Some phonetic features occur regularly in particular situations: in sufficiently stratified societies there are recognizable differences between the way a, say, upper middle class woman talks to a social equal and to a servant ( even when the utterance is otherwise identical). Other features may be present in all the speech of a particular person during several years of his life, witness the fact that we can recognize a person by his voice. Still others characterize the members of a particular age group, social class, etc., witness the fact that in certain cases we can tell the class or age group of a speaker before we see him. All such features extend over more than single utterances, and can be described as superposed upon the utterance-length contours […]. In incidence and meaning, these features border closely upon gesture and are of importance to any consideration of how language occurs in social interaction. In their representation of speech, these features can be distinguished from the segments and contours which have been treated in these procedures only by the fact that they extend over more than single utterances.
- Harris (1951), a pag.55