Most dialects of modernEnglish have twoclosebackvowels: thenear-close near-back rounded vowel/ʊ/ found in words likefoot, and theclose back rounded vowel/uː/ (realized ascentral[ʉː] in many dialects) found in words likegoose. TheSTRUT vowel/ʌ/, which historically was back, is oftencentral[ɐ] as well. This article discusses the history of these vowels in various dialects of English, focusing in particular onphonemic splits and mergers involving these sounds.

TheOld English vowels included a pair of short and long close back vowels,/u/ and/uː/, bothwritten⟨u⟩ (the longer vowel is often distinguished as⟨ū⟩ in modern editions of Old English texts). There was also a pair of back vowels of mid-height,/o/ and/oː/, both of which were written⟨o⟩ (the longer vowel is often⟨ō⟩ in modern editions).

The same four vowels existed in theMiddle English system. The short vowels were still written⟨u⟩ and⟨o⟩, but long/uː/ came to be spelt as⟨ou⟩, and/oː/ as⟨oo⟩. Generally, the Middle English vowels descended from the corresponding Old English ones, butthere were certain alternative developments.

The Middle Englishopen syllable lengthening caused short/o/ to be mostly lengthened to/ɔː/ (an opener back vowel) inopen syllables, a development that can be seen in words likenose. During theGreat Vowel Shift, Middle English long/oː/ was raised to/uː/ in words likemoon; Middle English long/uː/ was diphthongised, becoming the present-day/aʊ/, as inmouse; and Middle English/ɔː/ ofnose was raised and later diphthongized, leading to present-day/oʊ~əʊ/.

At some point, short/u/ developed into alax,near-close near-back rounded vowel,/ʊ/, as found in words likeput. (Similarly,short/i/ has become/ɪ/.) According to Roger Lass, the laxing occurred in the 17th century, but other linguists have suggested that it may have taken place much earlier.^[1] The short/o/ remaining in words likelot has also been lowered and, in some accents, unrounded (seeopen back vowels).

In a handful of words, some of which are very common, the vowel/uː/ was shortened to/ʊ/. In a few of those words, notablyblood andflood, the shortening happened early enough that the resulting/ʊ/ underwent the "foot–strut split" (see next section) and are now pronounced with/ʌ/. Other words that underwent shortening later consistently have/ʊ/, such asgood andfoot. Still other words, such asroof,hoof, androot, are variable, with some speakers preferring/uː/ and others preferring/ʊ/ in such words, such as inTexan English. For some speakers in Northern England, words ending in-ook that have undergone shortening to/ʊ/ elsewhere, such asbook andcook, still have the long/uː/ vowel.

TheFOOT–STRUT split is the split ofMiddle English short/u/ into two distinct phonemes:/ʊ/ (as infoot) and/ʌ/ (as instrut). The split occurs in most varieties of English, the most notable exceptions being most ofNorthern England and theEnglish Midlands and some varieties ofHiberno-English.^[2] InWelsh English, the split is also absent in parts ofNorth Wales under influence fromMerseyside andCheshire accents^[3] and in the south ofPembrokeshire, where English overtook Welsh long before that occurred in the rest of Wales.^[4]

The origin of the split is the unrounding of/ʊ/ inEarly Modern English, resulting in the phoneme/ʌ/. Usually, unrounding to/ʌ/ did not occur if/ʊ/ was preceded by alabial consonant, such as/p/,/f/,/b/, or was followed by/l/,/ʃ/, or/tʃ/, leaving the modern/ʊ/. Because of the inconsistency of the split,put andputt became aminimal pair that were distinguished as/pʊt/ and/pʌt/. The first clear description of the split dates from 1644.^[5]

In non-splitting accents,cut andput rhyme,putt andput are homophonous as/pʊt/, andpudding andbudding rhyme. However,luck andlook may not necessarily be homophones since many accents in the area concerned havelook as/luːk/, with the vowel ofgoose.

The absence of the split is a less common feature of educated Northern English speech than the absence of thetrap–bath split. The absence of the foot–strut split is sometimes stigmatized,^[6] and speakers of non-splitting accents may try to introduce it into their speech, which sometimes results inhypercorrection such as by pronouncingbutcher/ˈbʌtʃər/.^[7]

InBirmingham and theBlack Country, the realisation of theFOOT andSTRUT vowels is somewhat like a neutralisation between Northern and Southern dialects.FOOT may be pronounced with a/ɤ/, andSTRUT may be pronounced with a/o/. However, both may also be pronounced with a phonetically intermediate/ɤ/^[8] which is also present further north inTyneside.^[9] There is also variation in some non-splitting dialects, as while most words use/ʊ/, some words such asnone,one,once,nothing,tongue andamong(st) may instead be pronounced with/ɒ/ in dialects such as parts ofYorkshire.^[10]

The nameFOOT–STRUT split refers to thelexical sets introduced byWells (1982) and identifies the vowel phonemes in the words. From a historical point of view, however, the name is inappropriate because the wordfoot did not have short/ʊ/ when the split happened, but it underwent shortening only later.

In modern standard varieties of English, such asReceived Pronunciation (RP) andGeneral American (GA), theFOOT vowel/ʊ/ is a relatively uncommon phoneme. It occurs most regularly in words in-ook (likebook, cook, hook etc.). It is also spelt-oo- infoot, good, hood, soot, stood, wood, wool, and-oul- incould, should, would. Otherwise, it is spelt-u- (but-o- afterw-); such words includebull, bush, butcher, cushion, full, pudding, pull, push, puss, put, sugar, wolf, woman. More frequent use is found in recent borrowings though sometimes in alternation withSTRUT (as inMuslim in both RP/GA) orGOOSE (as inBuddha in GA).

TheSTRUT–COMMA merger or theSTRUT–schwa merger is a merger of/ʌ/ with/ə/ that occurs inWelsh English, some higher-prestigeNorthern England English and some General American. The merger causesminimal pairs such asunorthodoxy/ʌnˈɔːrθədɒksi/ andan orthodoxy/ənˈɔːrθədɒksi/ to be merged.^{[citation needed]} The phonetic quality of the merged vowel depends on the accent. For instance, merging General American accents have[ʌ] as the stressed variant and[ɐ] as the word-final variant. Elsewhere, the vowel surfaces as[ə] or even[ɪ̈] (GA features theweak vowel merger). That can cause words such ashubbub (/ˈhʌbʌb/ in RP) to have two different vowels ([ˈhʌbəb]) even though both syllables contain the same phoneme in both merging and non-merging accents. On the other hand, some areas likeBirmingham in England and much ofWales have no noticeable difference between the stressed and the unstressed allophones, and at least the non-final variant of the merged vowel is consistently realized as the mid and central[ə] (rather than open-mid).^[11][12][13]

The merged vowel is typically written with ⟨ə⟩ regardless of its phonetic realization. That largely matches an older canonical phonetic range of the IPA symbol ⟨ə⟩, which used to be described as covering a vast central area from near-close[ɪ̈] to near-open[ɐ].^[14]

Because in unmerged accents,/ə/ appears only in unstressed syllables, the merger occurs only in unstressed syllables. Word-finally, there is no contrast between the vowels in any accent of English (inMiddle English,/u/, the vowel from which/ʌ/was split, could not occur in that position), and the vowel that occurs in that position approaches[ɐ] (the main allophone ofSTRUT in many accents). However, there is some dialectal variation, with varieties such as broadCockney using variants that are strikingly more open than in other dialects. The vowel is usually identified as belonging to the/ə/ phoneme even in accents without the/ʌ–ə/ merger, but native speakers may perceive the phonemic makeup of words such ascomma to be/ˈkɒmʌ/, rather than/ˈkɒmə/.^[15][16] The open variety of/ə/ occurs even in some Northern English dialects (such asGeordie), none of which has undergone the foot–strut split, but in Geordie, it can be generalised to other positions and so not onlycomma but alsocommas may be pronounced with[ɐ] in the second syllable, which is rare in other accents.^[17] In contemporary Standard Southern British English, the final/ə/ is often mid[ə], rather than open[ɐ].^[18]

All speakers of General American neutralise/ʌ/,/ə/ and/ɜː/ (theNURSE vowel) before/r/, which results in anr-colored vowel[ɚ]. GA lacks a truly contrastive/ɜː/ phoneme (furry,hurry,letters andtransfer (n.), which are distinguished in RP as/ɜː/,/ʌ/,/ə/ and/ɜː/, all have the same r-colored[ɚ] in GA), and the symbol is used only to facilitate comparisons with other accents.^[19] Seehurry–furry merger for more information.

Some other minimal pairs apart fromunorthodoxy–an orthodoxy includeunequal/ʌnˈiːkwəl/ vs.an equal/ənˈiːkwəl/ anda large untidy room/əˈlɑːrdʒʌnˈtaɪdiˈruːm/ vs.a large and tidy room/əˈlɑːrdʒənˈtaɪdiˈruːm/. However, there are few minimal pairs like that, and their use as such has been criticised by scholars such asGeoff Lindsey because the members of such minimal pairs are structurally different. Even so, pairs of words belonging to the same lexical category exist as well such asappend/əˈpɛnd/ vsup-end/ʌpˈɛnd/ andaneath/əˈniːθ/ vsuneath/ʌnˈiːθ/. There also are words for which RP always used/ʌ/ in the unstressed syllable, such aspick-up/ˈpɪkʌp/,goosebumps/ˈɡuːsbʌmps/ orsawbuck/ˈsɔːbʌk/, that have merging accents use the same/ə/ as the second vowel ofbalance. In RP, there is a consistent difference in vowel height; the unstressed vowel in the first three words is a near-open[ɐ] (traditionally written with ⟨ʌ⟩) but inbalance, it is a mid[ə].^[13][18][20]

EarlierMiddle English distinguished theclose front rounded vowel/yː/ (occurring in loanwords fromAnglo-Norman likeduke) and thediphthongs/iw/ (occurring in words likenew),/ew/ (occurring in words likefew)^[21] and/ɛw/ (occurring in words likedew).

By Late Middle English,/yː/,/ew/, and/iw/all merged as/ɪw/. In Early Modern English,/ɛw/ merged into/ɪw/ as well.

/ɪw/ has remained as such in some Welsh, some northern English and a few American accents. Thus, those varieties of Welsh English keepthrew/θrɪw/ distinct fromthrough/θruː/. In most accents, however, thefalling diphthong/ɪw/ turned into a rising diphthong, which became the sequence/juː/. The change had taken place in London by the late 1800s. Depending on the preceding consonant and on the dialect, it either remained as/juː/ or developed into/uː/ by the processes ofyod-dropping oryod-coalescence.^[22] That has caused the standard pronunciations ofduke/d(j)uːk/ (or/dʒuːk/),new/n(j)uː/,few/fjuː/ andrude/ruːd/.

TheFOOT–GOOSE merger is a phenomenon inScottish English,Northern Irish English,Malaysian English, andSingapore English,^{[23][full citation needed]} in which the modern English phonemes/ʊ/ and/uː/ have merged into a single phoneme. As a result, word pairs likelook andLuke,pull andpool,full andfool are homophones, and pairs likegood andfood andfoot andboot rhyme.

The history of the merger dates back to twoMiddle English phonemes: the long vowel/oː/ (whichshoot traces back to) and the short vowel/u/ (whichput traces back to). As a result of theGreat Vowel Shift,/oː/ raised to/uː/, which continues to be the pronunciation ofshoot today. Meanwhile, the Middle English/u/ later adjusted to/ʊ/, asput is pronounced today. However, the/uː/ ofshoot next underwent aphonemic split in which some words retained/uː/ (likemood) while the vowel of other words shortened to/ʊ/ (likegood). Therefore, the two processes (/oː/→/uː/→/ʊ/ and/u/→/ʊ/) resulted in a merger of the vowels in certain words, likegood andput, to/ʊ/, which is now typical of how all English dialects pronounce those two words. (See the table in the section "FOOT–STRUT split" above for more information about these early shifts.)^{[note 1]} The final step, however, was for certain English dialects under the influence of foreign languages (theScots language influencing Scottish English, for example)^{[citation needed]} to merge the newly united/ʊ/ vowel with the/uː/ vowel (ofmood andshoot): theFOOT–GOOSE merger. Again, this is not an internally motivated phonemic merger but the appliance of different languages' vowel systems to English lexical incidence.^{[24][full citation needed]} The quality of this final merged vowel is usually[ʉ~y~ʏ] in Scotland and Northern Ireland but[u] in Singapore.^[25]

Thefull–fool merger is a conditioned merger of the same two vowels specifically before/l/, which causes pairs likepull/pool andfull/fool to be homophones; it appears in many other dialects of English and is particularly gaining attention in severalAmerican English varieties.

InGeordie, theGOOSE vowel undergoes an allophonic split, with the monophthong[uː~ʉː] being used in morphologically-closed syllables (as inbruise[bɹuːz~bɹʉːz]) and the diphthong[ɵʊ] being used in morphologically-open syllables word-finally (as inbrew[bɹɵʊ]) but also word-internally at the end of amorpheme (as inbrews[bɹɵʊz]).^[17][26]

Most dialects of English turn/uː/ into a diphthong, and the monophthongal[uː~ʉː~ɨː] is infree variation with the diphthongal[ʊu~ʊ̈ʉ~əʉ~ɪ̈ɨ], particularly word-internally. Word-finally, diphthongs are more usual. Compare theidentical development of the close frontFLEECE vowel.

The change of/uː.ɪ/ to[ʊɪ] is a process that occurs in many varieties ofBritish English in which bisyllabic/uː.ɪ/ has become the diphthong[ʊɪ] in certain words. As a result, "ruin" is pronounced as monosyllabic[ˈɹʊɪn] and "fluid" is pronounced[ˈflʊɪd].^[27]

• Phonological history of English
• Phonological history of English vowels
• Phonological history of English consonants
• Phonological history of English consonant clusters § Yod-dropping

• Splits and mergers in English phonology

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