Phonological history of English diphthongs

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[]

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 ions 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[]

Development of new diphthongs[]

Although the Old English diphthongs merged into monophthongs, Middle English began to develop a new set of diphthongs, in which the second element was a high [i] or [u]. Many of these came about through vocalization of the palatal approximant /j/ or the labio-velar approximant /w/ (which was sometimes from an earlier voiced velar fricative [ɣ], an allophone of /ɡ/), 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 /ɛi/ and /ai/. The vowel /ɛi/ was typically represented orthographically with "ei" or "ey" and the vowel /ai/ 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 /ei/ and /ai/ respectively. Similarly, vein and vain (borrowings from French) were pronounced differently as /vein/ and /vain/. After the merger, vein and vain were homophones, and way and day had the same vowel.

The merged vowel was a diphthong, transcribed /ɛi/ or /æi/. Later (around the 17th century) 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 a front vowel:

and four ended in a back vowel:

Typical spellings are as in the examples above. The spelling ew is ambiguous between /ɪu/ and /ɛu/, and the spellings oi and oy are ambiguous between /ɔi/ and /ʊi/. The most common words with ew pronounced /ɛu/ were dew, few, hew, lewd, mew, newt, pewter, sew, shew (show), shrew, shrewd and strew. Words in which /ʊi/ 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 sixteenth century, the Great Vowel Shift had created two new diphthongs out of the former long close monophthongs /iː/ and /uː/ of Middle English. These diphthongs were /əɪ/ as in tide, and /əʊ/ as in house.[3] At this time, the English of south-eastern England could thus have had nine diphthongs.

By the end of the sixteenth century, the inventory of diphthongs was reduced as a result of several developments, all of which took place in the mid-to-late sixteenth century:[4]

This left /ɪu/, /ɔi/, /ʊi/, /əɪ/ and /əʊ/ as the diphthongs of south-eastern England.

17th century[]

By the end of the seventeenth century, the following further developments had taken place in the dialect of south-eastern England:[4]

As a result of these changes, there remained only the three diphthongs /aɪ/, /aʊ/ and /ɔɪ/.

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. This produced the vowels /eɪ/ and /oʊ/. In modern-day RP, the starting point of the latter diphthong has become more centralized, and the vowel 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 not followed by another vowel (see English-language vowel changes before historic /r/). These occur in words like near, square and cure.

Present-day RP, then, is 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[]

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 /ɛi, ɔu/ (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[6] as the long mid mergers.

Panepain merger[]

The panepain merger is a merger of the long mid monophthong /eː/ and the diphthong /ei/ that occurs in most dialects of English. In the vast majority of Modern English accents the vowels have been merged; whether the outcome is monophthongal or diphthongal depends on the accent. But in a few regional accents, including some in East Anglia, South Wales, and even Newfoundland, the merger has not gone through (at least not completely), so that pairs like pane/pain are distinct.

A distinction, with the pane words pronounced with [eː] and the pain words pronounced with [æɪ], survived in Norfolk English into the 20th century. Trudgill describes the disappearance of this distinction in Norfolk, saying that "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."[7]

Walters (2001)[8] reports the survival of the distinction in the Welsh English spoken in the Rhondda Valley, with [eː] in the pane words and [ɛi] in the pain words.

In accents that preserve the distinction, the phoneme /ei/ is usually represented by the spellings ai, ay, ei and ey as in day, play, rain, pain, maid, rein, they etc. and the phoneme /eː/ is usually represented by aCe as in pane, plane, lane, late etc. and sometimes by é and e as in re, café, Santa Fe etc.

Homophonous pairs
/eː/ /ei/ IPA
ade aid ˈeɪd
ale ail ˈeɪl
ate eight ˈeɪt[Note 1]
bale bail ˈbeɪl
blare Blair ˈbleə(r)
cane Cain ˈkeɪn
clade clayed ˈkleɪd
Clare Claire ˈkleə(r)
bate bait ˈbeɪt
Dane deign ˈdeɪn[Note 1]
daze days ˈdeɪz
e'er air ˈeə(r)
e'er heir ˈeə(r)
ere air ˈeə(r)
ere heir ˈeə(r)
fare fair ˈfeə(r)
faze fays ˈfeɪz
flare flair ˈfleə(r)
gale Gail ˈɡeɪl
gate gait ˈɡeɪt
gaze gays ˈɡeɪz
glave glaive ˈɡleɪv[Note 2]
grade grayed ˈɡreɪd
graze grays ˈɡreɪz
hale hail ˈheɪl
hare hair ˈheə(r)
haze hays ˈheɪz
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
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 1]
wale wail ˈweɪl
wales wails ˈweɪlz
Wales wails ˈweɪlz
wane wain ˈweɪn
waste waist ˈweɪst
wave waive ˈweɪv
waver waiver ˈweɪv
whale wail ˈweɪl[Note 3]

Toetow merger[]

The toetow merger is a merger of the Early Modern English vowels /oː/ (as in toe) and /ou/ (as in tow) that occurs in most dialects of English. (The vowels in Middle English and at the beginning of the Early Modern English period were /ɔː/ and /ɔu/ respectively, and they shifted in the second phase of the Great Vowel Shift.)

The merger occurs in the vast majority of Modern English accents; whether the outcome is monophthongal or diphthongal depends on the accent. The traditional phonetic transcription for General American and earlier Received Pronunciation in the 20th century is /oʊ/, a diphthong. But in a few regional accents, including some in Northern England, East Anglia and South Wales, the merger has not gone through (at least not completely), so that pairs like toe and tow, moan and mown, groan and grown, sole and soul, throne and thrown are distinct.

In 19th century England, the distinction was still very widespread; the main areas with the merger were in the northern Home Counties and parts of the Midlands.[9]

The distinction is most often preserved in East Anglian accents, especially in Norfolk. Peter Trudgill[7] 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,[10] young people in west Norfolk were found to be maintaining the distinction, with back [ʊu] or [ɤʊ] in the toe set and central [ɐʉ] in the tow set, with the latter but not the former showing the influence of Estuary English.

Walters[11] reports the survival of the distinction in the Welsh English spoken in the Rhondda Valley, with [oː] in the toe words and [ou] in the tow words.

Reports of Maine English in the 1970s reported a similar toad-towed distinction among older speakers, but was lost in subsequent generations.

In accents that preserve the distinction, the phoneme descended from Early Modern English /ou/ is usually represented by the spellings ou, and ow as in soul, dough, tow, know, though etc. or through L-vocalization as in bolt, cold, folk, roll etc., while that descended from Early Modern English /oː/ is usually represented by oa, oe, or oCe as in boat, road, toe, doe, home, hose, go, tone etc.

This merger did not occur before r originally, and only later occurred (relatively recently) as the horse–hoarse merger. This merger is not universal, however, and thusly words with our and oar may not sound the same as words with or in some dialects.

Homophonous 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
doe dough ˈdoʊ
does doughs ˈdoʊz
doze doughs ˈdoʊz
floe flow ˈfloʊ
foaled fold ˈfoʊld
fore four ˈfoə(r)
forth fourth ˈfoə(r)θ
fro frow ˈfroʊ
froe frow ˈfroʊ
froes frows ˈfroʊz
froze frows ˈfroʊz
groan grown ˈɡroʊn
holed hold ˈhoʊld
moan mown ˈmoʊn
mode mowed ˈmoʊd
Moe mow ˈmoʊ
no know ˈnoʊ
noes knows ˈnoʊz
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
roes rows ˈroʊz
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

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 also generally has a merger of /ɒ/ and /ɔː/, so that sets like "cot", "caught" and "coat" can be homophones.[12]

This merger can also be found in some broad Central Belt Scottish English accents.

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/.[13] Some other speakers may keep the contrast, so that rod is /rɑd/ and ride is /rad/. This merger requires the presence of the father-bother merger before it can occur.

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.[14]

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.[13]

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.[15]

Homophonous pairs
/aɪ/ /ɔɪ/ IPA
aisle oil ˈɑɪl
bile boil ˈbɑɪl
buy boy ˈbɑɪ
by boy ˈbɑɪ
bye boy ˈbɑɪ
dried droid ˈdrɑɪd
imply employ ɪmˈplɑɪ
file foil ˈfɑɪl
fire foyer ˈfɑɪə(r)[Note 4]
grind groined ˈɡrɑɪnd
guy goy ˈɡɑɪ
heist hoist ˈhɑɪst
I'll oil ˈɑɪl
isle oil ˈɑɪl
Jain join ˈdʒɑɪn
kine coin ˈkɑɪn
Kyle coil ˈkɑɪl
liar lawyer ˈlɑɪə(r)
lied Lloyd ˈlɑɪd
line loin ˈlɑɪn
Lyle loyal ˈlɑɪəl[Note 5]
lyre lawyer ˈlɑɪə(r)
pie poi ˈpɑɪ
pies poise ˈpɑɪz
pint point ˈpɑɪnt
psi soy ˈsɑɪ
ride roid ˈrɑɪd
rile roil ˈrɑɪl
rile royal ˈrɑɪəl[Note 5]
rye Roy ˈrɑɪ
sigh soy ˈsɑɪ
sire sawyer ˈsɑɪə(r)
sire soya ˈsɑɪə[Note 6]
Thai toy ˈtɑɪ
tide toyed ˈtɑɪd
tie toy ˈtɑɪ
tied toyed ˈtɑɪd
tile toil ˈtɑɪl
try Troy ˈtrɑɪ
vice voice ˈvɑɪs
vied void ˈvɑɪd
wry Roy ˈrɑɪ

Coilcurl merger[]

The coilcurl or oilearl merger is a vowel merger that historically occurred in some non-rhotic dialects of American English, due to an up-gliding NURSE vowel.

Maremayor merger[]

The maremayor merger is a process occurring in many varieties of British English, as well as the Philadelphia dialect and Baltimorese, where bisyllabic /eɪ.ə/ is pronounced as the centering diphthong /eə/ in many words. In these varieties, mayor is pronounced /ˈmeə(r)/, homophonous with mare.

In North American English accents with the merger, it also affects sequences without /r/, where some words with the /eɪ.ə/ sequence merge with /eə/ associated with æ-tensing. Because this particular /eə/ derived from /æ/, such words are frequently hypercorrected with /æ/. The best known examples of this are mayonnaise (/ˈmeəneɪz~ˈmæneɪz/) 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)

Face–near merger[]

The face–near merger is a variable and recessive merger of /eː/ and /iə/ (the vowels corresponding to /eɪ/ and /ɪə/ in RP) found in Geordie. It is not categorical, as FACE can instead be pronounced as the closing diphthong [eɪ] or, more commonly, the close-mid front monophthong []. The latter is the most common choice for younger speakers who tend to reject the centering diphthongs for /eː/, which categorically undoes the merger for those speakers.[16][17]

Even when FACE is realized as an opening-centering diphthong, it may be distinguished from NEAR by the openness of the first element: [ɪə] or [eə] vs. [iə].[18][19][20]

Homophonous pairs
/eː/ /iə/ IPA
face fierce ˈfiəs
hay here ˈhiə

Goat–cure merger[]

The goat–cure merger is a variable and recessive merger of /oː/ and /uə/ (the vowels corresponding to /əʊ/ and /ʊə/ in RP) found in Geordie. It is not categorical, as GOAT can instead be pronounced as the close-mid monophthongs [] and [ɵː]. The central [ɵː] is as stereotypically Geordie as the merger itself, though it is still used alongside [] by young, middle-class males who, as younger speakers in general, reject the centering diphthongs for /oː/. This categorically undoes the merger for those speakers.[16][21]

Even when GOAT is realized as an opening-centering diphthong, it may be distinguished from CURE by the openness of the first element: [ʊə] or [oə] vs. [uə].[18][19][20]

Homophonous pairs
/oː/ /uə/ IPA
toe tour ˈtuə
tow tour ˈtuə

See also[]


  1. ^ a b c With waitweight merger
  2. ^ Homonyms
  3. ^ With winewhine merger
  4. ^ Foyer may also be pronounced /ˈfɑɪeɪ/ or /ˈfwɑːjeɪ/.
  5. ^ a b With vilevial merger
  6. ^ Non-rhotic accents
  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. ^ Barber (1997), pp. 115–116
  6. ^ Wells (1982), pp. 192–194, 337, 357, 384–385, 498
  7. ^ a b "Norfolk England Dialect Orthography". Friends of Norfolk Dialect. Archived from the original on 2008-02-22. Retrieved 2019-02-13.
  8. ^ Walters (2001)
  9. ^ Britain (2001)
  10. ^ Britain (2002)
  11. ^ Walters (2001)
  12. ^ "Rodrik Wade, MA Thesis, Ch 4: Structural characteristics of Zulu English". Archived from the original on May 17, 2008. Retrieved 2008-05-17.CS1 maint: BOT: original-url status unknown (link)
  13. ^ a b Wells (1982), p. 557
  14. ^ Wells, John "Whatever happened to received pronunciation?" Wells: Whatever happened to received pronunciation? Author's webpage; accessed 19 April 2011.
  15. ^ Wells (1982), pp. 208–210
  16. ^ a b Watt & Allen (2003), p. 269.
  17. ^ Beal (2004), p. 123.
  18. ^ a b Watt (2000), p. 72.
  19. ^ a b Watt & Allen (2003), pp. 268–269.
  20. ^ a b Beal (2004), p. 126.
  21. ^ Beal (2004), pp. 123–124.