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History and description of
English pronunciation
Historical stages
Old English Middle English
General development
In Old English In Scots
Development of vowels
A Close back Close front Diphthongs Great Vowel Shift Open back Pre-L Pre-R
Development of consonants
Single consonants Clusters
Variable features
Cot–caught merger Drawl Flapping H-dropping L-vocalization NG R Rhoticity T-glottalization TH WH
Related topics
History of English Spelling

The phonology of the open 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 in some dialects such as the cot–caught merger.

In the Old English vowel system, the vowels in the open 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 short vowel /ɑ/ merged with the fronted /æ/ to become a more central ME /a/. Meanwhile, the OE long vowel /ɑː/ was rounded and raised to ME /ɔː/. OE short /o/ remained relatively unchanged, becoming a short ME vowel regarded as /o/ or /ɔ/, while OE long /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 /o/ to be normally changed to /ɔː/ in open syllables. Remaining instances of the short vowel /o/ also tended to become lower. Hence in Late Middle English (around 1400) the following open 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

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.
• The diphthong /aw/ found in words such as cause, law, all, salt, psalm, half, change, chamber, dance had become an open back monophthong /ɔː/ or /ɑː/.
• At this time, the short /ɔ/ in dog was lowered to /ɒ/

There were thus two open back monophthongs:

• /ɒ/ as in lot
• /ɔː/ or /ɑː/ as in cause

and one open back diphthong:

• /ɔw/ as in low

By 1700, the following further developments had taken place:

• The diphthong /ɔw/ of soul was raised to /ow/, and then monophthongized to /oː/, merging with boat (see toe–tow merger). Before /r/, this vowel further merged with /ɔː/ due to the horse–hoarse merger except in some varieties, as currently seen in Irish English, Scottish English and African American Vernacular English.
• Short /wa/ was retracted and rounded to /wɒ/. The shift was suppressed before a velar consonant, as in quack, twang, wag, wax, and also was suppressed by analogy in swam (the irregular past tense of swim). 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 or /r/. 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/ preceded /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 four open back vowels:

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

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

• The three-way distinction between /ɒ/, /ɒː/, and /ɔː/ was simplified in one of two ways:
  • In General American and old-fashioned RP, /ɒː/ was raised to /ɔː/, merging with the vowel in THOUGHT (the cloth-thought merger).
  • In many accents of England, the lengthening of the CLOTH set was undone, restoring the short pronunciation /ɒ/. This became standard RP by the mid-20th century.
• In General American, the lot vowel has become unrounded and merged into /ɑ/ (the father–bother merger).

This leaves RP with three back vowels:

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

and General American with two:

• /ɑ/ in lot, want, start, father, and palm.
• /ɔ/ in tor, cause, corn, cloth and cost.

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 northeastern New England English and Western Pennsylvania 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^[which?] 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.^{[citation needed]}

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 father–bother merger is a phonemic merger of the lexical sets LOT and PALM. It represents unrounded lot, as detailed above, taken a step further. On top of being unrounded, the length distinction between the vowel in lot and bother and the vowel in palm and father is lost, so that the two groups merge. This causes father and bother to become rhymes.

This occurs in the great majority of North American accents; of the North American dialects that have unrounded lot, the only notable exception to the merger is New York City English, where the opposition with the [ɑ]-type vowel is somewhat tenuous.^[5][6]

Examples of possible homophones resulting from the merger include Khan and con (/kɑn/) as well as Saab and sob (/sɑb/).^[7]

While the accents in northeastern New England, such as the Boston accent, also remain unmerged, lot remains rounded and merges instead with cloth and thought.^[5][6]

Homophonous pairs

/ɑ:/	/ɒ/ or /ɔ/[a]	IPA (using ⟨ɑ⟩ for the merged vowel)	Notes
ah	awe	ˈɑ	with the cot-caught merger
balm	bomb	ˈbɑm	when the <l> in balm is unsounded
Bali	bolly[8]	ˈbɑli
baht	bot	ˈbɑt
baht	bought	ˈbɑt	with the cot-caught merger
Dalí	dolly	ˈdɑli
Hajj	Hodge	ˈhɑdʒ
Khan	con	ˈkɑn
la[9]	law	ˈlɑ	with the cot-caught merger
lager	logger	ˈlɑgər
Mali	Molly	ˈmɑli
pa	paw	ˈpɑ	with the cot-caught merger
palm	pom	ˈpɑm	when the <l> in palm is unsounded
Prague	prog[10]	ˈprɑg
Raab	rob	ˈrɑb
Saab	sob	ˈsɑb
Shah	Shaw	ˈʃɑ	with the cot-caught merger
Siân	Sean, Shaun, Shawn	ˈʃɑn	with the cot-caught merger
Siân	shone	ˈʃɑn
Stalin	stalling	ˈstɑlɪn	with the cot-caught merger and G-dropping.

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 formerly RP, although with the exception of water /wɔːtə(r)/, today words of this group almost always have short /ɒ/ in RP.

The lengthening and raising generally happened before the fricatives /f/, /θ/, and /s/, and in the word water for an unknown reason (compare the broadening of a in father). 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/ in some accents and /ɔ/ in others.

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. In other cases, 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 closed syllables. Hence /ɔ/ occurs in crossing, crosser, crosses because it occurs in cross. In contrast, possible, jostle, impostor, profit, Gothic, and boggle all have /ɑ/. However, there are still exceptions in words like Boston and foster.^{[11][12][13][14][15][16][17]} A further list of words is mentioned in the table below:

Vowels with lot–cloth splits

Set	THOUGHT (/ɔ/)	LOT (/ɑ/)	Variable
/-f/	coffer, coffin, cough, off, office, often, soften, trough, etc.	philosophical, profit	coffee, offense, offer, waffle
/-ft/	croft, loft, lofty, soft, etc.	waft	—
/-g/	dog	boggle, cog, flog	blog, boondoggle, fog, frog, hog, log, soggy, tog, etc.
/-k/	bock, chocolate	all other words in this set	clock, mock, shock
/-n/	gone	all other words in this set	beyond, on, upon, want[b], wont
/-ŋ/	long, longest, song, strong, thong, wrong, etc.	Congo, bongo, congress, conquer	donkey, conch
/-s/	boss, cross, floss, glossy, loss, moss, toss, etc.	apostle, fossil, jostle, oscillate, philosophy, posse, possible, possum, rhinoceros, velocity	glossary
/-st/	accost, Boston, cost, foster, frost, lost	apostrophe, (a/pro)gnostic, hostage, hostel, hostile, impostor, nostril, ossify, ostensible, ostentatious, ostracism, posterity, prosecute, roster	Gloucester, nostalgia, ostrich, rostrum
/-ʃ/	Washington, wash, washer	all other words in this set	gosh, quash, squash, swash
/-tər/	water	all other words in this set	—
/-θ/	broth, cloth, froth, moth, etc.	Goth, Gothic	sloth, swath, troth, wrath

Some words may vary depending on the speaker like (coffee, offer, donkey, soggy, boondoggle, etc. with either /ɑ/ or /ɔ/).^{[citation needed]} 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.^[19] Pronunciation of the word want as /wɔnt/ is also strongly associated with the South.^[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.

Lexical changes in cot–caught merger dialects of North America

Lexical set	Example words	Change	GenAm phonemes	Minimal pairs	IPA	Change	Cot–caught merger dialects
PALM	ah, father, spa	Father–bother merger	/ɑ/	cot, collar, stock, wok, chock, Don	/kɑt/, /ˈkɑlər/, /stɑk/, /wɑk/, /tʃɑk/, /dɑn/	Cot–caught merger	/kɑt/, /ˈkɑlər/, /stɑk/, /wɑk/, /tʃɑk/, /dɑn/
LOT	bother, lot, wasp
CLOTH	boss, cloth, dog, off	Cloth-thought merger	/ɔ/	caught, caller, stalk, walk, chalk, dawn	/kɔt/, /ˈkɔlər/, /stɔk/, /wɔk/, /tʃɔk/, /dɔn/
THOUGHT	all, thought, flaunt

The GOAT–THOUGHT merger is a merger of the English vowels of GOAT /oʊ/ and THOUGHT /ɔː/ that has been reported in Geordie since the late 20th century, with a quality around [oː]. The merger is more common among younger female speakers.^[21]

The merger also exists among older speakers in Bradford English with a quality around [ɔː], but younger speakers are more likely to resist the merger by fronting the GOAT vowel.^[21]

Homophonous pairs

/ɔo:/	/oʊ/	IPA (using ⟨oː⟩ for the merged vowel)	Notes
aboard	abode	əˈboːd	non-rhotic with the horse-hoarse merger
alder	older	ˈoːdə
augur	ogre	ˈoːgə
auk	oak	ˈoːk
awe	O	ˈoː
awe	oh	ˈoː
awe	owe	ˈoː
awed	ode	ˈoːd
awning	owning	ˈoːnɪŋ
bald	bold	ˈboːld
bald	bowled	ˈboːld
ball	bowl	ˈboːl
boar	beau	ˈboː	non-rhotic with the horse-hoarse merger
bore	beau	ˈboː	non-rhotic with the horse-hoarse merger
boar	bow	ˈboː	non-rhotic with the horse-hoarse merger
bore	bow	ˈboː	non-rhotic with the horse-hoarse merger
board	bode	ˈboːd	non-rhotic with the horse-hoarse merger
bored	bode	ˈboːd	non-rhotic with the horse-hoarse merger
born	bone	ˈboːn	non-rhotic
caulk	coke	ˈkoːk
call	coal	ˈkoːl
caller	cola	ˈkoːlə	non-rhotic
caught	coat	ˈkoːt
cawed	code	ˈkoːd
chalk	choke	ˈtʃoːk
chord	code	ˈkod	non-rhotic
clause	close	ˈkloːz
claws	close	ˈkloːz
cord	code	ˈkoːd	non-rhotic
cork	coke	ˈkoːk	non-rhotic
corks	coax	ˈkoːks	non-rhotic
court	coat	ˈkoːt	non-rhotic with the horse-hoarse merger
daunt	don't	ˈdoːnt
door	doe	ˈdoː	non-rhotic with the horse-hoarse merger
drawl	droll	ˈdroːl
drawn	drone	ˈdroːn
explored	explode	ˈɪksploːd	non-rhotic with the horse-hoarse merger
fall	foal	ˈfoːl
fawn	phone	ˈfoːn
flaw	flow	ˈfloː
floor	flow	ˈfloː	non-rhotic with the horse-hoarse merger
for	foe	ˈfoː	non-rhotic
fore	foe	ˈfoː	non-rhotic with the horse-hoarse merger
fork	folk	ˈfoːk	non-rhotic
form	foam	ˈfoːm	non-rhotic
four	foe	ˈfoː	non-rhotic with the horse-hoarse merger
gall	goal	ˈgoːl
galled	gold	ˈgoːld
Gaul	goal	ˈgoːl
gnaw	know	ˈnoː
gnaw	no	ˈnoː
hall	hole	ˈhoːl
hall	whole	ˈhoːl
haul	hole	ˈhoːl
haul	whole	ˈhoːl
hauled	hold	ˈhoːld
haw	ho	ˈhoː
haw	hoe	ˈhoː
hawks	hoax	ˈhoːks
hoard	hoed	ˈhoːd	non-rhotic with the horse-hoarse merger
horn	hone	ˈhoːn	non-rhotic
jaw	Joe	ˈdʒoː
laud	lord	ˈloː
law	low	ˈloː
lawn	loan	ˈloːn
lawn	lone	ˈloːn
lord	load	ˈloːd	non-rhotic
lore	low	ˈloː	non-rhotic with the horse-hoarse merger
mall	mole	ˈmoːl
maul	mole	ˈmoːl
mauled	mould	ˈmoːld
maw	mow	ˈmoː
more	mow	ˈmoː	non-rhotic with the horse-hoarse merger
mortar	motor	ˈmoːtə	non-rhotic
nor	know	ˈnoː	non-rhotic
nor	no	ˈnoː	non-rhotic
norm	gnome	ˈnoːm	non-rhotic
nought	note	ˈnoːt
oar	O	ˈoː	non-rhotic with the horse-hoarse merger
oar	oh	ˈoː	non-rhotic with the horse-hoarse merger
oar	owe	ˈoː	non-rhotic with the horse-hoarse merger
or	O	ˈoː	non-rhotic
or	oh	ˈoː	non-rhotic
or	owe	ˈoː	non-rhotic
order	odour	ˈoːdə	non-rhotic
ore	O	ˈoː	non-rhotic with the horse-hoarse merger
ore	oh	ˈoː	non-rhotic with the horse-hoarse merger
ore	owe	ˈoː	non-rhotic with the horse-hoarse merger
overawed	overrode	oːvəˈroːd
pall	pole	ˈpoːl
Paul	pole	ˈpoːl
pause	pose	ˈpoːz
paws	pose	ˈpoːz
pores	pose	ˈpoːz	non-rhotic with the horse-hoarse merger
pours	pose	ˈpoːz	non-rhotic with the horse-hoarse merger
porch	poach	ˈpoːtʃ	non-rhotic with the horse-hoarse merger
pork	poke	ˈpoːk	non-rhotic with the horse-hoarse merger
portion	potion	ˈpoː	non-rhotic with the horse-hoarse merger
prawn	prone	ˈproːn
quart	quote	ˈkwoːt	non-rhotic
raw	row	ˈroː
roar	row	ˈroː	non-rhotic with the horse-hoarse merger
saw	sew	ˈsoː
saw	so	ˈsoː
scald	scold	ˈskoːld
scrawl	scroll	ˈskroːl
shawl	shoal	ˈʃoːl
Shaun	shown	ˈʃoːn
Shaw	show	ˈʃoː
shore	show	ˈʃoː	non-rhotic with the horse-hoarse merger
shorn	shown	ˈʃoːn	non-rhotic with the horse-hoarse merger
slaw	slow	ˈsloː
snore	snow	ˈsnoː	non-rhotic with the horse-hoarse merger
stalk	stoke	ˈstoːk
stall	stole	ˈstoːl
store	stow	ˈstoː	non-rhotic with the horse-hoarse merger
stork	stoke	ˈstoːk	non-rhotic
strawed	strode	ˈstroːd
talk	toque	ˈtoːk
taught	tote	ˈtoːt
taut	tote	ˈtoːt
tor	toe	ˈtoː	non-rhotic
tor	tow	ˈtoː	non-rhotic
tore	toe	ˈtoː	non-rhotic with the horse-hoarse merger
tore	tow	ˈtoː	non-rhotic with the horse-hoarse merger
torn	tone	ˈtoːn	non-rhotic with the horse-hoarse merger
tawny	Tony	ˈtoːni
trawl	troll	ˈtroːl
walk	woke	ˈwoːk
walled	wold	ˈwoːld
war	woe	ˈwoː	non-rhotic
ward	wode	ˈwoːd	non-rhotic
warred	wode	ˈwoːd	non-rhotic
yore	yo	ˈjoː	non-rhotic with the horse-hoarse merger
York	yolk	ˈjoːk
York	yoke	ˈjoːk

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].^[22]

In broad Geordie, some THOUGHT words (roughly, those spelled with a, as in walk and talk) have [aː] (which phonetically is the long counterpart of TRAP /a/) instead of the standard [ɔː]. Those are the traditional dialect forms which are being replaced with the standard [ɔː]. [aː] is therefore not necessarily a distinct phoneme in the vowel system of Geordie, also because it occurs as an allophone of /a/ before voiced consonants.^[23]

The WRATH-ROTH merger is a merger of the English vowel of WRATH /æ~ɑː/ into the vowel of ROTH /ɒ~ɔ(ː)/ that appears in Received Pronunciation and some speakers of New Zealand English, occurring only when the vowel appears after wr (historical /wr/).

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 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.
• 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.

/ɑː/ in native words and non-recent loanwords

Variety	Rhotic	Mergers and splits									Possible spellings
		/ɒrV-ɑːrV/ merger	card-cord merger	cot-caught merger	father–bother merger	father–farther merger	god-guard merger	lot-cloth split	trap-palm merger	trap-bath split	⟨a⟩	⟨ar⟩	⟨au⟩[c]	⟨aw⟩	⟨o⟩	⟨or⟩
Australian English	no	no	no	no	no	yes	no	no	no	partial[d]	yes	yes	no	no	no	no
Canadian English	yes	no	no	yes	variable	—	—	—	no	no	yes	no	yes	yes	yes	no
General American	yes	no	no	variable	yes	—	—	yes	no	no	yes	no	variable	variable	yes	no
Hiberno-English	yes	no	no	variable	no	—	—	variable	variable	variable	variable	no	no	no	no	no
New York City English	variable	possible	no	no	variable	variable	variable	yes	no	no	yes	no	no	no	variable	no
New Zealand English	mostly no	no	no	no	no	mostly yes	no	no	no	yes	yes	mostly yes	no	no	no	no
Northeastern New England English	variable	no	no	yes	no	variable	no	—	no	no	yes	yes	no	no	no	no
Northern England English	no	no	no	no	no	yes	no	no	no	no	yes	yes	no	no	no	no
Philadelphia English	yes	possible	no	no	yes	—	—	yes	no	no	yes	no	no	no	yes	no
Received Pronunciation	no	no	no	no	no	yes	no	no	no	yes	yes	yes	no	no	no	no
Scottish English	yes	no	no	mostly yes	no	—	—	— (mostly)	mostly yes	mostly no	mostly no	no	no	no	no	no
South African English	mostly no	no	no	no	no	mostly yes	no	variable	no	yes	yes	mostly yes	no	no	no	no
Southern American English	variable	mostly no	mostly no	variable	yes	variable	variable	yes	no	no	yes	variable	variable	variable	yes	mostly no
Traditional Norfolk dialect	no	variable	no	no	variable	yes	variable	yes	no	yes	yes	yes	no	no	yes	no
Welsh English	mostly no	no	no	no	no	mostly yes	no	no	no	variable	yes	yes	no	no	no	no

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.

Stages leading to some of the open back vowels of General American, summarized from Wells (1982), with the cot–caught merger added

	law ball taught caught	off cloth loss	lot stop rob cot bother	father palm calm
Middle English	au̯	ɔ		a
Quality change	au̯	ɒ		a
Thought-monophthonging	ɔː	ɒ		a
Pre-fricative lengthening	ɔː	ɒː	ɒ	a
A-lengthening	ɔː	ɒː	ɒ	aː
Quality change	ɔː	ɒː	ɒ	ɑː
Lot-unrounding	ɔː	ɒː	ɑ	ɑː
Loss of distinctive length	ɔ	ɒ	ɑ	ɑ
Cloth–thought merger	ɔ	ɔ	ɑ	ɑ
General American output	ɔ		ɑ
Cot–caught merger	ɑ

• Phonological history of English
• 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. doi:10.1017/CBO9780511611759, 10.1017/CBO9780511611766. ISBN 0-52129719-2 , 0-52128540-2 , 0-52128541-0 .