Cot–caught merger

The cot–caught merger, also known as the merger or low back merger, is a sound change present in some dialects of English where speakers do not distinguish the vowel phonemes in words like cot versus caught. Cot and caught (along with bot and bought, pond and pawned, etc.) is an example of a minimal pair that is lost as a result of this sound change. The phonemes involved in the cot–caught merger, the low back vowels, are typically represented in the International Phonetic Alphabet as /ɒ/ and /ɔ/, respectively (or, in North America, co-occurring with the father–bother merger, as /ɑ/ and /ɔ/). The merger is typical of most Canadian and Scottish English dialects as well as some Irish and U.S. English dialects. An additional vowel merger, the father–bother merger, which spread through North America in the eighteenth and nineteenth centuries, has resulted today in a three-way merger in which most Canadian and many U.S. accents have no vowel difference in words like /ɑ/, /ɒ/, and /ɔ/. However, /ɔr/ as in participates in a separate phenomenon in most North American English: the merger, in which this vowel before /r/ can be phonemicized as the vowel, transcribed variously thus as /or/ or /oʊr/. The shift causes the vowel sound in words like cot, nod and stock and the vowel sound in words like caught, gnawed and stalk to merge into a single phoneme; therefore the pairs cot and caught, stock and stalk, nod and gnawed become perfect homophones, and shock and talk, for example, become perfect rhymes.