The trap-bath split (also TRAP-BATH split) is a vowel split that occurs mainly in southern accents of English in England (including Received Pronunciation), in New Zealand English, Indian English and South African English, and also to a lesser extent in Australian English as well as older Northeastern New England English (notably, older Boston accents), by which the Early Modern English phoneme /æ/ was lengthened in certain environments and ultimately merged with the long /?:/ of father. In this context, the lengthened vowel in words such as bath, laugh, grass, chance in accents affected by the split is referred to as a broad A (also, in the UK, long A). Phonetically, the vowel is in Received Pronunciation (RP); in some other accents, including Australian and New Zealand accents, it is a fronter vowel ( or ), and it tends to be a rounded and shortened [?~?] in Broad South African English. A TRAP-BATH split also occurs in the accents of the Middle Atlantic United States (New York, Baltimore, and Philadelphia accents), but it results in very different vowel qualities to the aforementioned British-type split and so, to avoid confusion, is usually referred to in American linguistics as a 'short-a split'.
In accents unaffected by the split, words like bath, laugh, etc. usually have the same vowel as words like cat, trap, man: the short A or flat A. Similar changes took place in words with ⟨o⟩; see lot-cloth split.
The sound change originally occurred in southern England, and ultimately changed the sound of to in some words in which the former sound appeared before /f, s, ?, ns, nt, nt?, mp?l/, leading to RP /p?:?/ for path and /'s?:mp?l/ for sample, etc. The sound change did not occur before other consonants; thus accents affected by the split preserve /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";:122 since the late 19th century onward, 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 English English. 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.
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 /æ/ in most forms of American English, including half, calf, rather, and can't, are usually found with long vowels in the Midlands and Northern England.
In northern English dialects, the short A is phonetically [a ~ a?], while the broad A varies from [?:] to [a:]; for some speakers, the two vowels may be identical in quality, differing only in length ([a] vs [a:]).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. AF Gupta's study of students at the University of Leeds found that (on splitting the country in two halves) 93% of northerners used [a] in the word 'bath' and 96% of southerners used [?:]. 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 where the vowel in trap is realised as [a] rather than [æ], the vowel in the bath words was lengthened to [a:] and did not merge with the /?:/ of father. In those accents, trap, bath, and father all have distinct vowels /a/, /a:/, and /?:/..[further explanation needed]
In Cornwall, Bristol (as well as towns around Bristol), and in many forms of Scottish English, there is no distinction corresponding to the RP distinction between /æ/ and /?:/.
In Multicultural London English /?/ sometimes merges with /t/, but the preceding vowel remains unchanged. This leads to the homophony between bath and path on one hand and Bart and part on the other (with both pairs being pronounced ['b?:t] and ['p?:t], respectively), which is not common in other non-rhotic accents of English. This is not categorical and th-fronting may occur instead, so that bath and path can be ['b?:f] and ['p?:f] 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 the change from flat /æ/ to broad /?:/ took place. It also looks as if monosyllables were more likely to change than polysyllables. The change very rarely took place in open syllables, except where closely derived from another word with /?:/. Thus passing is closely derived from pass, and so has broad A /p?:s/: passage is not so closely derived, and thus has flat A /pæs?d?/. Here is the set of words that underwent transition, and counterexamples with the same environment:
|RP sets for the trap-bath split|
For the words in the last row, subsequent sound changes have altered the conditions initially responsible for lengthening
There are some words in which both pronunciations are heard among southern speakers:
Use of broad A in mass is distinctly conservative and rare now: other international fluctuations are both common, but with further complications.
While graph, telegraph, photograph can have either (now in Received Pronunciation, they have broad A), graphic and permutations always have a flat A.
Broad A fluctuates in dialects that include it; before s it is a more common alternative when in its common voiceless variant (/s/ rather than /z/) (in transfer [t:nsf?:], transport [t:nsp?:t] and variants) than when it is voiced (thus translate [t?ænzle?t], trans-Atlantic [t?ænz?tlænt?k]).
Some research has concluded that many people in the North of England have a dislike of the /?:/ vowel in BATH words. AF Gupta writes, 'Many of the northerners were noticeably hostile to /?r?:s/, describing it as "comical", "snobbish", "pompous" or even "for morons".' Whilst writing on a Labovian study of speech in West Yorkshire, K. M. Petyt wrote in 1985 that several respondents 'positively said that they did not prefer the long-vowel form or that they really detested it or even that it was incorrect'. However, Joan Beal said in a 1989 review of Petyt's work that those who disliked the pronunciation still associated it with the BBC and with the sort of professional jobs that they would aspire to.
Evidence for the date of the shift comes from the Southern Hemisphere accents, those of Australia, New Zealand, and South Africa.
In Australian English, there is generally agreement with southern British in words like path, laugh, class. However, with the exception of South Australian English, before /n/ or /m/, such as dance, plant, example, most Australians use a flat A; the words aunt, can't, shan't, are invariably pronounced with a broad A. Phonetically, the broad A is [ä:]. In Australia there is variation in the word castle, both pronunciations are commonly heard. For more information, see the table at Variation in Australian English. In South Australian English the broad A is usually used.
South African and New Zealand English have a distribution of sounds similar to that of RP.
Most accents of American English and Canadian English are unaffected by the split. The main exceptions are parts of New England (see Boston accent) and in the Plantation South, where the broad sound can be used in some of the same words as in southern England, such as aunt, ask, bath etc. ('Aunt', though, is unique, as the broad-a pronunciation is found sporadically throughout the US, not only in New England.) By the early 1980s, the broad /a/ was in decline in New England.
Related, but distinct, phenomena include the following: