Vowel breaking is a sound change whereby a single vowel changes to become a diphthong in specific environments. The resulting sound preserves the original vowel, which is either preceded or followed by a glide. This process is manifested in a variety of Germanic languages and is characteristic of Old English.
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In historical linguistics vowel breaking is defined as an assimilatory sound change that implies the diphthongization of single vowels due to the influence of a neighboring sound. The first segment of the resulting diphthong coincides with the original vowel whereas the second is a glide the articulatory characteristics of which are determined by the triggering sound. This process is well attested in Old English where certain front vowels, /æ/ /e/ and /i/, in their short and long variants, were diphthongized when immediately followed by a velar /x/ or a cluster containing a velarized consonant and /ł/ or /r/, as its first element.
/æ/ > /æu/ / ___ /x/ /æ/ > /æu/ / ___ /ł/ or /r + C
/e/ > /eu/ / ___ /x/ /e/ > /eu/ / ___ /ł/ or /r + C
/i/ > /iu/ / ___ /x/ /i/ > /iu/ / ___ /ł/ or /r + C
In this context, the glide appeared as a transition sound in response to the tongue movements performed when articulating the vowels at the front of the mouth and the consonants at the back of the mouth. The result was the production of a diphthong the second segment of whichanticipated the consonant that was about to come.In a subsequent step, according to Lass, the previous diphthongs underwent a process of height harmony which turns the inserted glide into a schwa-like vowel.
(1) Gmc *werpan > OE weorpan /wĕŏrpɑn/ "to throw"
(2) Gmc.*elh > OE eolh/ĕŏɫx/ "elk"
(3) Gmc *hælp > OE healp/hæ̆ăɫp/ "helped”
From a wider perspective, the term breaking (as a calque from Grimm, 1822, Brechung) is also applied to a wide variety of vowel shifts that do not necessarily imply a process of diphthongization but only the alteration of a vowel due the influence of another sound. That is the case of Gothic /i/ and /u/, which in contact with /r/ and /h/ were spelt as ‘iu’ and ‘au’ respectively, but pronounced as single mid-open vowels, /ɛ/ and /ɔ/.
(4) Gothic taihun/tɛhun/ "ten"
(5) Gothic dauhtar /dɔxtar/ “daughter”
Related concepts
Conditioned sound change
Assimilation
Basic bibliography
Algeo, J. - Pyles, T. (2004), The Origins and Development of the English Language 5th, Wadsworth Publishing.
Brinton, L. - Arnovick, L. (2006), The English Language: A Linguistic History, Oxford, University Press.
Campbell, L. (2nd ed) (2004), Historical Linguistics: An Introduction, Edinburgh,Edinburgh University Press.
Campbell, L. - Mixco, M. (2007 ), Glossary of Historical Linguistics, Edinburgh, Edinburgh University Press.
Lass, R. (1994), Old English. A Historical Linguistic Companion, Cambridge, Cambridge University Press.
Trask, L. R. (1996), A Dictionary of Phonetics and Phonology, Routledge.