In keeping with the work in this volume (Becker 2019), we investigate the relationship between the Low Back Merger and the Low-Back-Merger Shift (LBMS), specifically to determine whether overlap of the low back vowels bot and bought precipitates lowering and backing of the short front vowels bit, bet, and bat or whether the two phenomena are coincidental. 1 We draw upon elicited and conversational interview data from contemporary young Californians, one of the North American varieties of English closely identified as a locus of the coincidence of the merger and the shift.

While we can demonstrate a principled link between the Low Back Merger and the LBMS, we also suggest that a more nuanced understanding of the two phenomena is warranted. Notably, we find speakers who are variable in the extent of their low back vowel overlap, yet still participate in the LBMS, suggesting that completion of the merger is not a prerequisite for the initiation of the shift. In short, we align with the account presented in this volume that the Low Back Merger is the initiator of the LBMS and that the movement of bot—not full merger—is enough to trigger shift. In addition, we show that the positions of the low vowels bat, bot, and bought are more variant than bet and bit. Finally, we consider the structural and historical reasons behind the prevalence of the Low Back Merger and why it is a trigger for the LBMS. We posit that the merger and subsequent bat backing are products of acoustic or perceptual instability. Drawing on crossdialectal comparisons, we speculate that our academic framing of the emergence of merged and unmerged Englishes ought be seen not as a function of divergence from some erstwhile unmerged monolith, but as the product of a typology of varieties across which the low back vowel space was never stable in the first place.