Phonology 33 (2016) 125–167. f Cambridge University Press 2016. doi:10.1017/S0952675716000051 Relating application frequency to morphological structure: the case of Tommo So vowel harmony* Laura McPherson Dartmouth College Bruce Hayes University of California, Los Angeles We describe three vowel-harmony processes in Tommo So and their interaction with morphological structure. The verbal suffixes of Tommo So occur in a strict linear order, establishing a Kiparskian hierarchy of distance from the root. This distance is respected by all three harmony processes; they ‘peter out’, applying with lower fre- quency as distance from the root increases. The function relating application rate to distance is well fitted by families of sigmoid curves, declining in frequency from one to zero. We show that, assuming appropriate constraints, such functions are a direct consequence of Harmonic Grammar. The crucially conflicting constraints are IDENT (violated just once by harmonised candidates) and a scalar version of AGREE (violated one to seven times, based on closeness of the target to the root). We show that our model achieves a close fit to the data, while a variety of alternative models fail to do so. 1 Introduction In Tommo So, a Dogon language of Mali, there are three vowel-harmony processes, all optional. Our focus is on the fact that, for all three processes, * E-mail:
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[email protected]. We would like to thank Robert Daland, Abbie Hantgan, Jeffrey Heath, Kie Zuraw, audiences at the Linguistic Society of America, the Manchester Phonology Meeting, Academia Sinica, Dartmouth College and UCLA, and the an- onymous reviewers and editors for Phonology for their help with this article; all remaining defects are the authors’ responsibility.