Theory & the tone unit
DI views intonation as discoursal (not grammatical, not attitudinal) in function. ‘The significance of intonation is related to the function of the utterance as an existentially appropriate contribution to an interactive discourse’ (Brazil 1984:46). ‘By making a choice in any of the intonation systems … a speaker makes some kind of assumption about what he/she takes, for present purposes, to be the state of understanding between him/her and a hearer’ (Brazil 1997:132). Speakers thus make intonation choices according to their perception of the understandings they share with their hearers: these understandings relate to their shared biographies, and to the purposes of their talk in a particular context. Although syntax and intonation do have a relationship in purpose-driven talk (Brazil, 1995), they are regarded as being separate areas of choice. Thus DI holds that there is no ‘normal’ relationship between tone units and clauses.
‘Discoursal in function, not grammatical, not attitudinal’
The tone unit, prominence, tone, key and termination
DI is concerned with the speakers’ moment-by-moment context-referenced choices. It recognises four systems of speaker choice: prominence, tone, key, and termination.Each of these systems adds an increment of interpersonal meaning to the discourse between speaker and hearer(s). The choices made in these systems occur in the domain of the tone unit.
The tone unit
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DI considers that the majority of speech can be divided into units which have either one or two prominences. The two-prominence tone-unit (known as the ‘maximal’) is the typical case: the first prominence (the onset) is non-tonic, the second prominence is tonic, the location of the tone. Unlike other descriptions of intonation, DI does not attribute any significance to the location of boundaries. The tone-unit ends somewhere between the occurrence of a tone, and the onset prominence of the following tone-unit. The example below shows a double-prominence tone unit – click on the speaker icon to hear it.
You can hear this unit in Chapter 5 of Streaming Speech, British and Irish version. In both the British/Irish version, and the American/Canadian version, Chapter 10 contains an intensive training course in using Discourse Intonation to analyse recordings for teaching purposes.