The child knows what language is because he knows what language does. The determining elements in the young child’s experience are the successful demands on language that he himself has made, the particular needs that have been satisfied by language for him. He has used language in many ways – for the satisfaction of material and intellectual needs, for the mediation of personal relationships, the expression of feelings and so on. Language in all these uses has come within his own direct experience, and because of this he is subconsciously aware that language has many functions that affect him personally. Language is, for the child, a rich and adaptable instrument for the realization of his intensions; there is hardly any limit to what he can do with it.
- Halliday (1973), a pag.10

Language is itself a potential: it is the totality of what the speaker can do.
- Halliday (1973), a pag.110

Language is used to define and consolidate the group, to include and to exclude, showing who is ʻone of usʼ and who is not; to impose status, and to contest status that is imposed; and humour, ridicule, deception, persuasion, all the forensic and theatrical arts of language are brought into play.
- Halliday (1973), a pag.13-14

The internal organization of natural language can best be explained in the light of the social functions which language has evolved to serve. Language is as it is because of what it has to do.
- Halliday (1973), a pag.34

If we regard language as social behaviour, therefore, this means that we are treating it as a form of behaviour 'potential'. It is what the speaker can do.
- Halliday (1973), a pag.51

Language is as it is because of its function in the social structure, and the organization of behavioural meanings should give some insight into its social foundations.
- Halliday (1973), a pag.65

We shall define language as ʻmeaning potentialʼ: that is, as sets of options, or alternatives, in meaning, that are available to the speaker-hearer. At each of the levels that make up the linguistic coding system, we can identify sets of options representing what the speaker ʻcan doʼ at that level. When we refer to grammar, or to phonology, each of these can be thought of as range of strategies, with accompanying tactics of structure formation.
- Halliday (1973), a pag.72

Language is the primary means for the transmission of culture from one generation to the next […].
- Halliday (1973), a pag.8