What makes learning possible is that the coding imposed by the mother tongue corresponds to a possible mode of perception and interpretation of the e… - Michael Halliday

[... language, as an example of a semiotic system, contains all four levels of organization as follows:] First, it is transmitted physically, by sound waves traveling through the air; secondly, it is produced and received biologically, by the human brain and its associated organs of speech and hearing; thirdly it is exchanged socially, in contexts set up and defined by the social structure; and fourthly it is organized semiotically as a system of meanings

Any text in spoken English is organized into what may be called 'information units'. (...) this is not determined (...) by constituent structure. Rather could it be said that the distribution of information specifies a distinct structure on a different plan. (...) Information structure is realized phonologically by 'tonality', the distribution of the text into tone groups.

We should not, perhaps, take it for granted that a description in terms of a formalised model, which has certain properties lacking in those derived from models of another kind, will necessarily be the best description for all of the very diverse purposes for which the descriptions of languages are needed. In assessing the value of a description, it is reasonable to ask whether it has proved useful for the purposes for which it was intended.