Phonetics as a complement to phonology in the Canadian Shift.

Previous accounts of the Canadian Shift have interpreted this diachronic change in vowel pronunciation as a purely phonetic consequence of the low back LOT-THOUGHT vowel merger; however, such an analysis does not transparently explain the strong connection between the (phonological) low back merger and the subsequent (phonetic) retraction of the TRAP vowel in the acoustic vowel space. This paper addresses this issue by presenting an analysis of the shift that combines the approaches of Modified Contrastive Specification theory and the Contrastive Hierarchy-two phonological frameworks-with phonetic insights from Vowel Dispersion-Focalization theory. We propose that the catalyst of the Canadian Shift is a three-way vowel merger, in combination with a simultaneous change in the underlying feature specifications of the TRAP vowel. This results in a phonology that allows for the TRAP and DRESS vowels to succumb to the influence of the phonetic principles of dispersion and focalization. This hypothesis is illustrated by comparison of data from 59 speakers in Thunder Bay, Ontario, and Industrial Cape Breton, Nova Scotia. Our analysis predicts that a Canadian Shift-type phonetic change will occur in any North American dialect of English where the PALM-LOT-THOUGHT merger occurs, unless an intervening phonological change alters systemic contrasts.