Halliday & Matthiessen (2014: 660):
A text is thus a unit of meaning – more accurately, a unit in the flow of meaning that is always taking place at the instance pole of the cline of instantiation. How does this semantic unit relate to the units and unit complexes of grammar – the clause (clause complex), the groups (group complexes) and so on? The folk view is that a text consists of clauses (or ‘sentences’); but this is a misleading simplification of a more indirect – but much more flexible and powerful – relationship. A text does not ‘consist of’ clauses (clause complexes) – there is no part-whole or ‘constituency’ relationship between a text and a clause (complex) and there is no single rank scale with text and clause as ranks. Rather a text is realised by clauses (clause complexes), the two being located on different strata – semantics (the stratum of meaning) and lexicogrammar (the stratum of wording) respectively.
Blogger Comments:
It is important to understand (and maintain) the difference between a text as semantic unit, and text as an instance of language. A text as semantic unit is the highest unit on the semantic stratum, and so, realised by the clauses of lexicogrammar. A text as an instance of language is an instance of language as a whole, not just the semantic stratum.