Cot–caught merger

The cot–caught merger, also known as the LOT–THOUGHT merger or low back merger, is a phonological phenomenon 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., are examples of minimal pairs that are lost as a result of this sound change; i.e. each of these pairs of words is pronounced the same. The phonemes involved in the cot–caught merger, the low back vowels, are typically represented in the International Phonetic Alphabet as /ɒ/ and /ɔ/ or, for United States English, as /ɑ/ and /ɔ/. The merger is typical of most Indian, 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 PALM /ɑ/, LOT /ɒ/, and THOUGHT /ɔ/.

However, /ɔ/ before /r/ (as in NORTH) participates in a separate phenomenon in most North American English dialects: the NORTH–FORCE merger. So the vowel of /ɔr/ can be phonemicized as the GOAT vowel /oʊ/; therefore, this particular sequence is sometimes alternatively transcribed as /or/ or /oʊr/.