What we have been describing under the ʻideationalʼ heading has been meaning as organization of experience; but there is also a logical aspect to it – language as the expression of certain very general logical relations – and it is this we have to introduce now. The logical component defines complex units the CLAUSE COMPLEX.
- Halliday (1985), a pag.159

[…] A sentence can be interpreted as a CLAUSE COMPLEX: a Head clause together with other clauses that modify it.
- Halliday (1985), a pag.192

We shall assume, therefore, that the notion of ʻclause complexʼ enables us to account in full for the functional organization of sentences. A sentence will be defined, in fact, as a clause complex. The clause complex will be the only grammatical unit which we shall recognize above the clause. Hence there will be no need to bring in the term ʻsentenceʼ as a distinct grammatical category. We can use it simply to refer to the ortographic unit that is contained between full stops. This will avoid ambiguity: a sentence is a costituent of writing, while a clause complex is a costituent of grammar.
- Halliday (1985), a pag.193