Phonological history of English diphthongs
Note: This article deals with sound changes involving English-language diphthongs. Each of the following sound changes involved at least one phoneme which historically was a diphthong. The sound changes discussed here may also have involved a phoneme which was historically or is now a monophthong. For sound changes involving English-language centering diphthongs see English-language vowel changes before historic r.
Vein–vain merger 
As a result of the merger, vein and vain are now homophones, but in early Middle English they were pronounced differently as /ˈvein/ and /ˈvain/. Similarly day (from Old English dæġ) and way (from Old English weġ) did not rhyme before the merger.
The merged vowel was a diphthong, often transcribed /ɛi/. It later merged (in most dialects) with the /eː/ of words like pane in the pane–pain merger.
Diphthongs of Late Middle English 
The English of South-Eastern England in about 1400 had seven diphthongs:
With front endpoint:
- /aɪ/ as in nail, day, eight, whey
- /ɔɪ/ as in joy, noise, royal, coy
- /ʊɪ/ as in boil, destroy, coin, join
With back endpoint:
- /ɪu/ as in view, new, due, use, lute, suit, adieu
- /ɛʊ/ as in few, dew, ewe, shrewd, neuter, beauty
- /aʊ/ as in cause, caught, thought, law, salt, change, chamber, psalm, half, dance, aunt.
- /ɔʊ/ as in low, soul
Typical spellings are as in the examples above. The spelling Cew (where C represents any consonant) is ambiguous between /ɪu/ and /ɛʊ/, and the spellings oi and oy are ambiguous between /ɔɪ/ and /ʊɪ/. The most common words with Cew pronounced /ɛʊ/ were dew, few, hew, lewd, mew, newt, pewter, sew, shew ("show"), shrew, shrewd and strew. Words in which /ʊɪ/ was commonly used included boil, coin, destroy, join, moist, point, poison, soil, spoil, Troy, turmoil and voice, although there was significant variation.
Great Vowel Shift 
By the mid sixteenth century, the Great Vowel Shift had created two new diphthongs out of what were formerly close long vowels of Middle English. These were /əɪ/ as in tide, and /əʊ/ as in house. At this period, the English of South-Eastern England could thus have had nine diphthongs.
Late sixteenth century 
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:
- the merger of /ɛu/ with /iʊ/, resulting in dew becoming homophonous with due.
- the pane–pain merger, by which /aɪ/, having become raised to /ɛɪ/, merged with /ɛː/
- the monophthonging of /aʊ/ to /ɒː/
- the monophthonging of /ɔʊ/ to /ɔː/
This left /iu/, /ɔɪ/, /ʊi/, /əɪ/ and /əʊ/ as the diphthongs of South-Eastern England.
Late seventeenth century 
By the end of the seventeenth century, the following further developments had taken place in the dialect of South-Eastern England:
- the tow–toe merger, by which /ɔʊ/, having already been monophthongized to /ɔː/ was raised to /oː/.
- the /iʊ/ of due/dew changed from a falling to a rising diphthong, the result usually being written /juː/ and often analysed as a glide rather than a true diphthong.
- the diphthongs /əɪ/ and /əʊ/ widen to /aɪ/ and /aʊ/ respectively
- the diphthong /ʊi/ merges with /aɪ/. In literature from this period there frequently occur rhymes such as "Mind/join'd" (Congreve), "join/line" (Pope), "child/spoil'd" (Swift), "toils/smiles" (Dryden). The present-day pronunciations with /ɔɪ/ in these words result from regional variants which had always had /ɔɪ/ rather than /ʊi/, perhaps influenced by the spelling.
As a result of these changes, there remained only the three diphthongs /aɪ/, /aʊ/ and /ɔɪ/
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."
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 eCe and e as in re, cafe, Santa Fe etc.
Toe–tow merger 
The toe–tow merger is a merger of the post-Early Modern English vowels /oː/ (as in toe) and /ou/ (as in tow) that occurs in most dialects of English. (The vowels in Early Modern English itself were /ɔː/ and /ɔu/ respectively, but this changed with 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.
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 [ʊu] or [ɤʊ] in the toe set and a fronted [ɐʉ] in the tow set, with the latter but not the former showing the influence of Estuary English.
In accents that preserve the distinction, the phoneme descended from Early Modern English /ɔu/ 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 /ɔː/ is usually represented by oa, oe, or oCe as in boat, road, toe, doe, home, hose, go, tone etc.
Cot–coat merger 
The cot–coat merger is phenomenon occurring for some speakers of Zulu English where 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.
Poet smoothing 
|This section does not cite any references or sources. (November 2006)|
Poet smoothing is a process occurring in many varieties of British English where bisyllabic /əʊ.ə/ is pronounced as the diphthong [ɜɪ] in many words. In these varieties, "poet" is pronounced as monosyllabic [ˈpɜɪt] and "poem" is pronounced [ˈpɜɪm].
Rod–ride merger 
The rod–ride merger is a merger of /ɑ/ and /aɪ/ occurring for some speakers of African American Vernacular English (AAVE), in which rod and ride are merged as /rɑd/. Some other speakers of AAVE may keep the contrast, so that rod is /rɑd/ and ride is /rad/.
Scientific smoothing 
Scientific smoothing 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 /saɪən.ˈtɪf.ɪk/ with three syllables and "science" is pronounced /ˈsaɪəns/ with one syllable.
Pride–proud merger 
The pride–proud merger is a merger of the diphthongs /aɪ/ and /aʊ/ before voiced consonants into monophthongal /ä/ 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 /ɑː/, /aɪ/ and /aʊ/ before voiced consonants, making pride, prod, and proud and find, found and fond homophones.
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/loin, bile/boil, imply/employ are homophones in merging accents.
Coil–curl merger 
The merger caused the vowel classes associated with the General American phonemes /ɔɪ/, as in choice, and /ɝ/, as in nurse, to merge, making coil and curl homophones. The merged vowel was typically a diphthong [ɜɪ], with a mid-central starting point, rather than the back rounded starting point of /ɔɪ/ in most other accents of English. The merger happened only before a consonant; stir and boy never rhymed.
The merger is responsible for the "Brooklynese" stereotypes of bird sounding like "boid" and thirty-third sounding like "toity-toid".
According to a survey that was done by William Labov in New York in 1966, 100% of the people over 60 used [ɜɪ] for bird. With each younger age group, however, the percentage got progressively lower: 59% of 50-59 year olds, 33% of 40-49 year olds, 24% of 20-39 year olds, and finally, only 4% of people 8–19 years old used [ɜɪ]. Nearly all native New Yorkers born since 1950, even those whose speech is otherwise non-rhotic, now pronounce bird as [ˈbɝd].
Mare–mayor merger 
|This section does not cite any references or sources. (November 2006)|
The mare–mayor 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 central diphthong /eə/ in many words. In these varieties, "mayor" is pronounced /ˈmeə/, 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).
- Wells, John C. (1982). Accents of English. Cambridge: Cambridge University Press. p. 192. ISBN 0-521-24225-8.
- Barber, pp. 112-116
- Barber, p. 108
- Barber, pp. 108, 116
- Barber, pp. 115-116
- Wells, ibid., 192–94, 337, 357, 384–85, 498
- Norfolk England Dialect Orthography
- Walters, J. R. (2001). "English in Wales and a 'Welsh Valleys' accent". World English 20: 283–304.
- Britain, D. (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: 1–27. doi:10.1111/1467-968X.00072.
- Britain, D. (2002). "Surviving 'Estuary English': Innovation diffusion, koineisation and local dialect differentiation in the English Fenland" (PDF). Essex Research Reports in Linguistics 41: 74–103.
- Walters, ibid.
- Rodrik Wade, MA Thesis, Ch 4: Structural characteristics of Zulu English at the Wayback Machine (archived May 17, 2008)
- Wells, ibid., 557
- Wells, John "Whatever happened to received pronunciation?" Wells: Whatever happened to received pronunciation? Author's webpage; accessed 19 April 2011.
- Wells, ibid., 208–10
- Wells, ibid., 508 ff.
- Labov, William (1966). Social stratification of English in New York City. Washington, D.C.: Center for Applied Linguistics. ISBN 0-87281-149-2.
- Barber, Charles Laurence (1997). Early modern English (second ed.). Edinburgh: Edinburgh University Press. ISBN 0-7486-0835-4.
See also 
- Phonological history of the English language
- Phonological history of English vowels
- Trisyllabic laxing
- Great Vowel Shift