There are various ways of describing orthographic costituents in English, ranging from that of sentence – word – letter, which is perhaps the simplest one that will work at all, to that of paragraph – sentence – colon unit – comma unit – word – letter, which is more complex but also accounts for more of the facts. All these would be possible representations of the CONSTITUENT STRUCTURE of a written text.
- Halliday (1985), a pag.3

Another form of constituent structure is that which we find in verse. A poem, typically, consists of stanzas, which consist of lines, which consist of feet, which consist of syllables.
- Halliday (1985), a pag.5

Costituent structure in language is only a mechanism for the organization and expression of meaning; and even in this respect it does not do everything, nor do the various different modes of meaning depend on it to the same degree. Nevertheless it is an important link in the chain of grammatical interpretation, and a useful point of departure from which to begin to explore.
- Halliday (1985), a pag.18