Phonological history of English open back vowels

In a few varieties of English, the vowel in lot is unrounded, pronounced toward [ɑ]. This is found in the following dialects:

• Most of Irish English
• Much of the Caribbean
• Norwich
• The West Country and the West Midlands of England
• Most of North American English
  • Excluding New England English, where it is typically raised toward /ɔ/, merging with the vowel in thought.

There's also evidence for it in South East England as early as the late 16th century and as late as the 19th century.[2][3]

Linguists disagree as to whether the unrounding of the lot vowel occurred independently in North America (probably occurring around the end of the 17th century) or was imported from certain types of speech current in Britain at that time.

In such accents outside of North America, lot typically is pronounced as [lɑt],[4] therefore being kept distinct from the vowel in palm, pronounced [pɑːm] or [paːm]. However, the major exception to this is North American English, where the vowel is lengthened to merge with the vowel in palm, as described below. This merger is called the LOT–PALM merger or more commonly the father–bother merger. (See further below.)

The LOT–CLOTH split is the result of a late 17th-century sound change that lengthened /ɒ/ to [ɒː] before voiceless fricatives, and also before /n/ in the words gone and sometimes on. It was ultimately raised and merged with /ɔː/ of words like thought, although in some accents that vowel is actually open [ɒː]. This means that CLOTH is not a separate vowel; rather, it means "either LOT or THOUGHT, depending on the accent". The sound change is most consistent in the last syllable of a word, and much less so elsewhere (see below). Some words that entered the language later, especially when used more in writing than speech, are exempt from the lengthening, e.g. joss and Goth with the short vowel. Similar changes took place in words with ⟨a⟩; see trap–bath split and /æ/-tensing.

The cot–caught merger, discussed below, has removed the distinction in some dialects.

As a result of the lengthening and raising, in the above-mentioned accents cross rhymes with sauce, and soft and cloth also have the vowel /ɔː/. Accents affected by this change include American English accents that lack the cot-caught merger and, originally, RP, although today words of this group almost always have short /ɒ/ in RP. The split still exists in some older RP speakers.

The lengthening and raising generally happened before the fricatives /f/, /θ/ and /s/. In American English the raising was extended to the environment before velars /ŋ/ and /ɡ/, and sometimes before /k/ as well, giving pronunciations like /lɔŋ/ for long, /dɔɡ/ for dog and /ˈtʃɔklət/ for chocolate.

In the varieties of American English that have the lot–cloth split, the lot vowel is usually symbolized as /ɑ/, often called the "short o" for historical reasons, as the corresponding RP vowel /ɒ/ is still short (and it contrasts with /ɑː/ as in father and start). The thought vowel is usually transcribed as /ɔ/ and it is often called the "open o". Its actual phonetic realization may be open [ɒ], whereas the lot vowel may be realized as central [ä]. Some words vary as to which vowel they have. For example, words that end in -og like frog, hog, fog, log, bog etc. have /ɑ/ rather than /ɔ/ in some accents.

There are also significant complexities in the pronunciation of written o occurring before one of the triggering phonemes /f θ s ŋ ɡ/ in a non-final syllable. However, the use of the open o as opposed to the short o is largely predictable. Just like with /æ/-tensing and the trap–bath split, there seems to be an open-syllable constraint. Namely, the change did not affect words with /ɑ/ in open syllables unless they were closely derived from words with /ɑ/ in close syllables. Hence /ɔ/ occurs in crossing, crosser, crosses because it occurs in cross; likewise in longing, longer, longest because it occurs in long. However, possible, jostle, impostor, profit, Gothic, bongo, Congo, and boggle all have /ɑ/. However, there are still exceptions in words like Boston and foster.[11][12][13][14][15][16][17][18][19] A further list of words is mentioned in the table below:

Some words may vary depending on the speaker like (coffee, offer, donkey, soggy, boondoggle, etc. with either /ɑ/ or /ɔ/). Meanwhile, other words vary by region. For example, the word on, which in Northern American English dialects without the cot-caught merger is pronounced /ɑn/, rhyming with don, but in Midland and Southern American English without the merger is pronounced /ɔn/, rhyming with dawn. The isogloss for this difference, termed the ON line, lies between New York City and Philadelphia on the East Coast and runs West as far as speakers without the merger can be found.[20]

The cot–caught merger (also known as the low back merger or the LOT–THOUGHT merger) is a phonemic merger occurring in many accents of English, where the vowel sound in words like cot, nod, and stock (the LOT vowel), has merged with that of caught, gnawed, and stalk (the THOUGHT vowel). For example, with the merger, cot and caught become perfect homophones.

The distribution of the vowel transcribed with ⟨ɑː⟩ in broad IPA varies greatly among dialects. It corresponds to /æ/, /ɒ/, /ɔː/ and (when not prevocalic within the same word) /ɑːr/ and even /ɔːr/ in other dialects:

• In non-rhotic dialects spoken outside of North America, /ɑː/ corresponds mostly to /ɑːr/ in General American and so is most often spelled ⟨ar⟩. In dialects with the trap–bath split (such as Received Pronunciation, New Zealand English and South African English), it also corresponds to GA /æ/, which means that it can also be spelled ⟨a⟩ before voiceless fricatives. In those dialects, /ɒ/ and /ɔː/ are separate phonemes.
• In native words, /ɑː/ in most non-rhotic speech of North America corresponds to both /ɑːr/ in GA (RP /ɑː/) and /ɒ/ in RP, as those dialects feature the father–bother merger.
• North American English features the father–bother merger, where /ɑː/ often corresponds to /ɒ/ in RP. Only New York City English and New England English distinguish between the two, and with an unrounded LOT vowel. Modern-day New York City English also has rounded /ɒː/ for reflexes of PALM, which ironically, came from an unrounded vowel.
• The is the cot–caught merger usually occurs in addition to the father-bother merger. This applies to almost all of Canadian English and many varieties of American English. The result is usually /ɑ(ː)/, the PALM vowel, which is used for LOT as well. Some dialects will have /ɒ(ː)/ as the merged vowel, not /ɑ(ː)/; these include Standard Canadian English or Pittsburgh English.
  • The caught-cot merger without the father-bother merger is found in Scottish English and most of New England English. Uniquely, Scottish English merges the LOT vowel into the THOUGHT vowel, rather than the other way around.
• In loanwords and names, the open central unrounded vowel [ä] in a source language is regularly approximated with /ɑ(ː)/ in North America and /æ/ in RP. However, in the case of mid back rounded vowels spelled ⟨o⟩, the usual North American approximation is /oʊ/, not /ɑː/ (in RP, it can be either /əʊ/ or /ɒ/). However, when the vowel is both stressed and word-final, the only possibilities in RP are /ɑː/ in the first case and /əʊ/ in the latter case, mirroring GA.

For the sake of simplicity, instances of an unrounded LOT vowel (phonetically [ɑ]) that do not merge with PALM/START are excluded from the table below. For this reason, the traditional Norfolk dialect is included but the contemporary one, nor the Cardiff dialect, are not.

In many dialects of English, the vowel /oʊ/ has undergone fronting. The exact phonetic value varies. Dialects with the fronted /oʊ/ include Received Pronunciation; Southern, Midland, and Mid-Atlantic American English; and Australian English. This fronting does not generally occur before /l/, a relatively retracted consonant.

• Phonological history of the English language
• Phonological history of English vowels

• Barber, Charles Laurence (1997). Early modern English (second ed.). Edinburgh: Edinburgh University Press. ISBN 0-7486-0835-4.
• Labov, William; Ash, Sharon; Boberg, Charles (2006). The Atlas of North American English: Phonetics, Phonology, and Sound Change: a Multimedia Reference Tool. Berlin; New York: Walter de Gruyter. ISBN 3-11-016746-8.
• Ostalski, Przemysław (2009). "Back Vowels in British and American English" (PDF). Przedsiębiorczość I Zarządzanie. 5 (4): 105–118. Retrieved 2 February 2016.
• Wells, John C. (1982). Accents of English. Vol. 1: An Introduction (pp. i–xx, 1–278), Vol. 2: The British Isles (pp. i–xx, 279–466), Vol. 3: Beyond the British Isles (pp. i–xx, 467–674). Cambridge University Press. ISBN 0-52129719-2, 0-52128540-2, 0-52128541-0.