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

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:

• high, fully backing, /iu/ /iːu/, spelt ⟨io⟩ (found in Anglian dialects, but merged into /eo/ /eːo/ in Late West Saxon)
• high, narrower, possibly /iy/ /iːy/ or /ie/ /iːe/, spelt ⟨ie⟩ (found in Late West Saxon)
• mid, /eo/ /eːo/, spelt ⟨eo⟩
• low, /æɑ/ /æːɑ/, spelt ⟨ea⟩

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, 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:

• OE dæg ("day") and weg ("way") (where the /ɡ/ had been palatalized to /j/) became [dai] and [wɛi]
• OE clawu ("claw") and lagu ("law") became [klau] and [lau]

Diphthongs also arose as a result of [[Middle English breaking|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:

• OE streht ("straight") became [strɛiçt]
• OE þoht ("thought") became [θɔuxt]

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. 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, of which three ended in a front vowel:

• /ɛi/ as in nail, day, whey (the product of the vein–vain merger)
• /ɔi/ as in joy, noise, royal, coy
• /ʊi/ as in boil, destroy, coin, join

and four ended in a back vowel:

• /ɪu/ as in view, new, due, use, lute, suit, adieu (the product of a merger of earlier /iu/ and /eu/, also incorporating French loans that originally had /y/)
• /ɛu/ as in few, dew, ewe, shrewd, neuter, beauty
• /ɑu/ as in cause, law, salt, change, chamber, psalm, half, dance, aunt.
• /ɔu/ as in low, soul

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.

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. 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:

• /ɛu/ merged into /ɪu/ and so dew and due became homophones.
• /ɛi/ (from the vein–vain merger) became monophthongized and merged with the /ɛː/ of words like name (which before the Great Vowel Shift had been long /aː/). For more information, see pane–pain merger, below.
• /ɑu/, as in cause, became monophthongized to /ɔː/.
• /ɔu/, as in low, was monophthongized to /ɔː/. That would later rise to /oː/, which merged with the vowel of toe; see toe–tow merger, below.

That left /ɪu/, /ɔi/, /ʊi/, /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:

• The falling diphthong /ɪu/ of due and dew changed to a rising diphthong, which became the sequence [juː]. The change did not occur in all dialects, however; see Yod-dropping.
• The diphthongs /əɪ/ and /əʊ/ of tide and house widened to /aɪ/ and /aʊ/, respectively.
• The diphthong /ʊi/ merged into /aɪ/. Contemporary literature had frequent rhymes such as Mind–join'd in Congreve, join–line in Pope, child–spoil'd in Swift, toils–smiles in Dryden. The present-day pronunciations with /ɔɪ/ in the oi words result from regional variants, which had always had [ɔi], rather than [ʊi], perhaps because of influence by the spelling.

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

Later developments

In the 18th century or later, the monophthongs /eː/ and /oː/ (the products of the pane–pain and toe–tow 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 [[non-rhotic|loss of /r/]] when it is not followed by another vowel (see [[English-language vowel changes before historic /r/|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

Coil–curl merger

Main article: Rhoticity in English § Coil–curl merger

The coil–curl or oil–earl merger is a vowel merger that historically occurred in some non-rhotic dialects of American English, due to an up-gliding NURSE vowel.

Cot–coat merger

The cot–coat 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.

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

Line–loin merger

The line–loin 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.

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)
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
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
rye	Roy	ˈrɑɪ
sigh	soy	ˈsɑɪ
sire	sawyer	ˈsɑɪə(r)
sire	soya	ˈsɑɪə
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

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 pane–pain and toe–tow are homophones. These mergers are grouped together by Wells as the long mid mergers.

Pane–pain merger

The pane–pain 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."

Walters (2001) 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
bale	bail	ˈbeɪl
blare	Blair	ˈbleə(r)
cane	Cain	ˈkeɪn
clade	clayed	ˈkleɪd
Clare	Claire	ˈkleə(r)
bate	bait	ˈbeɪt
Dane	deign	ˈdeɪn
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
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
wale	wail	ˈweɪl
wales	wails	ˈweɪlz
Wales	wails	ˈweɪlz
wane	wain	ˈweɪn
waste	waist	ˈweɪst
wave	waive	ˈweɪv
waver	waiver	ˈweɪv
whale	wail	ˈweɪl

Toe–tow merger

The toe–tow 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.

The distinction is most often preserved in East Anglian accents, especially in Norfolk. Peter Trudgill 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, 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 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 thus 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
do (note)	dough	ˈdoʊ
doe	dough	ˈdoʊ
does	doughs	ˈdoʊz
dos	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

Mare–mayor merger

The mare–mayor 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/) and graham (/ˈɡreəm~ˈɡræm/, a homophone of gram).

Homophonous pairs

/eə/	/eɪə/	IPA
bare	Bayer	ˈbeə(r)
flare	flayer	ˈfleə(r)
flair	flayer	ˈfleə(r)
gram, gramme	Graham	ˈɡreəm
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)

Pride–proud merger

The pride–proud 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.

Rod–ride merger

The rod–ride 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/. Some other speakers may keep the contrast, so that rod is /rɑd/ and ride is /rad/.

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.

See also

• Phonological history of English
• Phonological history of English vowels
• Trisyllabic laxing
• Great Vowel Shift

References

Bibliography

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• Britain, David (2001). "Where did it all start? Dialect contact, the 'Founder Principle' and the so-called ⟨-own⟩ split in New Zealand English". Transactions of the Philological Society. 99 (1): 1–27. doi:10.1111/1467-968X.00072.
• Britain, David (2002). "Surviving 'Estuary English': innovation diffusion, koineisation and local dialect differentiation in the English Fenland". Essex Research Reports in Linguistics. 41: 74–103.
• Labov, William (1966). Social stratification of English in New York City. Washington, DC: Center for Applied Linguistics. ISBN 0-87281-149-2.
• Labov, William; Ash, Sharon; Boberg, Charles (2006). Atlas of North American English: Phonetics, Phonology and Sound Change: a Multimedia Reference Tool. Walter de Gruyter. ISBN 9783110167467.
• Wells, John C. (1982). Accents of English. Cambridge: Cambridge University Press. ISBN 0-521-24225-8.
• Walters, J. Roderick (2001). "English in Wales and a 'Welsh Valleys' accent". World English. 20 (3): 285–304. doi:10.1111/1467-971X.00216.
• Thomas, Erik R. (2006). Rural White Southern Accents (PDF). Walter de Gruyter. Archived from the original (PDF) on 2014-12-22. Retrieved 2015-08-26. {{cite book}}: |work= ignored (help)