Low back merger shift

The low-back-merger shift is a chain shift of vowel sounds found in several dialects of North American English, beginning in the last quarter of the 20th century and most significantly involving the low back merger accompanied by the lowering and backing of the front lax vowels.

The back and downward movement of all the front lax vowels was first noted as distinguishing certain California English speakers in 1987, and it was soon known by linguists as the California vowel shift. Then, it came to distinguish some Canadian English speakers in 1995, known in that variety as the Canadian shift; today, it helps define Standard Canadian English. The California and Canadian shifts were initially reported as two separate phenomena, but the same basic pattern was next documented among some younger varieties of Western New England English, Western American English, Pacific Northwest English, and Midland American English, all in speakers born after 1980. Linguists have proposed possible relationships between the low back merger and the similarly structured shifts in these regional dialects, though no unifying hypothesis is dominantly agreed upon yet. Assuming the similar chain shifts found in Canada and various parts of the U.S. have a single common origin, a variety of names have been proposed for this trans-regional chain shift which, besides the low-back-merger shift, include the third dialect shift, elsewhere shift, short front vowel shift, and North American shift.

Aside from the low-back-merger shift characterizing these North American varieties, similar, though not identical, shifts to the short front vowels are also attested in other English dialects globally as of 21st-century research, including modern Received Pronunciation, Indian English, Hiberno-English, South African English, and Australian English (the last two dialects traditionally defined by a chain shift moving in the opposite direction of the low-back-merger shift). These changes outside of North America particularly intrigue linguists as they lack the vowel configuration presumed to initiate this shift: the low back merger.