Phonemic differentiation is the phenomenon of a phoneme in a language splitting into two phonemes over time, a process known as a phonemic split. The opposite of a phonemic split is a phonemic merger, in which two phonemes become one over time.

These splits and mergers may be complete, or limited to certain phonemic contexts. In the former case, all minimal pairs for the two phonemes in a splitting accent will be homonyms in a merging accent; in the latter case, only some pairs will be homonyms. For example, the cot-caught merger completely merges and /ɔ/, whereas the horse-hoarse merger merges /ɔː/ and /oʊ/(/ə&#650/]) only before a lexical r (for example bought and boat remain distinct).

It is sometimes difficult to determine whether a split or a merger has happened in cases where one dialect has two phonemes corresponding to a single phoneme in another dialect; diachronic research is usually required to determine which dialect is the conservative and which is the innovative. It is also important to note that while some splits and mergers are considered to be part of standard languages, others are not considered standard and may be stigmatized. In descriptive linguistics, however, the question of which splits and mergers are prestigious and which are stigmatized is irrelevant.

Occasionally, speakers of one accent may believe the speakers of another accent to have undergone a merger, when in fact there has been a chain shift. For example, an American may hear an Irish person use pronunciations like [bɑɹn] for born, [fɑɹm] for form, and [kɑɹd] for cord and incorrectly conclude that Hiberno-English has undergone the Start-north merger. In fact, there is no merger in Hiberno-English: the words barn, farm, and card are pronounced [bæɹn, fæɹm, kæɹd].

Phonemic differentiation in English

The various accents of English are characterized by various splits and mergers. Listed below are cases where a single phoneme of Early Modern English has split in two or more accents of Modern English, and cases where two phoneme of Middle English have merged in two or more accents of Modern English. Splits and mergers that affect only one accent (or have failed to affect only one accent) are discussed in the article on the accent in question (see the list of English accents and dialects at the right). Many (but not all) of the names used in this section were coined by John C. Wells in his book Accents of English (Cambridge University Press, 1982).

Bad-lad split

The bad-lad split is a phonemic split of the Early Modern English short vowel phoneme /æ/ into a short /æ/ and a long /æː/. This split is found in some varieties of English English and Australian English in which bad (with long [æː]) and lad (with short [æ]) do not rhyme.

A very similar split, apparently historically independent, is the æ-tensing found in several northeastern accents of American English. In some of these accents, can (the metal container) is pronounced [keən] and can (able to) is pronounced [kæn]; likewise bad may be [beəd] as opposed to lad [læd].

Cot-caught merger

Main article: cot-caught merger

Father-bother merger

The father-bother merger is a merger of the Early Modern English vowels /ɑ/ and /ɒ/ that occurs in almost all varieties of North American English (except the Boston accent) and also occurs in Hiberno-English. In those accents with the merger father and bother rhyme, and balm and bomb are homophonous as [bɑm].

Fleece merger

The fleece merger is the merger of the Early Modern English vowel /eː/ (usually spelled ea, as in meat, peace, sea, receive) with the vowel /iː/ (as in meet, piece, see, believe). The merger is complete outside the British Isles and virtually complete within them. Some speakers in Northern England distinguish [ɪə] in the first group of words from [iː] or [əi] in the second group. Old-fashioned varieties of Hiberno-English and the West Country accent preserve the Early Modern English /eː/–/iː/ contrast, but it rare in these accents nowadays. A handful of words (such as break, steak, great) escaped the fleece merger in the standard accents and are thus have the same vowel as words like brake, stake, grate in almost all varieties of English.

Glide cluster reduction

Glide cluster reduction, or the which-witch merger, is a merger by which the sound /ʍ/ or sequence /hw/ (spelled wh) becomes [w]; it occurs in the speech of the great majority of English speakers. The merger is essentially complete in England, Wales, the West Indies, Australia, New Zealand, and South Africa, and is widespread in the United States and Canada. In accents with the merger, pairs like wine/whine, wet/whet, weather/whether, Wales/whales, wear/where etc. are homophonous. The merger is not found in Scotland, Ireland, and parts of the U.S. and Canada. The merger is not usually stigmatized except occasionally by very speech-conscious people, who sometimes make hypercorrections. The actor Michael Dorn, for instance, playing a Klingon security officer on Star Trek: The Next Generation, frequently pronounced weapons /ʍɛpənz/.

According to the Telsur project of William Labov and others, while there are regions of the U.S. (particularly in the South and the Midwest) where speakers keeping the distinction are about as numerous as those having the merger, there are no regions where the preservation of the distinction is predominant (see map). Nationwide, about 88% of respondents in the survey had the merger, while about 11% preserved the distinction.

Glide cluster reduction can also refer to the simplification of [hj] to [j], leading to pronunciations like /juːdʒ/ for huge and /juːmən/ for human; hew and yew become homophonous. This process is much less widespread than wh-reduction, and is generally stigmatized where it is found.

Horse-hoarse merger

The horse-hoarse merger is the merger of the vowels /ɔː/ and /oʊ/ before 'r', making pairs of words like horse/hoarse, for/four, war/wore, or/oar, corps/core, morning/mourning etc. homophones. This merger occurs in almost all varieties of English. In accents that have the merger horse and hoarse are both pronounced [hɔː(ɹ)s], but in accents that don't have the merger (notably Scottish English, also to some extent in Hiberno-English, the Boston accent, and Southern American English) hoarse is pronounced with the o sound in home ([hoɹs]).

Long mid mergers

The earliest stage of Early Modern English had a contrast between the long mid monophthongs /ɛː, oː/ (as in pane, toe) and the diphthongs /ɛi, ɔu/ (as in pain, tow). In the vast majority of Modern English accents these have been merged; whether the outcome is monophthongal or diphthongal depends on the accent. But in a few regional accents, including some in Northern England, East Anglia, South Wales, and even Newfoundland, the merger has not gone through (at least not completely), so that pairs like pane/pain and toe/tow are distinct.

Lot-cloth split

The lot-cloth split is the result of a late seventeenth-century sound change that lengthened /ɒ/ to [ɒː] before voiceless fricatives. In some accents, the lengthened [ɒː] was raised, merging with the /ɔː/ of words like thought. Words that entered the language later, or words that were used more in writing than speech, were often exempt from the lengthening, so that joss and Goth still have the short vowel.

As a result of the lengthening and raising, in the above-mentioned accents cross rhymes with sauce, and soft and cloth also have the vowel [ɔː]. Accents affected by this change include American English and, originally, RP, although today words of this group almost always have short [ɒ] in RP.

In American English the raising was extended to the environment before [ŋ] and in a few words to the environment before [k, g] as well, giving pronunciations like /lɔŋ/ for long, /tʃɔklət/ for chocolate, and /dɔg/ for dog. Obviously, in accents of American English that are subject to the cot-caught merger, there is no difference between words that did and those that did not undergo the change.

Near-square merger

The near-square merger is the merger of the Early Middle English sequences [iːr] and [eːr], which is found in some accents of modern English. Some speakers in New York City and 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.

NG coalescence

NG coalescence is the name given to a sound change by which word-final [g] was deleted after [ŋ]; this sound change happened around the end of the 16th century. As a result of NG coalescence, Middle English /sɪŋg/ sing came to be pronounced [sɪŋ]. NG coalescence was applied also in cases where a verb ending in -ng was followed by a vowel-initial suffix, so singing and singer also underwent the change. Otherwise, word-internal -ng- did not undergo coalescence and the pronunciation [-ŋg-] was retained, as in finger, angle. (In adjectives ending in -ng the [-ŋg-] is retained when the comparative and superlative suffixes are added, so younger, strongest, etc., do not show coalescence.) As a result of the asymmetric application of this merger word-internally, the words finger and singer do not rhyme in most accents of English, although they did in Middle English.

In some accents, however, they do rhyme. In places like Birmingham, Manchester, Liverpool, and New York City, NG coalescence is not found, so that sing and singer are pronounced with [ŋg]. In some accents of the west of Scotland and Ulster, NG coalescence is extended to word-internal position, so that finger is pronounced /fɪŋər/.

Nurse mergers

The nurse mergers are two different sound changes in the history of English by which formerly distinct sequences of short vowel + [r] merged into [ɜr].

The first nurse merger is the merger of the Middle English vowels /ɪ, ɛ, ʊ/ into [ɜ] when followed by [r] in the coda of the syllable. As a result of this merger, the vowels in fern, fir and fur are the same in almost all accents of English; the exceptions are Scottish English and some accents of the north and south of Ireland. The vowel quality is preserved when vowel-initial suffixes are added to words that came to end in [ɜr] by this merger, so furry has the same vowel as fur and stirring has the same vowel as stir. Otherwise the merger did not happen when the [r] sound was intervocalic, so that mirror, very, and furrow still have distinct vowels.

The second nurse merger is a form of tense-lax neutralization (see below) found in most varieties of North American English outside the Northeast and coastal South. This merges the vowel of words like furrow (in which the first nurse merger did not apply, because the [r] is intervocalic) with the vowel of words like fur and furry (in which the first nurse merger did apply). In accents with the merger, hurry /hɜri/ rhymes with furry /fɜri/. In accents without the merger, they are distinct as /hʌri/ vs. /fɜri/.

Nurse-square merger

The nurse-square merger is a merger of /ɜː(r)/ with /ɛə(r)/ that occurs in some accents (for example Liverpool, Dublin, and Belfast) that makes homophonous pairs such as fur/fair, spur/spare, and curd/cared.

Pin-pen merger

The pin-pen merger is a conditional merger of /ɪ/ and /ɛ/ before the nasal consonants [m], [n], and [ŋ]. The merged vowel is usually closer to [ɪ] than to [ɛ]. The merger is widespread in the Southern United States, and is also found in many speakers in the "Midland" region immediately north of the South, as well as in less densely populated inland areas of the Western United States. See map.

Pour-poor merger

The pour-poor merger is a merger of the vowels /ɔː/ and /uː/ before 'r' that occurs for many English speakers. In these accents pour and poor are both pronounced [pɔː(ɹ)], moor and more are both pronounced [mɔː(ɹ)], tour and tore are both pronounced [tɔː(ɹ)]. In the United States this merger is characteristic of Southern American English, African American Vernacular English, and accents of the Northeast (northeastern New England, New York, and Philadelphia). In England, the merger is widespread among all social classes and is found even among younger RP speakers.

Start-north merger

The start-north merger is a merger of Early Modern English [ɑr] with [ɒr], resulting in homophony of pairs like card/cord, barn/born and far/for. The merger is found in some Caribbean English accents, in some versions of the West Country accent in England, and in some Southern and Western U.S. accents.

Tense-lax neutralization

Tense-lax neutralizations are a feature of many North American English accents, by which the historical "short" vowel classes merge with the nearest "long" vowel before intervocalic r. Two of the best-known tense-lax neutralizations are known collectively as the Mary-marry-merry merger, which consists of the mergers before intervocalic r of the "short a" and "short e" classes with the historical "long a" class.

Other widespread tense-lax neutralizations include merger of "short i" with "long e" (mirror-nearer), "short u" with syllabic r (hurry-furry), and "short o" with "long o" (torrent-tory). In the Philadelphia accent, "short e" is neutralized not with "long a" but with syllabic r, so ferry sounds not like fairy but like furry.

Frequently, though not always, the result of tense-lax neutralization is a vowel that is identical to the corresponding long vowel before syllable-final r. For instance, in dialects where merry and Mary are merged, they typically both have the same vowel as mare; in dialects where mirror and nearer rhyme, they generally have the same vowel as near.

Not all dialects that have tense-lax neutralization in one vowel class have it in all classes. The aforementioned Philadelphia accent, for example, has tense-lax neutralization for "short e" and "short u" (both neutralized with syllabic r), but maintains "short a" as in carry as a distinct unmerged class before r. Among United States accents, the Boston and New York accents have the least degree of tense-lax neutralization. Some research suggests that, in general, rhotic accents are more likely to have tense-lax neutralization than non-rhotic accents.

TH fronting

TH fronting is a merger that occurs (historically independently) in Cockney, Newfoundland English, and African American Vernacular English (though the details differ among those accents), by which Early Modern English [θ, ð] merge with [f, v].

Apparently, no accents with the merger completely merge the phonemes, because virtually all speakers of such accents know which words "should" have which sound; moreover, in many accents the two sounds appear in free variation. Where TH fronting is applied, pairs such as three/free, slither/sliver, and oath/oaf are homophonous.

Trap-bath split

The trap-bath split is a vowel split that occurs mainly in southern varieties of English English, in the Boston accent, and in the Southern Hemisphere accents (Australian English, New Zealand English, South African English), by which the Early Modern English phoneme /æ/ was lengthened in certain environments and ultimately merged with the long /ɑː/ of father. Accents that have undergone this split are said to have a broad A in as set of words that typically includes after, chance, branch, example, rather, bath, pass, fast, can't, past, half, calf, answer, etc.

Weak vowel merger

The weak vowel merger is a merger of schwa with unstressed /ɪ/ (sometimes written as /ɨ/). As a result of this merger the words affect and effect are homophonous, in accents without the merger they are distinct. The merger is complete in the Southern Hemisphere accents and variable in General American and Hiberno-English.

See also

• List of dialects of the English language
• British English
• American and British English differences
• Scots Vowel Length Rule

Phonemic differentiation in Spanish

Two well-known mergers in Spanish are [ʎ]/[j] and [θ]/[s]. In many accents of Spain and most accents of Latin America, these two pairs have merged in favor of [j] and [s], respectively. As a result, pairs like cayo/callo, maya/malla, vaya/valla, and casa/caza have become homophonous.

Phonemic differentiation in German

The Middle High German vowel pairs [ei]/[iː] and [ou]/[uː] have merged to [ai] and [au] respectively in modern standard German, but not in many dialects. For example, while zwei 'two' (MHG zwei) and drei 'three' (MHG drî) rhyme in the standard language, they do not in the dialects spoken in Bavaria (zwoa/dräi) and Berlin (zwee/drei), nor in Yiddish (tsvey/dray), also a descendant of Middle High German.

Another merger found in many accents of German is that of /ɛː/ (spelled ä(h)) with /eː/ (spelled e, ee, or eh). Some speakers merge the two everywhere, some distinguish them everywhere, others keep /ɛː/ distinct only in conditional forms of strong verbs (for example they distinguish ich gäbe 'I would give' vs. ich gebe 'I give', but not Bären 'bears' vs. Beeren 'berries').

See also

• H-dropping
• Yod-dropping