — although, as noted in connection with tense and number, the oven marking is seldom the only factor involved.