Cot-caught merger

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The areas enclosed by the green line are those where most speakers have completely merged the vowels of cot and caught. The areas enclosed by the blue line are those where most local speakers maintain the distinction to some degree, including transitional areas where the two sounds are similar or speakers are inconsistent. Unenclosed areas are those where all speakers are transitional or for which there are insufficient data to determine their status. Data according to the Telsur Project ( by William Labov et al.

In linguistics, the cot-caught merger (also known as the low back merger) is a phonemic merger, a sound change, that occurs in some varieties of English.

The sound change causes the vowel in words like cot, rock, and doll to be pronounced the same as the vowel in the words caught, talk, law, and small, so that for example cot and caught become homophones, and the two vowel classes become merged as a single phoneme. This sound change appears to have occurred at some time in the nineteenth century. A folk etymology of the expression O.K., which holds that it stands for oll korrect, a joke misspelling of all correct, shows that the merger had begun to take root in North America by the 1830s, when this explanation for the expresion was first attested. The presence of the merger and its absence are both found in many different regions of the continent, and in both urban and rural environments.

The symbols traditionally used to transcribe the vowels in the words "cot" and "caught" as spoken in American English are open back unrounded vowel and open-mid back rounded vowel, respectively, but recent sociolinguistic phonetics research has shown that for many American English speakers, the vowels are actually closer to the cardinal vowels open mid unrounded vowel and open back rounded vowel. The precise phonetic value of the merged vowel varies from region to region, as do the phonetic values of the unmerged vowel in regions where the merger has not occurred.

According to the Telsur Project ( of William Labov and others, the merger does not generally occur in the southern United States, along the American side of the Great Lakes region, or in the "Northeast Corridor" extended metropolitan region from New York City to Baltimore. It occurs in most forms of Canadian English west of Quebec, in the Boston, Massachusetts area and northern New England (see Boston accent), and in the eastern Ohio River valley. West of the line formed by the borders of North Dakota down through Oklahoma and in western Texas, the merger is usual. The distribution of the merger is complex, even without taking into account the mobility of the American population; there are pockets of speakers with the merger in areas that lack it, and vice versa. There are areas where the merger has only partially occurred, or are in a state of transition. The Telsur Project focuses on subjects who were born and raised and whose parents grew up in the city where they lived at the time of the interview. Another dialect survey (, in which subjects did not necessarily live in the same city where they were born and where their parents grew up, indicates that there are speakers of both merging and contrast-preserving accents throughout the country. Both surveys indicate that approximately 60% of American English speakers preserve the contrast, while approximately 40% make the merger.

Three phenomena that have been identified as accompanying resistance to the merger are:

  • The raising of the "caught" vowel past position
  • The presence of the northern cities vowel shift, a chain sound change that affects the pronunciation of several back vowels;
  • The presence of certain features of southern American English, and specifically the use of a back upglide for the "caught" vowel.

For those who have the merger, the two sounds and are allophones; they often do not perceive differences in their usage, hear neither of them as a separate phoneme, and hear the distinct vowels used by speakers whose dialects do distinguish them as variations on the same vowel. They hear the broad A of British Received Pronunciation as the same, single vowel sound. But in Received Pronunciation, there are three sounds distinguished: the long of cart, the long of caught, and the short rounded of cot. For most American speakers that have the merger, the merged caught-cot vowel is usually realized as , but for eastern Canadian speakers and speakers from northeastern New England, it is commonly a more rounded vowel close to .

The Telsur Project results also reveal that about 15% of respondents have the merger before but not before , so that Don and Dawn are homophonous, but cot and caught are not. A much smaller group (about 4%) has the reverse situation: cot and caught are homophonous but Don and Dawn are distinct.

Outside of North America, the merger occurs in some accents of Scottish English (Wells (1982), p400) and to some extent in the English of Northern Ireland (Wells (1982), p443).



  • Wells, J. C. (1982). Accents of English 2: The British Isles. Cambridge: Cambridge University Press. ISBN 0521285402.

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