The tonal morphology of the potential in Coatec Zapotec (Di′zhke′)

While the phenomenon of tonogenesis is well represented in the literature, diachronic tone change in already-tonal languages has received less attention. This paper considers two types of tonal morphology used to mark the “potential” inflectional category on verbs in Coatec Zapotec (aka Di′zhke′). Some verbs are marked with upstep. Coatec upstepped tones are emergent tonal contrasts that are developing out of high register allotones which assimilated to a historical high tone on a now-deleted preceding syllable. Other verbs display patterns of tone ablaut such that a verb with underlying low or falling tone surfaces with high or rising in the potential. Both upstep and tone ablaut in Coatec can be traced to an earlier floating high tone that could dock onto different syllables according to a set of ranked constraints. Using a combination of internal and comparative reconstruction, details of the earlier tonal system are revealed. This is the first published treatment of Proto-Zapotec tone since Swadesh (1947) and the first paper to address tone in Proto-Zapotecan and Proto Core Zapotec. *ʔ is revealed to have been a consonant through the Core Zapotec period, suggesting that the complex systems of phonation contrasts found in some Central Zapotec languages are a recent development. Cases of tonal contrasts developing out of phonation contrasts are known from Southeast Asia, but Zapotec phonation contrasts arose out of interaction between the glottal consonant and pre-existing tonal contrasts. An exploration of the morphological environments conducive to upstep leads to new discoveries about Zapotecan derivational voice prefixes and reveals the origins of perfective allomorphy.