The diachronic trajectories of vowel harmony systems have been understudied but offer significant insight into both the possible domains of vowel harmony as well as the interaction between phonetic coarticulation and phonological harmony. This paper proposes a novel analysis of decaying labial harmony in Kazakh, unifying phonetics and phonology in one formalism (Flemming 2001) that incorporates both abstract morpho-phonological and temporal phonetic factors to drive the gradient harmony pattern in contemporary Kazakh. These factors are defined and implemented in a regression-like model that accurately predicts the degree of coarticulation on non-initial vowels. The structure of the model is then discussed in diachronic terms, outlining the ...