This dissertation addresses a fundamental question about phonology, i.e. how do we account for the appearance of a phonological rule in a community that had previously never posited one? For example, how could we account for someone who posits a phonological difference between /r/ and /l/, i.e. the two are distinct phonemes in their grammar, when no one in their speech community distinguishes between the two sounds phonologically, i.e. [r] and [l] are simply variants of the same phoneme. The general argument in the literature is that phonological change comes about via re-analysis of some phonetic exaggeration (e.g. Hyman 1975; Ohala 1990; Pierrehumbert 2001; Bermudez-Otero 2007), but because phonological change is rarely observed, there is a paucity of empirical evidence using production data in a community while a change is underway to support this theory. Recent acoustic analyses of large databases of naturally occurring, ongoing phonological changes show that the role of phonetic variation is minor and in some cases non-existent when a phonological rule is innovated (Fruehwald 2013; 2016; Berkson, Davis & Strickler 2017). Therefore, the available empirical evidence for phonological change stands in contrast to what has been proposed in the theoretical literature.This dissertation intervenes in the debate through the analysis of a database of naturally occurring speech in Lansing, Michigan where allophonic change is currently underway. In Lansing, /ae/ is being re-organized such that at the turn of the 20th century, speakers in the community did not distinguish between /ae/ in any phonological environments, speakers born in the 1990s, however, do distinguish between pre-nasal and pre-oral /ae/. I utilize a combination of analyses in this dissertation to account for the initiation and spread of this change throughout the community. First, I conducted an acoustic analysis of /ae/ in F1/F2 space in a corpus of naturally occurring speech by 36 Lansing natives. In particular, I tracked changes in vowel height (F1 at nucleus), backness (F2 at nucleus), diphthongal quality (difference in F1 and F2 at nucleus and offset), and relative distributions of pre-nasal and pre-oral /ae/ token clouds for each speaker (Pillai-Bartlett statistic - see Hay, Warren & Drager 2006; Hall-Lew 2010). I supplemented the acoustic analysis with a sub-phonemic judgement task administered to 107 Lansing natives via an online survey. During the task, respondents were asked to identify whether the vowels in words like pat and pan are the same.This dissertation finds that phonological change was gradual in Lansing. The measure of speaker-level distributions with an impressionistic investigation of divergent trajectories, and the results of the sub-phonemic judgement task suggest that there is indeed an intermediate period between no distinction and phonological difference in Lansing whereby the difference between pre-nasal and pre-oral /ae/ was only phonetically implemented. An analysis of the effects of gender and social class on these measures finds that phonetic variation is socially conditioned in Lansing, such that white-collar women are leading the change away from the community norm. I observe that phonetic exaggeration was promoted by social re-organization in the community, which eventually lead to the development and spread of an allophonic rule. In line with the prediction of Baker, Archangeli, and Mielke (2011), I find that the chance alignment of social and phonetic variability in 20th century Lansing accounts for the initiation and spread of this phonological change.
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