In English, many vowel shifts affect only vowels followed by /r/ in rhotic dialects, or vowels that were historically followed by an /r/ that has since been elided in non-rhotic dialects. Most of them involve merging of vowel distinctions, so that fewer vowel phonemes occur before /r/ than in other positions in a word.
In rhotic dialects, /r/ is pronounced in most cases. In General American (GA), /r/ is pronounced as an approximant or in most positions, but after some vowels is pronounced as r-coloring. In Scottish English, /r/ is traditionally pronounced as a flap or trill , and there are no r-colored vowels.
In non-rhotic dialects like Received Pronunciation (RP), historic /r/ is elided at the end of a syllable, and if the preceding vowel is stressed, it undergoes compensatory lengthening or breaking (diphthongization). Thus, words that historically had /r/ often have long vowels or centering diphthongs ending in a schwa /?/, or a diphthong followed by a schwa.
In most English dialects, there are vowel shifts that affect only vowels before /r/, or vowels that were historically followed by /r/. Vowel shifts before historical /r/ fall into two categories: mergers and splits. Mergers are more common, and therefore most English dialects have fewer vowel distinctions before historical /r/ than in other positions in a word.
In many North American dialects, there are ten or eleven stressed monophthongs; only five or six vowel (rarely, seven) contrasts are possible before a following /r/ in the same syllable (beer, bear, burr, bar, bore, bor, boor). Often, more contrasts exist when the /r/ is not in the same syllable; in some American dialects and in most native English dialects outside North America, for example, mirror and nearer do not rhyme, and some or all of marry, merry and Mary are pronounced distinctly. (In North America, these distinctions are most likely to occur in New York City, Philadelphia, some of Eastern New England (for some, including Boston), and in conservative Southern accents.) In many dialects, however, the number of contrasts in this position tends to be reduced, and the tendency seems to be towards further reduction. The difference in how these reductions have been manifested represents one of the greatest sources of cross-dialect variation.
Non-rhotic accents in many cases show mergers in the same positions as rhotic accents do, even though there is often no /r/ phoneme present. This results partly from mergers that occurred before the /r/ was lost, and partly from later mergers of the centering diphthongs and long vowels that resulted from the loss of /r/.
In some cases, the quality of a vowel before /r/ is different from the quality of the vowel elsewhere. For example, in some dialects of American English the quality of the vowel in more typically does not occur except before /r/, and is somewhere in between the vowels of maw and mow. It is similar to the vowel of the latter word, but without the glide.
It is important to note however that different mergers occur in different dialects. Among United States accents, the Boston, Eastern New England and New York accents have the lowest degree of pre-rhotic merging. Some have observed that rhotic North American accents are more likely to have such merging than non-rhotic accents, but this cannot be said of rhotic British accents like Scottish English, which is firmly rhotic and yet many varieties have all the same vowel contrasts before /r/ as before any other consonant.
Most North American English dialects merge the lax vowels with the tense vowels before /r/. "marry" and "merry" have the same vowel as "mare", "mirror" has the same vowel as "mere", "forest" has the same vowel as the stressed form of "for", and "hurry" has the same vowel as "stir" for these speakers. These mergers are typically resisted for nonrhotic North Americans and are largely absent in areas of the United States that were historically largely nonrhotic.
The hurry-furry merger occurs when the vowel /?/ before intervocalic /r/ is merged with /?/, particularly a feature in most dialects of North American English, although it is resisted in New York City English, Mid-Atlantic American English, older Southern American English, and some speakers of Eastern New England English.[clarification needed] Speakers with this merger pronounce hurry so that it rhymes with furry, and turret so that it rhymes with stir it.
British English and most other English outside of North America maintains the distinction between these two sounds, so that in their dialects, hurry and furry do not rhyme.
In General American there is a three-way merger between the first vowels in hurry and furry as well as the unstressed vowel in letters. In RP, all of these have different sounds (/?/, /?:/ and /?/, respectively) and there exist some minimal pairs between unstressed /?:/ and /?/, such as foreword /'f?:w?:d/ vs. forward /'f?w?d/. In GA, these collapse to ['f?rw?d], though in phonemic transcription they can still be differentiated as /'f?rw?rd/ and /'f?rw?rd/ to facilitate comparisons with other accents. Furthermore, GA often lacks a proper opposition between /?/ and /?/, which makes minimal pairs such as unorthodoxy and an orthodoxy variably homophonous as /?n'?rd?ksi/. See strut-comma merger for more information.
In New Zealand English there is a consistent contrast between hurry and furry, but the unstressed /?/ is lengthened to /?:/ (phonetically ) in many positions (particularly in formal or slow speech), especially when it is spelled ⟨er⟩. Thus, boarded and bordered might be distinguished as /'b?:d?d/ and /'b?:d?:d/ (homophonous in Australia as /'b?:d?d/ and distinguished in RP as /'b?:d?d/ and /'b?:d?d/), based on length and rounding of /?:/. This change was caused by a complete phonemic merger of /?/ and /?/, a weak vowel merger generalized to all environments.
|furrier (n.)||furrier (adj.)||/'f?ri?r/|
One notable merger of vowels before /r/ is the Mary-marry-merry merger, which consists of a merging of the vowels /æ/ (as in the name Carrie or the word marry) and /?/ (as in Kerry or merry) with historical /e?/ (as in Cary or Mary) whenever they are realised before intervocalic /r/ (the "r" sound when occurring between vowels). No contrast exist before a final or preconsonantal /r/. This merger is fairly widespread, in that it is complete or at a near-complete stage in most varieties of North American English,[sample 1] but rare in other varieties of English. The following variants are common in North America:
The three are kept distinct outside of North America. In accents that do not have the merger, Mary has the a sound of mare, marry has the "short a" sound of mat, and merry has the "short e" sound of met. In modern RP, they are pronounced as ['m?:?i], ['mæ?i], and ['mi]; in Australian English as ['me:?i], ['mæ?i], and ['me?i]; in New York City English as ['me?i?'mi], ['mæ?i], and ['mi]; in Philadelphia English, the same as New York, except merry is ['mi?'mi]. There is plenty of variance in the distribution of the merger, with expatriate communities of these speakers being formed all over the country.
The Mary-merry merger is possible in New Zealand English, in which the quality of the merged vowel is (similar to KIT in General American). However, in NZE, the vowel in Mary often merges with the NEAR vowel /i?/ instead (see near-square merger), which before intervocalic /r/ may in turn merge with /i:/, so that Mary (phonemically /'mei/) can be ['mii] or ['mi:?i] instead. In all of those cases there is a clear distinction between Mary and merry on one hand (however they are pronounced) and marry /'m?ri/ (with the TRAP vowel) on the other.
|Aaron1||Aaron2||Erin||'?r?n||with weak-vowel merger|
|-||barrel||beryl||'b?r?l||with weak-vowel merger before /l/|
|-||Farrell||feral||'f?r?l||with weak-vowel merger before /l/|
The merry-Murray merger (sometimes called the ferry-furry merger, but that is the case only for speakers who also have the hurry-furry merger) is a merger of /?/ and /?/ before /r/ (both neutralized with syllabic r) that is common in the Philadelphia accent. This accent does not usually have the marry-merry merger. That is, "short a" /æ/ as in marry is a distinct unmerged class before /r/. Thus, merry and Murray are pronounced the same, but marry is distinct from this pair.
Another widespread merger is the mirror-nearer merger or Sirius-serious merger of /?/ with /i/ before intervocalic /r/ (in other words, the sound "r" when between vowels). The typical result of the merger in General American is [?r] or [r]. For speakers with this merger, common in general accents throughout North America, mirror and nearer rhyme, and Sirius is homophonous with serious. North Americans who do not merge these vowels often speak the more conservative northeastern or southern accents.
Words that would have a stressed /?/ before intervocalic /r/ in the UK's Received Pronunciation (RP) are treated differently in different varieties of North American English. As shown in the table below, in Canadian English, all of these are pronounced with [-?r-], as in cord. In the accents of Philadelphia, southern New Jersey, and the Carolinas (and traditionally throughout the South), these words are pronounced among some with [-?r-], as in card (and thus merge with historic prevocalic /?r/ in words like starry). In the accents of New York City, Long Island, and nearby parts of New Jersey, these words are pronounced with [?r] like in RP. However, this is met with hypercorrection of /?r/, (thus still merging with historic prevocalic /?r/ in starry). On the other hand, the traditional Eastern New England accents (famously, the Rhode Island and Boston accents) these words are pronounced with [-?r-], but that [?] is a free vowel (the outcome of the cot-caught merger) and in that regard it is the same as Canadian /?/, rather than RP /?/. Most of the rest of the United States (marked "General American" in the table), however, has a distinctive mixed system: while the majority of words are pronounced as in Canada, the four (sometimes five) words in the left-hand column are typically pronounced with [-?r-]; and the East Coast regions seem to be slowly moving toward this system over time.
In accents with the horse-hoarse merger, /?r/ also includes the historic /o?r/ in words such as glory and force. When an accent also features the cot-caught merger, /?r/ is typically analyzed as /o?r/ to avoid postulating a separate /?/ phoneme that occurs only before /r/, so that both cord and glory are considered to contain the /o?/ phoneme in California, Canada and other places. Therefore, in the horse-hoarse merged accents /k?rd/ and /ko?rd/ are different analyses of the same word cord and there may be little to no difference in the realization of the vowel.
|LOT and THOUGHT before prevocalic /r/ by dialectExample words with|
|Pronounced /?r/ in RP and /?r/ or /?r/ in eastern coastal American English||Pronounced /?:r/ in RP and /?r/ in eastern coastal American English|
|Pronounced /or/ in Canadian English|
|Pronounced /?r/ in General American||Pronounced /?r/ in General American|
|only these four or five words:
||Words containing /?r/ in RP:
||Words containing /?:r/ in RP:
Even in the East Coast accents of the United States without the split (Boston, New York City, Rhode Island, Philadelphia, and some coastal Southern), some of the words in the original short-o class often show influence from other American dialects and end up with [-?r-] anyway. For instance, some speakers from the Northeast pronounce Florida, orange, and horrible with [-?r-], but foreign and origin with [-?r-]. Exactly which words are affected by this differs from dialect to dialect and occasionally from speaker to speaker, an example of sound change by lexical diffusion.
The Middle English merger of the vowels with the spellings ⟨our⟩ and ⟨ower⟩ now affects all modern varieties of English that makes words like sour and hour, which originally had one syllable, have two syllables, and thus rhyme with power. In accents that lack the merger, sour has one syllable and power has two syllables. Similar mergers also occur where 'hire' gains a syllable making it homophonous with 'higher', and 'coir' gains a syllable making it homophonous with 'coyer'.
The card-cord merger or cord-card merger is a merger of Early Modern English [?r] with [?r], resulting in homophony of pairs like card/cord, barn/born and far/for. It is roughly similar to the father-bother merger but before r. The merger is found in some Caribbean English accents, in some versions of the West Country accent in England and in some accents of Southern American English. Areas of the United States in which the merger is most common include Central Texas, Utah, and St. Louis, but it is not dominant even there, and it is rapidly disappearing. In the United States, dialects with the card-cord merger are some of the only ones without the horse-hoarse merger, with a well-documented correlation. 
In Modern English dialects, the reflexes of Early Modern English /u:r/ and /iur/ are highly susceptible to phonemic merger with other vowels. Words belonging to this class are most commonly spelled with oor, our, ure, or eur; examples include poor, tour, cure, Europe (words such as moor ultimately from Old English ? words). Wells refers to this class as the cure words, after the keyword of the lexical set to which he assigns them.
In traditional Received Pronunciation and General American, cure words are pronounced with RP // (/r/ before a vowel) and GenAm /?r/. But these pronunciations are being replaced by other pronunciations in many English accents.
In southern England English it is now common to pronounce cure words with /?:/, so that moor is often pronounced /m?:/, tour /t?:/, poor /p?:/. The traditional form is much more common in the northern counties of England. A similar merger is encountered in many varieties of American English, where the pronunciations [o?] or [or]?[?r] (depending on whether the accent is rhotic or non-rhotic) prevail. For many American English speakers historical /u:r/ merges with either /?r/ when it follows palatal consonants in words like "cure", "sure", "pure" and "mature" or /?r/ in other environments such as words like "poor" and "moor".
In Australian and New Zealand English the centring diphthong // has practically disappeared, replaced in some words by /?:?/ (a sequence of two separate monophthongs) and in some by /o:/ (a long monophthong). The outcome that occurs in a particular word is not always predictable, but, for example, pure, cure and tour come to rhyme with fewer, having /?:?/, while poor, moor and sure come to rhyme with for and paw, having /o:/.
|boor||boar||'b?:(r)||With horse-hoarse merger.|
|boor||Boer||'b?:(r)||With horse-hoarse merger.|
|boor||bore||'b?:(r)||With horse-hoarse merger.|
|gourd||gored||':(r)d||With horse-hoarse merger.|
|lure||law||'l?:||Non-rhotic with yod-dropping.|
|lure||lore||'l?:(r)||With horse-hoarse merger and yod-dropping.|
|lured||laud||'l?:d||Non-rhotic with yod-dropping.|
|lured||lawed||'l?:d||Non-rhotic with yod-dropping.|
|moor||more||'m?:(r)||With horse-hoarse merger.|
|poor||pore||'p?:(r)||With horse-hoarse merger.|
|poor||pour||'p?:(r)||With horse-hoarse merger.|
|sure||shore||':(r)||With horse-hoarse merger.|
|tour||tore||'t?:(r)||With horse-hoarse merger.|
|toured||toward||'t?:d||Non-rhotic with horse-hoarse merger.|
|whored||hoard||'h?:(r)d||With horse-hoarse merger. whored also has an alternative pronunciation that is already a perfect homophone of hoard.|
|whored||horde||'h?:(r)d||With horse-hoarse merger. whored also has an alternative pronunciation that is already a perfect homophone of horde.|
|your||yore||'j?:(r)||With horse-hoarse merger.|
|you're||yore||'j?:(r)||With horse-hoarse merger.|
In East Anglia a cure-nurse merger in which words like fury merge to the sound of furry [?:] is common, especially after palatal and palatoalveolar consonants, so that sure is often pronounced [:] (which is also a common single-word merger in American English, in which the word sure is often /r/); yod-dropping may apply as well, yielding pronunciations such as [p?:] for pure. Other pronunciations in cure-fir merging dialects include /pj?:(r)/ pure, /'k(j)?:ri?s/ curious, /'b(j)?:ro?/ bureau, /'m(j)?:r?l/ mural.
Varieties of Southern American English, Midland American English, and High Tider English may merge words like fire and far or tired and tarred in the direction of the second words: /?r/. This results in a tire-tar merger, but with tower kept distinct.
Some accents of southern British English (including many types of RP, as well as the accent of Norwich) have mergers of the vowels in words like tire, tar, and tower. Thus, the triphthong /a/ of tower merges either with the /a/ of tire (both surfacing as diphthongal ) or with the /?:/ of tar. Some speakers merge all three sounds, so that tower, tire, and tar are all homophonous as [t?:].
The horse-hoarse merger or north-force merger is the merger of the vowels /?:/ and /o?/ (historically /o:/) before historic /r/, making pairs of words like horse-hoarse, for-four, war-wore, or-oar, morning-mourning etc. homophones. This merger occurs in most varieties of English today, despite historically keeping the two phonemes separate. In accents that have the merger, horse and hoarse are both pronounced [h?:(r)s~ho:(r)s], but in accents that do not have the merger hoarse is pronounced with a higher vowel, usually [hors] in rhotic and [ho?s] or the like in non-rhotic accents. Non-merging accents include most Scottish, Caribbean, and older Southern American accents, plus some African American vernacular, modern Southern American, Indian, Irish, and older Maine accents. Some speakers distinguish the vowels by length rather than quality, pronouncing hoarse [hrs] and horse [h?rs].
The distinction was made in traditional Received Pronunciation as represented in the first and second editions of the Oxford English Dictionary. The IPA symbols used are /?:/ for horse and // for hoarse. In the online version of the Oxford English Dictionary, and in the planned third edition (on-line entries), the pronunciations of horse and hoarse are both given as /h?:s/.
In the United States, the merger, though widespread everywhere, is quite recent in some parts of the country. For example, fieldwork performed in the 1930s by Kurath and McDavid shows the contrast robustly present in the speech of Vermont, northern and western New York State, Virginia, central and southern West Virginia, and North Carolina, plus the whole Atlantic coast (North and South), but by the 1990s telephone surveys conducted by Labov, Ash, and Boberg (2006) show these areas as having completely or almost completely undergone the merger; and even in areas where the distinction is still made, the acoustic difference between the  of horse and the [o?] of hoarse is rather small for many speakers. In Labov et al's 2006 study, a majority of white participants in only these American cities continue to resist the merger: Wilmington, North Carolina; Mobile, Alabama; and Portland, Maine. A 2013 study of Portland, however, found the merger already now established in Portland "at all age levels". In Labov et al's study, even St. Louis, Missouri, which traditionally maintained the horse-hoarse distinction so strongly that it instead merged card and cord, showed that only 50% of the participants now continuing to maintain the distinction. The same pattern (a horse-hoarse distinction coupled with a card-cord merger) also exists in a minority of speakers in Texas and Utah. New Orleans prominently shows much variability regarding this merger, including some speakers with no merger at all. Though African Americans are rapidly undergoing the merger, they are also less likely to do so than white Americans, with a little over half of Labov et al.'s black participants maintaining the merger nationwide.
The two groups of words merged by this rule are called the lexical sets north (including horse) and force (including hoarse) by Wells (1982). Etymologically, the north words had /?r/ and the force words had /o?r/.
Spelling-wise, words with the FORCE vowel that are not spelt with an obviously long vowel spelling are relatively more likely to occur in the following circumstances:
|Horse class||Hoarse class|
|aura, aural, border, born, California, corpse, cyborg, fork, form, fortress, forty, horse, important, morgue, morning, morse, morsel, north, porn, spork, tornado, warn||afford, board, borne, Borneo, corps, deport, divorce, export, fjord, force, ford, forge, fort, forth, hoarse, horde, import, mourn, porcelain, porch, pork, port, portal, portend, portent, porter, portion, portrait, proportion, report, shorn, sport, support, sword, sworn, torn, worn|
|boar||boor||'b?:(r)||with cure-force merger|
|Boer||boor||'b?:(r)||with cure-force merger|
|bore||boor||'b?:(r)||with cure-force merger|
The near-square merger or cheer-chair merger is the merger of the Early Modern English sequences /i:r/ and /?:r/ (and the /e:r/ between them), which is found in some accents of modern English. Many speakers in New Zealand merge them in favor of the NEAR vowel, while some speakers in East Anglia and South Carolina merge them in favor of the SQUARE vowel. The merger is widespread in the Anglophone Caribbean, including Jamaican English.
|/(r)/||/e?(r)/||IPA (V=? or e)|
|tear (weep)||tear (rip)||'tV?(r)|
This is the merger of as many as five Middle English vowels /?, ?, ?, ?, ?/ into one vowel when historically followed by /r/ in the coda of a syllable. The merged vowel is /?:/ in Received Pronunciation, and /?r/ in American, Canadian, and Irish English. As a result of this merger, the vowels in words like fir, fur, and fern are the same in almost all modern accents of English; the exceptions are Scottish English and some varieties of Irish English. John C. Wells briefly calls this the NURSE merger. The three separate vowels are retained by some speakers of Scottish English and what has been called the term-nurse merger is resisted by some Irish English speakers, but the full merger is found in almost all other dialects of English.
In local (working-class) Dublin, the West and South-West Region, and other very conservative and traditional varieties of Irish English, ranging from the south to the north of the island, the typical English phoneme /?:r/ actually retains an opposition as two separate phonemes: /?:r/ and /?:r/. For example, the words earn and urn are not pronounced the same in these varieties. In these traditional accents, this NURSE vowel, when after a labial consonant (e.g. fern), when spelled as "ur" or "or" (e.g. word), or when spelled as "ir" after an alveolar stop (e.g. dirt) is pronounced as /?/; in all other situations, this NURSE vowel is pronounced as /?/. Example words with /?/ include certain ['s?:rtn?], chirp [t:rp], circle ['s?:rk?l], earn [?:rn], earth [?:rt], girl [:rl], germ [d:rm], heard or herd [h?:rd], irk [?:rk], and tern [t?:rn]. Example words for /?/ include bird [b?:rd], dirt [d?:rt], first [f?:rst], murder ['m?:rd?], nurse ['n?:rs], turn [t?:rn], third or turd [t?:rd], urn [?:rn], work [w?:rk], and world [w?:rld]. In non-local (middle- and upper-class) Dublin and in younger and supraregional Irish accents, this opposition is seldom preserved, with both of the /?:r/ phonemes typically merged as [?:], the same as, or similar to, most American accents.
In Scottish English, a distinct nurse or fur vowel is also used in:
In Scottish English, a distinct term or fern vowel is used in:
|were||-||whirr||-||'w?:(r)||With wine-whine merger.|
|-||-||whirled||world||'w?:(r)ld||With wine-whine merger.|
Some older varieties of Southern American English and some of England's West Country dialects exhibit a partial merger of nurse-near. These dialects generally realise near as /j?r/, rhyming with nurse (cf. general English realisations of cue and coo), so words such as beard are pronounced as /bj?rd/. Usual word pairs like beer and burr are still distinguished as /bj?r/ vs. /b?r/. However, /j/ drops out after a consonant cluster (e.g. queer) or a palato-alveolar consonant (e.g. cheer), likely due to phonotactic constraints. This results in a merger with nurse in these environments: /kw?r/, /tr/. It is thus possible that pairs like steer-stir are merged in some accents as /st?r/, although this is not explicitly reported in the literature.
There is evidence that African American Vernacular English speakers in Memphis, Tennessee merge both /?r/ and /r/ with /?r/, so that here and hair are both homophonous with the strong pronunciation of her.
The square-nurse merger or fur-fair merger is a merger of /?:(r)/ with /e?(r)/ that occurs in some accents (for example Liverpool, new Dublin, and Belfast). The phonemes are merged to [?:] in Hull and Middlesbrough.
This merger is found in some varieties of African American Vernacular English to the sound IPA: [?r]: "A recent development reported for some AAE (in Memphis, but likely found elsewhere)". This is exemplified in Chingy's song "Right Thurr"; the merger is heard at the beginning of the song, but he goes on to use standard pronunciation for the rest of the song.
Labov (1994) also reports such a merger in some western parts of the United States "with a high degree of r constriction".
|share||sure||':(r)||with cure-fir merger|
|ware||whir||'w?:(r)||with wine-whine merger|
|wear||whir||'w?:(r)||with wine-whine merger|
|where||were||'w?:(r)||with wine-whine merger|