The – split is a vowel split that occurs mainly in Southern England English (including Received Pronunciation), Australian English, New Zealand English, Indian English, South African English and to a lesser extent in some Welsh English as well as older Northeastern New England English by which the Early Modern English phoneme pronounced as //æ// was lengthened in certain environments and ultimately merged with the long pronounced as //ɑː// of . In that context, the lengthened vowel in words such as bath, laugh, grass and chance in accents affected by the split is referred to as a broad A (also called in Britain long A). Phonetically, the vowel is pronounced as /link/ in Received Pronunciation (RP), Cockney and Estuary English; in some other accents, including Australian and New Zealand accents, it is a more fronted vowel (pronounced as /link/ or pronounced as /link/) and tends to be a rounded and shortened pronounced as /[ɒ~ɔ]/ in Broad South African English. A trap–bath split also occurs in the accents of the Middle Atlantic United States (New York City, Baltimore, and Philadelphia accents), but it results in very different vowel qualities to the aforementioned British-type split. To avoid confusion, the Middle Atlantic American split is usually referred to in American linguistics as a 'short-a split'.
In accents unaffected by the split, words like bath and laugh usually have the same vowel as words like cat, trap and man: the short A or flat A. Similar changes took place in words with (o) in the lot–cloth split.
The sound change originally occurred in Southern England and ultimately changed the sound of pronounced as /link/ to pronounced as /link/ in some words in which the former sound appeared before pronounced as //f, s, θ, ns, nt, ntʃ, mpəl//. That led to RP pronounced as //pɑːθ// for path, pronounced as //tʃɑːnt// for chant etc. The sound change did not occur before other consonants and so accents affected by the split preserve pronounced as //æ// in words like cat. (See the section below for more details on the words affected.) The lengthening of the bath vowel began in the 17th century but was "stigmatised as a Cockneyism until well into the 19th century".[1] However, since the late 19th century, it has been embraced as a feature of upper-class Received Pronunciation.
The presence or absence of this split is one of the most noticeable differences between different accents of England. An isogloss runs across the Midlands from the Wash to the Welsh border, passing to the south of the cities of Birmingham and Leicester. North of the isogloss, the vowel in most of the affected words is usually the same short-a as in cat; south of the isogloss, the vowel in the affected words is generally long.[2]
There is some variation close to the isogloss; for example in the dialect of Birmingham (the so-called 'Brummie') most of the affected words have a short-a, but aunt and laugh usually have long vowels. Additionally, some words which have pronounced as //æ// in most forms of American English, including half, calf, rather, can't and shan't, are usually found with long vowels in the Midlands and Northern England. The split is also variable in Welsh English, often correlated with social status. In some varieties, such as Cardiff English, words like ask, bath, laugh, master and rather are usually pronounced with pronounced as //ɑː// while words like answer, castle, dance and nasty are normally pronounced with pronounced as //æ//. On the other hand, the split may be completely absent in other varieties like Abercraf English.
In northern English dialects, the short A is phonetically pronounced as /[a~a̠]/, while the broad A varies from pronounced as /[ɑː]/ to pronounced as /[aː]/; for some speakers, the two vowels may be identical in quality, differing only in length (pronounced as /[a]/ vs pronounced as /[aː]/). John Wells has claimed that Northerners who have high social status may have a trap–bath split and has posted on his blog that he grew up with the split in Upholland, Lancashire.[3] AF Gupta's study of students at the University of Leeds found that (on splitting the country in two halves) 93% of northerners used pronounced as /[a]/ in the word bath and 96% of southerners used pronounced as /[ɑː]/. However, there are areas of the Midlands where the two variants co-exist and, once these are excluded, there were very few individuals in the north who had a trap–bath split (or in the south who did not have the split). Gupta writes, 'There is no justification for the claims by Wells and Mugglestone that this is a sociolinguistic variable in the north, though it is a sociolinguistic variable on the areas on the border [the isogloss between north and south]'.
In some West Country accents of English English in which the vowel in trap is realised as pronounced as /[a]/ rather than pronounced as /[æ]/, the vowel in the bath words was lengthened to pronounced as /[aː]/ and did not merge with the pronounced as //ɑː// of father. In those accents, trap, bath, and father all have distinct vowels pronounced as //a//, pronounced as //aː//, and pronounced as //ɑː//.
In Cornwall, Bristol and its nearby towns, and many forms of Scottish English, there is no distinction corresponding to the RP distinction between pronounced as //æ// and pronounced as //ɑː//.
In Multicultural London English, pronounced as //θ// sometimes merges with pronounced as //t// but the preceding vowel remains unchanged. That leads to the homophony between bath and path on the one hand and Bart and part on the other. Both pairs are thus pronounced pronounced as /[ˈbɑːt]/ and pronounced as /[ˈpɑːt]/, respectively, which is not common in other non-rhotic accents of English that differentiate pronounced as //ɑː// from pronounced as //æ//. That is not categorical, and th-fronting may occur instead and so bath and path can be pronounced as /[ˈbɑːf]/ and pronounced as /[ˈpɑːf]/ instead, as in Cockney.
In Received Pronunciation (RP), the trap–bath split did not happen in all eligible words. It is hard to find a clear rule for the ones that changed. Roughly, the more common a word, the more likely that its vowel changed from flat pronounced as //æ// to broad pronounced as //ɑː//. It also looks as if monosyllables were more likely to change than polysyllables. The change very rarely took place in open syllables except if they were closely derived from another word with pronounced as //ɑː//. Thus, for example, passing is closely derived from pass and so has broad A pronounced as //ˈpɑːsɪŋ//, while passage is not so closely derived and so has flat A pronounced as //ˈpæsɪd͡ʒ//. Here is the set of words that underwent transition and counterexamples with the same environment: