It is important to recognize that language is a system of units and their relations, because that often serves as our criterion of what material is language and what is not. Only on this basis do we exclude at present the vast and as yet organized fields of expressive modifications (e.g. anger-modulations, intonations of sarcasm, etc.), and of the linguistic differentiae used by particular sections of the community (e.g. characteristic intonations of girls, etc.). All these have conventional phonetic forms and meanings, no less than language proper, and are marked off from language only because we cannot analyze them structurally in the same way.
- Harris (1940), a pag.223