Phonological history of English low back vowels

The phonology of the low back vowels of the English language has undergone changes both overall and with regional variations, through Old and Middle English to the present. The sounds heard in modern English were significantly influenced by the Great Vowel Shift, as well as more recent developments such as the cot–caught merger.



Old and Middle EnglishEdit

In the Old English vowel system, the vowels in the low back area were unrounded: /ɑ/, /ɑː/. There were also rounded back vowels of mid-height: /o/, /oː/. The corresponding spellings were ⟨a⟩ and ⟨o⟩, with the length distinctions not normally marked; in modern editions of Old English texts, the long vowels are often written ⟨ā⟩, ⟨ō⟩.

As the Old English (OE) system developed into that of Middle English (ME), the OE /ɑ/ merged with the fronted /æ/ to become a more central ME /a/. Meanwhile, OE /ɑː/ was rounded and raised to ME /ɔː/. OE /o/ remained relatively unchanged, becoming a short ME vowel regarded as /o/ or /ɔ/, while OE /oː/ became ME /oː/ (a higher vowel than /ɔː/). Alternative developments were also possible; see English historical vowel correspondences for details.

Later, ME open syllable lengthening caused the short vowel to be normally changed to /ɔː/ in open syllables. Remaining instances of the short vowel also tended to become lower. Hence in Late Middle English (around 1400) the following low back vowels were present, distinguished by length:[1]

  • /ɔ/, spelt ⟨o⟩, as in dog, god
  • /ɔː/, often spelt ⟨oa⟩, or ⟨o⟩ before consonant+vowel or certain consonant pairs, as in boat, whole, old

16th-century changesEdit

By 1600, the following changes had occurred:

  • The long vowel /ɔː/ of boat had been raised to /oː/ as a result of the Great Vowel Shift. Before nonprevocalic /r/, the raising did not take place so more was still /mɔːr/.
  • The diphthong /aʊ/ found in words such as cause, law, all, salt, psalm, half, change, chamber, dance had become an open back monophthong /ɔː/
  • At this time, the short /ɔ/ in dog was lowered to /ɒ/

There were, thus, two low back monophthongs:

  • /ɒ/ as in lot
  • /ɔː/ as in cause and (before /r/) in more

and one low back diphthong:

  • /ɔʊ/ as in low

17th-century changesEdit

By 1700, the following further developments had taken place:

  • The diphthong /ɔʊ/ of soul was raised to /oʊ/, and then monophthongized to /o/, merging with boat (see toe–tow merger). The change did not happen before /r/ except in some varieties, as currently seen in Irish English, Scottish English and African American Vernacular English.
  • Short /a/ merged with /ɒ/ when following a /w/, as in want, quality. The merger was suppressed before a velar consonant, as in quack, twang, wag, wax. The change of /wa/ to /wɒ/ did not occur in Mid-Ulster English.
  • /ɒ/ had begun to partake in lengthening and raising before a nonprevocalic voiceless fricative. That resulted in words like broth, cost and off having /ɒː/ instead of /ɒ/, and was the start of the lot–cloth split (see further below).
  • In words such as change and chamber, the pronunciation /ɔː/ was gradually replaced in the standard language by a variant with /eː/, derived from Middle English /aː/. That explains the contemporary pronunciation of these words with /eɪ/.
  • However, when /ɔː/ was proceed by /f/, as in laugh, and half, /ɔː/ was shifted to /æ/ instead, derived from Middle English /a/.
  • An unrounded back vowel /ɑː/ developed, found in certain classes of words that had previously had /a/, like start, father and palm.

That left the standard form of the language with three low back vowels:

  • /ɒ/ in lot and want.
  • /ɔː/ in more, cause, and corn.
  • /ɒː/ in cloth and cost.
  • /ɑː/ in start, father and palm.

Later changesEdit

From the 18th century on, the following changes have occurred:

  • In dialects with the lot-cloth split, the /ɒː/ was raised to /ɔː/, merging with the vowel in thought.
  • In General American, the lot vowel has become unrounded and merged into /ɑː/ (the father–bother merger).
  • In RP, the lot–cloth split has not taken hold so words in the cloth set are usually now pronounced /ɒ/.

This leaves RP with three back vowels:

  • /ɒ/ in lot, want, cloth, and cost.
  • /ɔː/ in more, cause, and corn.
  • /ɑː/ in start, father, and palm.

and General American with two:

  • /ɑː/ in lot, want, start, father, and palm.
  • /ɔː/ in more, cause, corn, cloth and cost.

Unrounded LOTEdit

In a few varieties of English, the vowel in lot is unrounded, shifting from /ɒ/ to /ɑ/ This is found in the following dialects:

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, lot typically is pronounced as /lɑt/,[2] therefore being kept distinct from the vowel in palm, pronounced /pɑːm/. 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.)

Father–bother mergerEdit

The father–bother merger is unrounded lot taken a step further. On top of being unrounded, the vowel in lot and bother is lengthened, merging with the vowel in palm and father.

Examples of possible homophones resulting from the merger include Khan and con (/kɑːn/), Saab and sob (/sɑːb/), and balm and bomb (/bɑːm/, except for some speakers who reintroduce the historical l into balm).[3]

Exceptions to the merger in North America are accents in northeastern New England, such as the Boston accent (in which lot remains rounded, and merges instead with cloth and thought), and some accents of New York City (in which lot is nevertheless unrounded, and the opposition with the /ɑː/-type vowel is somewhat tenuous).[4][5]

LOT–CLOTH splitEdit

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 word gone. In some accents, the lengthened [ɒː] was raised, merging with the /ɔː/ of words like thought. 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.

The cot–caught merger, discussed below, has removed the distinction in some dialects, and may make the lot-cloth split less noticeable.

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 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, including Queen Elizabeth II.

The lengthening and raising generally happened before the fricatives /f/, /θ/ and /s/. In American English the raising was extended to the environment before /ŋ/ and /ɡ/, and in a few words before /k/ as well, giving pronunciations like /lɔːŋ/ for long, /dɔːɡ/ for dog and /ˈɔːklt/ for chocolate.

In the varieties of American English that have the lot–cloth split, the lot vowel is usually symbolized as /ɑ/ and the cloth vowel as /ɔ/, since the distinction is usually one of vowel quality rather than length. The actual pronunciation of these vowels may vary somewhat from the symbol used to denote them; e.g. /ɔ/ is often pronounced closer to a low back rounded vowel [ɒ], and /ɑ/ is sometimes fronted to a low central vowel [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. Normally, when a word is formed by adding a suffix to an existing word, the vowel quality is maintained. Hence /ɔ/ occurs in crossing, crosser, crosses because it occurs in cross; likewise in longing, longer, longest because it occurs in long. In words not formed this way, however, the phoneme /ɑ/ tends to occur even before a triggering phoneme. For example, possible, jostle, impostor, profit, Gothic, bongo, Congo, and boggle all have /ɑ/.[6][7][8][9][10][11][12]

But there are numerous exceptions (e.g. Boston with /ɔ/), including across apparent rhyming pairs (e.g. roster with /ɑ/ but foster often with /ɔ/), as well as a good deal of variation (coffee, offer, donkey, soggy, boondoggle, etc. with either /ɑ/ or /ɔ/, depending on the speaker).[13]

In the Mid-Atlantic U.S. dialect, most famously spoken in metropolitan Philadelphia and Baltimore, the single word on has the same vowel as dawn (in the mid-Atlantic, this is [ɔə~oə]), but not the same vowel as don etc. ([ɑ~ä]). Labov et al. regard this phenomenon as occurring not just in the Mid-Atlantic region, but in all regions south of a geographic boundary that they identify as the ON line, which is significant because it distinguishes most varieties of Northern American English (in which "on" and "Don" are closer rhymes) from most varieties of Midland and Southern American English (in which "on" and "dawn" are closer rhymes).[14]

Cot–caught mergerEdit

Main article: cot–caught merger

The cotcaught merger (also known as the low back merger or the LOT–THOUGHT merger) is a phonemic merger occurring in many English accents, 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.

In the British Isles, this occurs in:

In North American English, the merger is found in:

According to Labov, Ash, and Boberg,[5] the merger does not generally occur in the southern United States (with exceptions), along most of the American side of the Great Lakes region, or in the "Northeast Corridor" extended metropolitan region from Providence, Rhode Island to Baltimore. 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 is in a state of transition.

The merger is also reported in some Singaporean English.[20]

THOUGHT splitEdit

In some London accents of English, the vowel in words such as thought, force, and north, which merged earlier on in these varieties of English, undergoes a conditional split based on syllable structure: closed syllables have a higher vowel quality such as [oː] (possibly even [oʊ] in broad Cockney varieties), and open syllables have a lower vowel quality [ɔ̝ː] or a centering diphthong [ɔə].

Originally-open syllables with an inflectional suffix (such as bored) retain the lower vowel quality, creating minimal pairs such as bored [bɔəd] vs. board [boːd].[21]


The THOUGHT–GOAT merger is a merger of the English vowels /ɔː/ and /oʊ/ that occurs in many female speakers of Geordie.[22] It has also been reported as a possibility in some Northern Welsh accents.[23]


Stages leading to some of the low back vowels of General American, summarized from Wells (1982), with the cotcaught merger added
Middle English ɔ ɔ a
Quality change ɒ ɒ
Thought-monophthonging ɔː
Pre-fricative lengthening ɒː
Quality change ɑː
Lot-unrounding ɑ
Loss of distinctive length ɔ ɒ (ɑ) ɑ
Cloththought merger (ɔ) ɔ
General American Output ɔ ɔ ɑ ɑ
Cotcaught merger ɑ ɑ ɑ ɑ

See alsoEdit


  1. ^ Barber, pp. 108,111
  2. ^ a b c Wells, John C. (1982). Accents of English. Cambridge: Cambridge University Press. ISBN 0-521-22919-7. (vol. 1). ISBN 0-521-24224-X (vol. 2)., ISBN 0-521-24225-8 (vol. 3). , pp. 245, 339–40, 419.
  3. ^ Labov et al. (2006), p 169.
  4. ^ Wells (1982), pp. 136–37, 203–6, 234, 245–47, 339–40, 400, 419, 443, 576.
  5. ^ a b Labov et al. (2006), p. 171.
  6. ^
  7. ^
  8. ^
  9. ^
  10. ^
  11. ^
  12. ^
  13. ^ [1][dead link]
  14. ^ Labov p. 189.
  15. ^ a b Heggarty, Paul et al, eds. (2013). "Accents of English from Around the World". University of Edinburgh. 
  16. ^ a b c Labov p. 60-1.
  17. ^ Gagnon, C. L. (1999). Language attitudes in Pittsburgh: 'Pittsburghese' vs. standard English. Master's thesis. Pittsburgh: University of Pittsburgh. 
  18. ^ Dubois, Sylvia and Barbara Horvath (2004). "Cajun Vernacular English: phonology." In Bernd Kortmann and Edgar W. Schneider (Ed). A Handbook of Varieties of English: A Multimedia Reference Tool. New York: Mouton de Gruyter. p. 409-10.
  19. ^ Labov p. 218.
  20. ^ "Singapore English" (PDF). Retrieved 2017-01-11. 
  21. ^ Przemysław Ostalski. Back Vowels in British and American English. Przedsiębiorczość i Zarządzanie, Tom X, Zeszyt 4, Łódź 2009, ss. 105–118. Retrieved 2 February 2016.
  22. ^ Watt & Allen (2003:269)
  23. ^ Wells (1982:387)


External linksEdit