In Southern standard British English, bath is pronounced as /bɑːθ/ with a long a while maths is pronounced as /mæθs/ with a short ae sound. Why does that happen?

Both maths and bath end with θ. Even though both of them start with bilabial sounds they are pronounced differently. Is there any rule for that?

  • Even in AE the sound changes when you add the S. – Hot Licks Apr 30 '20 at 12:26
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    No rule that I know of as a southern BrE speaker. Don't forget though, that maths is an abbreviation of mathematics. – Weather Vane Apr 30 '20 at 12:28
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    Also the word hath (still used in sayings) is pronounced with a short a sound, but aftermath with a long a. – Weather Vane Apr 30 '20 at 12:32
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    @WeatherVane - You're kidding, eh? – Hot Licks Apr 30 '20 at 13:00
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    @HotLicks, I speak the way I speak, just as you do. Please don't pull the "where the heck did you learn English anyway" thing on me, because I learned it in England. – Weather Vane Apr 30 '20 at 13:46

The pronunciation of ath as /ɑːθ/ in certain British accents applies mainly to monosyllabic words. (There's also /ɑːðə(r)/ in the disyllables lather, rather.) Polysyllabic words like pathogen, Catherine, cathode have /æ/. Although maths is one syllable, it is short for the polysyllabic word mathematics /ˌmæθəˈmætɪks/, and so is pronounced with the same vowel sound in the first syllable.

Similarly, according to the Oxford English Dictionary, staph which is short for staphylococcus is pronounced only as /stæf/, unlike staff which can be pronounced as /stɑːf/.

So I would say the general rule is that /æ/ does not change to /ɑː/ in words that are short forms of longer words with /æ/. There is at least one word that could be considered an exception: graph, which the OED says was "Originally an abbreviation of graphic formula", and which can be pronounced as /grɑːf/. But I think that in modern times, people don't think of graph as short for anything, so I would argue that it is not a genuine exception.


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