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English diphthongs have undergone many changes since the Old and Middle English periods. The sound changes discussed here involved at least one phoneme which historically was a diphthong.

Old English

Further information: Old English phonology and Phonological history of Old English

Old English diphthongs could be short or long. Both kinds arose from sound changes occurring in Old English itself, although the long forms sometimes also developed from Proto-Germanic diphthongs. They were mostly of the height-harmonic type (both elements at the same height) with the second element further back than the first. The set of diphthongs that occurred depended on dialect (and their exact pronunciation is in any case uncertain). Typical diphthongs are considered to have been as follows:

As with monophthongs, the length of the diphthongs was not indicated in spelling, but in modern editions of OE texts the long forms are often written with a macron: ⟨īo⟩, ⟨īe⟩, ⟨ēo⟩, ⟨ēa⟩.

In the transition from Old to Middle English, all of these diphthongs generally merged with monophthongs.

Middle English

Further information: Middle English phonology

Development of new diphthongs

Although the Old English diphthongs merged into monophthongs, Middle English began to develop a new set of diphthongs. Many of these came about through vocalization of the palatal approximant /j/ (usually from an earlier /ʝ/) or the labio-velar approximant /w/ (sometimes from an earlier voiced velar fricative [ɣ]), when they followed a vowel. For example:

Diphthongs also arose as a result of vowel breaking before /h/ (which had allophones [x] and [ç] in this position – for the subsequent disappearance of these sounds, see h-loss). For example:

The diphthongs that developed by these processes also came to be used in many loanwords, particularly those from Old French. For a table showing the development of the Middle English diphthongs, see Middle English phonology (diphthong equivalents).

Vein–vain merger

Early Middle English had two separate diphthongs /ɛj/ and /aj/. The vowel /ɛj/ was typically represented orthographically with "ei" or "ey", and the vowel /aj/ was typically represented orthographically with "ai" or ay". These came to be merged, perhaps by the fourteenth century.[1] The merger is reflected in all dialects of present-day English.

In early Middle English, before the merger, way and day, which came from Old English weġ and dæġ had /ej/ and /aj/ respectively. Similarly, vein and vain (borrowings from French) were pronounced differently as /vejn/ and /vajn/. After the merger, vein and vain were homophones, and way and day rhymed.

The merged vowel was a diphthong, something like /ɛj/ or /æj/. Later (around the 1800s) this diphthong would merge in most dialects with the monophthong of words like pane in the pane–pain merger.

Late Middle English

The English of southeastern England around 1400 had seven diphthongs,[2] of which three ended in /j/:

and four ended in /w/:

Typical spellings are as in the examples above. The spellings eu and ew are both /ɪw/ and /ɛw/, and the spellings oi and oy are used for both /ɔj/ and /ʊj/. The most common words with ew pronounced /ɛw/ were dew, few, hew, lewd, mew, newt, pewter, sew, shew (show), shrew, shrewd and strew. Words in which /ʊj/ was commonly used included boil, coin, destroy, join, moist, point, poison, soil, spoil, Troy, turmoil and voice, although there was significant variation.[2]

Modern English

16th century

By the mid-16th century, the Great Vowel Shift had created two new diphthongs out of the former long close monophthongs /iː/ and /uː/ of Middle English. The diphthongs were /əɪ/ as in tide, and /əʊ/ as in house.[3] Thus, the English of south-eastern England could then have had nine diphthongs.

By the late 16th century, the inventory of diphthongs had been reduced as a result of several developments, all of which took place in the mid-to-late 16th century:[4]

That left /ɪu/, /ɔɪ/, /ʊɪ/, /əɪ/ and /əʊ/ as the diphthongs of south-eastern England.

17th century

By the late 17th century, these further developments had taken place in the dialect of south-eastern England:[4]

The changes above caused only the diphthongs /aɪ/, /aʊ/ and /ɔɪ/ to remain.

Later developments

In the 18th century or later, the monophthongs /eː/ and /oː/ (the products of the panepain and toetow mergers) became diphthongal in Standard English. That produced the vowels /eɪ/ and /oʊ/. In RP, the starting point of the latter diphthong has now become more centralized and is commonly written /əʊ/.

RP has also developed centering diphthongs /ɪə/, /eə/, /ʊə/, as a result of breaking before /r/ and the loss of /r/ when it is not followed by another vowel (see English-language vowel changes before historic /r/). They occur in words like near, square and cure.

Present-day RP is thus normally analyzed as having eight diphthongs: the five closing diphthongs /eɪ/, /əʊ/, /aɪ/, /aʊ/, /ɔɪ/ (of face, goat, price, mouth and choice) and the three centering diphthongs /ɪə/, /eə/, /ʊə/. General American does not have the centering diphthongs (at least, not as independent phonemes). For more information, see English phonology (vowels).

Variation in present-day English

Coilcurl merger

Main article: Rhoticity in English § Coil–curl merger

The coilcurl or oilearl merger is a vowel merger that historically occurred in some non-rhotic dialects of American English, making both /ə/ and /ɔɪ/ become /əɪ/. This is strongly associated with New York City English and New Orleans English, but only the latter has any modern presence of the feature.

Cotcoat merger

The cotcoat merger is a phenomenon exhibited by some speakers of Zulu English in which the phonemes /ɒ/ and /oʊ/ are not distinguished, making "cot" and "coat" homophones. Zulu English often also has a cot-caught merger, so that sets like "cot", "caught" and "coat" can be homophones.[7]

This merger can also be found in some broad Central Belt Scottish English accents. The merger of both sounds into /o/ is standard in Central Scots.

Lineloin merger

The lineloin merger is a merger between the diphthongs /aɪ/ and /ɔɪ/ that occurs in some accents of Southern English English, Hiberno-English, Newfoundland English, and Caribbean English. Pairs like line and loin, bile and boil, imply and employ are homophones in merging accents.[8]

Homophonous pairs
/aɪ/ /ɔɪ/ IPA
aisle oil ˈɑɪl
ally alloy ˈælɑɪ
bile boil ˈbɑɪl
buy boy ˈbɑɪ
by boy ˈbɑɪ
bye boy ˈbɑɪ
buy buoy ˈbɑɪ
by buoy ˈbɑɪ
bye buoy ˈbɑɪ
divide devoid dɪˈvɑɪd
dried droid ˈdrɑɪd
file foil ˈfɑɪl
fire foyer ˈfɑɪə(r)[Note 1]
grind groined ˈɡrɑɪnd
guy goy ˈɡɑɪ
heist hoist ˈhɑɪst
hi hoy ˈhɑɪ
high hoy ˈhɑɪ
I oi ˈɑɪ
I oy ˈɑɪ
I'll oil ˈɑɪl
imply employ ɪmˈplɑɪ
isle oil ˈɑɪl
Jain join ˈdʒɑɪn
Kai coy ˈkɑɪ
Kai koi ˈkɑɪ
kine coin ˈkɑɪn
Kyle coil ˈkɑɪl
liar lawyer ˈlɑɪə(r)
lied Lloyd ˈlɑɪd
line loin ˈlɑɪn
Lyle loyal ˈlɑɪəl[Note 2]
lyre lawyer ˈlɑɪə(r)
mile moil ˈmɑɪl
nighs noise ˈnɑɪz
Nile noil ˈnɑɪl
pie poi ˈpɑɪ
pies poise ˈpɑɪz
pint point ˈpɑɪnt
ply ploy ˈplɑɪ
psi soy ˈsɑɪ
quite quoit ˈkwɑɪt
ride roid ˈrɑɪd
rile roil ˈrɑɪl
rile royal ˈrɑɪəl[Note 2]
rye Roy ˈrɑɪ
sigh soy ˈsɑɪ
sire sawyer ˈsɑɪə(r)
sire soya ˈsɑɪə[Note 3]
Thai toy ˈtɑɪ
tide toyed ˈtɑɪd
tie toy ˈtɑɪ
tile toil ˈtɑɪl
try Troy ˈtrɑɪ
vice voice ˈvɑɪs
vied void ˈvɑɪd
wry Roy ˈrɑɪ

Long mid mergers

The earliest stage of Early Modern English had a contrast between the long mid monophthongs /eː, oː/ (as in pane and toe respectively) and the diphthongs /ɛj, ɔw/ (as in pain and tow respectively). In the vast majority of Modern English accents these have been merged, so that the pairs panepain and toetow are homophones. These mergers are grouped together by Wells[9] as the long mid mergers. All accents with the pane–pain merger have the toe–tow merger and vice versa.

The usual outcome of the merger is /ej/ and /ow/, with some dialects having /eː/ and /oː/. However, a few regional dialects maintain the distinction: East Anglia, south Wales, and in older Northern England, Scottish, Newfoundland, and Maine accents. As late as 1800s England, the distinction was still very widespread; the main areas with the merger were in the northern Home Counties and parts of the Midlands.[10]

In accents that preserve the distinction, the diphthong phoneme /ej/ is usually represented by the spellings ai, ay, ei, and ey as in pain, day, reign, or they; with /ow/ is being the spellings ou, ow, or ol as in soul, tow, bolt, or roll. The monophthong phoneme /eː/ is usually represented by ane, -ange, ae, aCV, ea, and borrowed é and e as in pane, baking, range, Mae, wear, café, and Santa Fe; while /oː/ is usually represented by oa, oe, or oCV as in boat, toe, home, or over.

The distinction is most often preserved in East Anglian accents, especially in Norfolk. Peter Trudgill[11] discusses this distinction, and states that "until very recently, all Norfolk English speakers consistently and automatically maintained the nose-knows distinction ... In the 1940s and 1950s, it was therefore a totally unremarkable feature of Norfolk English shared by all speakers, and therefore of no salience whatsoever." In a recent investigation into the English of the Fens,[12] young people in west Norfolk were found to be maintaining the toe–tow distinction, with back [ʊw] or [ɤʊ] in the toe set and central [ɐʉ] in the tow set. This has tow but not toe showing the influence of Estuary English. However, Trudgill also describes a disappearance of the pane–pain distinction in Norfolk: "This disappearance was being effected by the gradual and variable transfer of lexical items from the set of /eː/ to the set of /æɪ/ as part of dedialectalisation process, the end-point of which will soon be (a few speakers even today maintain a vestigial and variable distinction) the complete merger of the two lexical sets under /æɪ/ – the completion of a slow process of lexical diffusion."[11]

Walters (2001)[13] reports the survival of the distinction in the Welsh English spoken in the Rhondda Valley, with [eː] in the pane words and [ɛj] in the pain words. Likewise, the Rhondda Valley, has [oː] in the toe words and [ow] in the tow words.

Pane–pain pairs
/eː/ /ej/ IPA
ade aid ˈeɪd
ale ail ˈeɪl
ate eight ˈeɪt[Note 4]
bale bail ˈbeɪl
bade bayed ˈbeɪd
blare Blair ˈbleə(r)
blaze Blaise ˈbleɪz
cane Cain ˈkeɪn
clade clayed ˈkleɪd
Clare Claire ˈkleə(r)
bate bait ˈbeɪt
Daly daily ˈdeɪli
Dane deign ˈdeɪn[Note 4]
daze days ˈdeɪz
e'er air ˈeə(r)
e'er heir ˈeə(r)
ere air ˈeə(r)
ere heir ˈeə(r)
fane fain ˈfeɪn
fare fair ˈfeə(r)
faze fays ˈfeɪz
flare flair ˈfleə(r)
gale Gail ˈɡeɪl
gate gait ˈɡeɪt
gaze gays ˈɡeɪz
glave glaive ˈɡleɪv[Note 5]
grade grayed ˈɡreɪd
graze grays ˈɡreɪz
hale hail ˈheɪl
hare hair ˈheə(r)
haze hays ˈheɪz
haze heys ˈheɪz
lade laid ˈleɪd
lane lain ˈleɪn
laze lays ˈleɪz
made maid ˈmeɪd
Mae May ˈmeɪ
male mail ˈmeɪl
mane main ˈmeɪn
maze maize ˈmeɪz
maze Mays ˈmeɪz
page Paige ˈpeɪdʒ
pale pail ˈpeɪl
pane pain ˈpeɪn
pare pair ˈpeə(r)
pear pair ˈpeə(r)
phase fays ˈfeɪz
phrase frays ˈfreɪz
plane plain ˈpleɪn
plate plait ˈpleɪt
Rae ray ˈreɪ
raze raise ˈreɪz
raze rays ˈreɪz
razor raiser ˈreɪzə(r)
re ray ˈreɪ
sale sail ˈseɪl
sane sain ˈseɪn
sane seine ˈseɪn
sane Seine ˈseɪn
spade spayed ˈspeɪd
stare stair ˈsteə(r)
suede swayed ˈsweɪd
tale tail ˈteɪl
there their ˈðeə(r)
there they're ˈðeə(r)
trade trayed ˈtreɪd
vale vail ˈveɪl
vale veil ˈveɪl
vane vain ˈveɪn
vane vein ˈveɪn
wade weighed ˈweɪd[Note 4]
wale wail ˈweɪl
wales wails ˈweɪlz
Wales wails ˈweɪlz
wane wain ˈweɪn
wane Wayne ˈweɪn
waste waist ˈweɪst
wave waive ˈweɪv
waver waiver ˈweɪv
whale wail ˈweɪl[Note 6]
Toe–tow pairs
/oː/ /ou/ IPA
Bo bow ˈboʊ
bode bowed ˈboʊd
borne bourn(e) ˈboə(r)n
borne Bourne ˈboə(r)n
coaled cold ˈkoʊld
coarse course ˈkoə(r)s
do (note) dough ˈdoʊ
doe dough ˈdoʊ
doze doughs ˈdoʊz
floe flow ˈfloʊ
foaled fold ˈfoʊld
fore four ˈfoə(r)
forth fourth ˈfoə(r)θ
fro frow ˈfroʊ
froe frow ˈfroʊ
froze frows ˈfroʊz
groan grown ˈɡroʊn
holed hold ˈhoʊld
moan mown ˈmoʊn
mode mowed ˈmoʊd
Moe mow ˈmoʊ
no know ˈnoʊ
nose knows ˈnoʊz
O owe ˈoʊ
ode owed ˈoʊd
oh owe ˈoʊ
pole poll ˈpoʊl
pore pour ˈpoə(r)
road rowed ˈroʊd
rode rowed ˈroʊd
roe row ˈroʊ
role roll ˈroʊl
rose rows ˈroʊz
shone shewn ˈʃoʊn
shone shown ˈʃoʊn
so sew ˈsoʊ
so sow ˈsoʊ
sole soul ˈsoʊl
soled sold ˈsoʊld
soled souled ˈsoʊld
throe throw ˈθroʊ
throne thrown ˈθroʊn
toad towed ˈtoʊd
toe tow ˈtoʊ
toed towed ˈtoʊd
tole toll ˈtoʊl

Maremayor merger

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The maremayor merger occurs in many varieties of British English, in the Philadelphia dialect, and the Baltimore dialect. The process has bisyllabic /eɪ.ə/ pronounced as the centering diphthong /eə/ in many words. Such varieties pronounce mayor as /ˈmeə(r)/, homophonous with mare.

North American English accents with the merger allow it to affect also sequences without /r/ since some words with the /eɪ.ə/ sequence merge with /eə/, which is associated with æ-tensing. Particularly in the case of /eə/ derived from /æ/, such words are frequently hypercorrected with /æ/. The best-known examples are mayonnaise (/ˈmeəneɪz~ˈmæneɪz/), crayon /ˈkreən~ˈkræn/, and Graham (/ˈɡreəm~ˈɡræm/, a homophone of gram).

Homophonous pairs
/eə/ /eɪə/ IPA
bare Bayer ˈbeə(r)[Note 7]
flare flayer ˈfleə(r)
flair flayer ˈfleə(r)
gram, gramme Graham ˈɡreəm[Note 8]
lair layer ˈleə(r)
mare mayor ˈmeə(r)
pair payer ˈpeə(r)
pare payer ˈpeə(r)
pear payer ˈpeə(r)
prayer prayer ˈpreə(r)
stare stayer ˈsteə(r)
sware swayer ˈsweə(r)
swear swayer ˈsweə(r)
there they're ˈðeə(r)

Prideproud merger

The prideproud merger is a merger of the diphthongs /aɪ/ and /aʊ/ before voiced consonants into monophthongal /a/ occurring for some speakers of African American Vernacular English; making pride and proud, dine and down, find and found, etc. homophones. Some speakers with this merger may also have the rod–ride merger hence having a three–way merger of /ɑ/, /aɪ/ and /aʊ/ before voiced consonants, making pride, prod, and proud and find, found and fond homophones.[14]

Homophonous pairs
/aɪ/ /aʊ/ IPA Notes
bi bough ˈba
bi bow ˈba
bide bowed ˈbad
bight bout ˈbat
bite bout ˈbat
brine brown ˈbran
buy bough ˈba
buy bow ˈba
by bough ˈba
by bow ˈba
bye bough ˈba
bye bow ˈba
chai chow ˈtʃa
Clyde cloud ˈklad
dine down ˈdan
dire dour ˈda(ə)r
dyne down ˈdan
file foul ˈfal
file fowl ˈfal
find found ˈfand
fined found ˈfand
flight flout ˈflat
Giles jowls ˈdʒalz
hi how ˈha
high how ˈha
hind hound ˈhand
I ow ˈa
I'll owl ˈal
ire hour ˈa(ə)r
ire our ˈa(ə)r
isle owl ˈal
Kai cow ˈka
Kyle cowl ˈkal
liar lour ˈla(ə)r
lice louse ˈlas
lied loud ˈlad
light lout ˈlat
lite lout ˈlat
lyre lour ˈla(ə)r
lyse louse ˈlas
mice mouse ˈmas
mind mound ˈmand
mined mound ˈmand
nigh now ˈna
nine noun ˈnan
Nye now ˈna
phial foul ˈfa(ə)l With vile-vial merger.
phial fowl ˈfa(ə)l With vile-vial merger.
ply plow; plough ˈpla
pride proud ˈprad
pried proud ˈprad
pries prows ˈpraz
prise prows ˈpraz
prize prows ˈpraz
pry prow ˈpra
pyre power ˈpa(ə)r
ride rowed ˈrad
right rout ˈrat
right route ˈrat
rind round ˈrand]
rise rouse ˈraz
rise rows ˈraz
rite rout ˈrat
rite route ˈrat
rye row ˈra
ryes rouse ˈraz
sai sow ˈsa
sigh sow ˈsa
signed sound ˈsand]
sire sour ˈsa(ə)r
size sows ˈsaz
sly slough ˈsla
thy thou ˈða
tie tau ˈta
tight tout ˈtat
tine town ˈtan
trite trout ˈtat
Ty tau ˈta
vie vow ˈva
why wow ˈwa With wine-whine merger.
wise wows ˈwaz
Y; wye wow ˈwa

Rodride merger

The rodride merger is a merger of /ɑ/ and /aɪ/ occurring for some speakers of Southern American English and African American Vernacular English, in which rod and ride are merged as /rad/.[14] Some other speakers may keep the contrast, so that rod is /rɑd/ and ride is /rad/.

Homophonous pairs
/ɑ/ /aɪ/ IPA Notes
ah eye ˈa
ah I ˈa
baa buy ˈba
baa by ˈba
baa bye ˈba
blot blight ˈblat
bock bike ˈbak
bod bide ˈbad
bot bight ˈbat
bot bite ˈbat
box bikes ˈbaks
con kine ˈkan
cot kite ˈkat
doc dike ˈdak
dock dike ˈdak
dom dime ˈdam
Dom dime ˈdam
don dine ˈdan
Don dine ˈdan
fa fie ˈfa
far fire ˈfar
grom grime ˈgram
ha high ˈha
hock hike ˈhak
hot height ˈhat
jar gyre ˈdʒar
job gibe, jibe ˈdʒab
knot knight ˈnat
knot night ˈnat
la lie ˈla
la lye ˈla
lock like ˈlak
lot light, lite ˈlat
lox likes ˈlaks
ma my ˈma
mar mire ˈmar
mock mic ˈmak
mock Mike ˈmak
mom mime ˈmam
motte might ˈmat
motte mite ˈmat
nah nigh ˈna
nah Nye ˈna
not knight ˈnat
not night ˈnat
odd ide ˈad
odds ides ˈadz
ox Ike's ˈaks
pa pi ˈpa
pa pie ˈpa
par pyre ˈpar
pock pike ˈpak
pod pied ˈpad
plod plied ˈplad
plot plight ˈplat
pop pipe ˈpap
pox pikes ˈpaks
prod pride ˈprad
prod pried ˈprad
prom prime ˈpram
rah rye ˈra
roc Reich ˈrak
rock Reich ˈrak
rod ride ˈrad
ROM rime ˈram
ROM rhyme ˈram
rot right ˈrat
rot rite ˈrat
scrod scried ˈskrad
shah shy ˈʃa
shod shied ˈʃad
slot sleight ˈslat
slot slight ˈslat
sock psych ˈsak
sod side ˈsad
sod sighed ˈsad
sot sight ˈsat
spa spy ˈspa
spar spire ˈspar
spot spite ˈspat
strop stripe ˈstrap
swan swine ˈswan
swap swipe ˈswap
ta tie ˈta
tar tire, tyre ˈtar
tod tide ˈtad
tod tied ˈtad
Todd tide ˈtad
Todd tied ˈtad
tom time ˈtam
tom thyme ˈtam
Tom time ˈtam
Tom thyme ˈtam
top type ˈtap
tot tight ˈtat
trod tried ˈtrad
trot trite ˈtrat
wad why'd ˈwad With wine-whine merger.
wad wide ˈwad
watt white ˈwat With wine-whine merger.
watt wight ˈwat

Smoothing of /aɪ.ə/

Smoothing of /aɪ.ə/ is a process that occurs in many varieties of British English where bisyllabic /aɪ.ə/ becomes the triphthong /aɪə/ in certain words with /aɪ.ə/. As a result, "scientific" is pronounced /saɪənˈtɪf.ɪk/ with three syllables and "science" is pronounced /ˈsa(ɪ)əns/ with one syllable.[15]

See also


  1. ^ Foyer may also be pronounced /ˈfɑɪeɪ/ or /ˈfwɑːjeɪ/.
  2. ^ a b With vilevial merger
  3. ^ Non-rhotic accents
  4. ^ a b c With waitweight merger
  5. ^ Homonyms
  6. ^ With winewhine merger
  7. ^ North American English pronunciation of Bayer
  8. ^ With æ-tensing


  1. ^ Wells (1982), p. 192
  2. ^ a b Barber (1997), pp. 112–116
  3. ^ Barber (1997), p. 108
  4. ^ a b Barber (1997), pp. 108, 116
  5. ^ a b Mazarin, André (2020-01-01). "The developmental progression of English vowel systems, 1500–1800: Evidence from grammarians". Ampersand. 7: 100058. doi:10.1016/j.amper.2020.100058. ISSN 2215-0390. S2CID 212820754.
  6. ^ Barber (1997), pp. 115–116
  7. ^ "Rodrik Wade, MA Thesis, Ch 4: Structural characteristics of Zulu English". Archived from the original on May 17, 2008. Retrieved 2008-05-17.
  8. ^ Wells (1982), pp. 208–210
  9. ^ Wells (1982), pp. 192–194, 337, 357, 384–385, 498
  10. ^ Britain (2001)
  11. ^ a b "Norfolk England Dialect Orthography". Friends of Norfolk Dialect. Archived from the original on 2008-02-22. Retrieved 2019-02-13.
  12. ^ Britain (2002)
  13. ^ Walters (2001)
  14. ^ a b Wells (1982), p. 557
  15. ^ Wells, John "Whatever happened to received pronunciation?" Wells: Whatever happened to received pronunciation? Author's webpage; accessed 19 April 2011.