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Depression in Zulu: tonal effects of segmental features

Zulu, a Bantu/Nguni tone language spoken in South Africa, exhibits a curious interaction between tone and consonants, in which a specific set of onset consonants is correlated with extreme lowering of an immediately following high (H) or low (L) tone. This extreme lowering often causes realignment of tones and has been called ‘tonal depression’. The triggering consonants are traditionally referred to as ‘depressors’.

While the phenomenon of tonal depression has been found and studied in several Bantu languages, neither the set of depressor consonants nor the mechanism of depression have been satisfactorily characterized. Early attempts to define depressors as a natural class based on a feature like [+ breathy voice] are contradicted by the facts (cf. TKF 1987, GPT 1988). The hypothesis that tonal depression is caused by a L tone associated with an obstruent (Laughren 1981) is inconsistent with standard assumptions about the sonority of tone bearing units (TBUs). Proposals for a tone insertion rule that places an extra L tone on the ‘regular’ tonal tier cannot explain why tonal depression consistently occurs very late in the derivation: H tone distribution initially follows its regular patterns regardless of the presence of depressor consonants, while depressor induced H tone shift is blocked by depressor consonants.

In this paper, I will argue that tonal depression in Zulu warrants the introduction of a new feature pair into the feature geometry. This enhanced feature geometry is not only phonetically motivated, but also provides a straightforward explanation of otherwise puzzling characteristics of tonal depression and its effects in the phonology.

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I am deeply indebted to Marlys Macken for her detailed comments on the many drafts of this paper. Anthony Traill kindly supplied me with literature and gave me invaluable pointers early in the thought process. I thank Tom Purnell for comments on earlier versions and frequent discussions. All errors are, of course, my own.