I was wondering why we pronounce the vowels in the words south and southern. They seem to be very closely related to each other. Both refer to the same direction. South is a noun and Southern is an adjective, which I don't think caused them to have a different vowel.

Oxford Dictionary shows that south is /saʊθ/ and southern is /ˈsʌð(ə)n/. In short, south has a long vowel and southern has short.

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    Also see Christ Vs Christmas – Void Nov 9 '20 at 19:32
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    Just echoing @Void’s recommendation, as the “Christ vs Christmas” answer is one of the best on Stack Exchange. – KRyan Nov 10 '20 at 3:19
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    It would be the same had there been any justice in this world. – Aravind Suresh Nov 10 '20 at 11:54
  • If you try to properly pronounce southern the way you are wondering why it is not pronounced (probably /saʊðən/ or, in America, /saʊðərn/), you may get an idea for the reason. – Peter - Reinstate Monica Nov 10 '20 at 16:24
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    Also think of "pronounce" vs. "pronunciation". In their case, the spelling changes too (pronoun... -> pronun...), but the second vowel sound has the same change as with "south" and "southern". – Panzercrisis Nov 11 '20 at 3:56


The reason why the vowels in the first syllables of 'south' and 'southern' are different is Trisyllabic Laxing (TSL) which was a phonological rule back in Old and Middle English. It's a process whereby a long vowel/diphthong is shortened if two or more syllables follow.

'Southern' was a three-syllable word when TSL applied to it. TSL shortened the vowel in its first syllable, therefore it has a short vowel even in Modern English. There are some other pairs showing the same distinction such as derive-derivative, divine-divinity, pronounce-pronunciation, serene-serenity, impede-impediment, insane-insanity, profane-profanity etc.


Trisyllabic Laxing

It's a process whereby a tense vowel (long vowel or a diphthong) is laxed (shortened) if two (or more) syllables follow.
As we add syllables to the base of a word in English, we tend to reduce the length of the vowel in the base. If a syllable having tense vowel is followed by two or more syllables, the tense vowel often becomes lax.

At one point, this rule applied to all relevant cases; it was therefore purely a phonological rule, a constraint upon what was pronounceable in English. Later on, it ceased to be a part of English phonology, however, its remnants are still highly visible in Modern English.


  • insane /ɪnˈsn/ → insanity /ɪnˈsæn.ə.ti/
  • sincere /sɪnˈsɪə/ → sincerity /sɪnˈsɛ.rə.ti/
  • serene /səˈrn/ → serenity /səˈrɛ.nə.ti/
  • divine /dɪˈvn/ → divinity /dɪˈvɪ.nə.ti/
  • pronounce /prəˈnns/ → pronunciation /prəˌnʌn.siˈeɪ.ʃ(ə)n/
  • provoke /prəˈvəʊk/ → provocative /prəˈvɒk.ə.tɪv/

Another interesting example is holy - holiday.

  • Holy /ˈhəʊli/ → holiday /ˈhɒlɪdeɪ/

As you can see, there are at least two syllables after the tense vowels, so they get laxed because of TSL.

There's a fairly regular pattern of the vowel change in the words I mentioned above. It can be summarised as:

  • /eɪ/ → /æ/
  • /ɪə/ → /ɛ/
  • /iː/ → /ɛ/
  • /aɪ/ → /ɪ/
  • /aʊ/ → /ʌ/
  • /əʊ/ → /ɒ/ (AmE: /ɑ/)


In Modern English, there are systematic exceptions to the process, such as in words ending in -ness (e.g. mindfulness, loneliness etc). There are also occasional, non-systematic exceptions including later borrowings such as obese-obesity.

  • Obese /əʊˈbs/ → obesity /əʊˈb.sə.ti/ not /əʊˈbɛ.sə.ti/
  • Nightingale /ˈn.tɪŋ.ɡeɪl/
  • Some words having the suffix -able such as signable /snəb(ə)l/, boatable /ˈbəʊtəb(ə)l/ etc.

There are lots of other exceptions, however.

The above changes happen in trisyllabic (three-syllable) or polysyllabic words, but 'southern' is not even a three-syllable word, why then is it pronounced with a short vowel?

The short vowel in 'southern'

The history of southern is more interesting. Wikipedia also mentions disyllabic laxing (when one syllable follows the tense vowel as in 'southern'), though the vowel in 'southern' is not the result of that. It is because of trisyllabic laxing.

How come Trisyllabic laxing caused 'southern' to have a short vowel instead of a long vowel?

The anomaly here is caused by historical sound changes. 'Southern' used to be a three-syllable word when Trisyllabic Laxing applied.

'South' was sūþ (or sūð)1 in Old English and it was pronounced /suːθ/. While 'southern' was sūþerne2 (or sūðerne) pronounced /ˈsuː.θer.ne/ ([ˈsuː.ðer.ne])

In Middle English, 'southern' was pronounced /ˈsuː.ðər.nə/. Then Trisyllabic Laxing applied to it and reduced the long vowel /uː/ to /ʊ/ (the vowel in put).

Then in Early Modern English, there was another sound change that caused the unrounding of the round vowel /ʊ/ in most varieties of English (exceptions being most accents of Northern England3 and Midlands) and changed it to /ʌ/ (vowel in strut). So the round vowel of 'southern' changed to /ʌ/.

'South' was pronounced /suːθ/ until the Great Vowel Shift, which changed the /uː/ vowel to /aʊ/ (vowel in mouth).


  1. Both ⟨þ⟩ (þornthorn) and ⟨ð⟩ (eth) were used interchangeably to represent the th sounds in Old English. And ⟨ū⟩ represented the long U sound // (as in moon).
  2. The final e was pronounced up until late Middle English.
  3. That's why most northerners rhyme but with put.


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    @Mxtt: A diphthong is a combination of two different vowels. Like the EYE sound in 'right'; you glide from /a/ to /ɪ/. That's a diphthong. – Void Nov 9 '20 at 10:43
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    Like many English rules, TSL also has lots and lots of exceptions, however. – Void Nov 9 '20 at 14:12
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    Absolutely incredible answer. Would give more reputation if I knew how, but there doesn't seem to be a way to start a bounty. – DRF Nov 10 '20 at 18:57
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    @DRF: I'm glad you enjoyed it. (Very pleased to hear that! Words are enough! :) – Void Nov 10 '20 at 19:06
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    @RockPaperLz-MaskitorCasket: 'southern' was sūþerne and it was pronounced [ˈsuː.ðer.ne] (three syllables). In Middle English, the ending -e was pronounced [ə] and then lost. – Void Feb 15 at 15:39

Void has an amazing and thorough answer. I would add one further point, which is that the weird patterns of the laxing make a whole lot more sense if recognize that it occurred in English before the Great Vowel Shift, which kept the short vowels sort of similar, and the utterly messed up the long vowels. In Old and Middle English, a "long vowel" was literally that, a vowel that was held longer. So the letter "e" was pronounced like "/e/" regardless of whether it was long (/e:/) or short (/e/), excepting that it was different in length.

However, after the GVS, the long /e:/ sound shifted to /i:/ (now the name of the letter). So words like serene and serenity would have been closer to /se're:n/ and /se're ni ti/. However, when the long /e:/ shifted, you ended up with /se'ri:n/ and /se're ni ti/, plus some other shifting.

Basically in summary, the "shortening" was due to slightly less emphasis placed on a vowel after two more syllables were added to it. And then the GVS came along and really messed up the pronunciation of the long version, making the sounds seem way more different than they originally were.

Coda: A similar phenomenon happened with the pair wind/windmill (currently /wɪnd/ and /'wɪnd mɪl/), with an extra twist. In Middle English, the pair was /wind/ and /'wind mill/. With the GVS, the first one became /waind/ (the same sound you get for "wind a watch"). So you had the slightly odd pair /waind/ and /wɪnd mɪl/. And English speakers sort of unanimously rejected that pairing some point in the later 18th century, since the words were so different.

But its legacy can be found in Shakespeare (As you like it), where the rhyme goes along with "kind":

"Blow, blow, thou winter wind (/waind/), Thou art not so unkind (/kaind/)"


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