MIDDLE ENGLISH DIPHTHONGIZATION

In the Middle English period, new diphthongs were created by the behavior of the Old English vowels in certain phonetic environments.

1. The development of a glide before the velar fricative /h/.

OE /ah/ > ME /auh/
OE /a:h/ > ME /ôuh/
OE /oh/, /o:h/ > ME /ôuh/
OE /eh/ > ME /æih/
OE /e:h/ > ME /æih/

 

2. Vocalization of /g/ after front vowels.

OE /æg/, /æ:g/ > ME /æi/
OE /eg/ > ME /æi/

 

But note that

OE /ig/, /i:g/ > ME /i:/

 

And

OE /yg/, /y:g/ > ME /i:/, /u:/, /æi/

 

by diphthongization combined with the regular dialectical development of OE /y/, /y:/. See "Unrounding of Vowels."

3. Vocalization of /g/ after back vowels in the middle of a word.

OE /ag/ > ME /au/
OE /a:g/ > ME /ôu/
OE /o:g/ > ME /ôu/

 

But note that

OE /ug/, /u:g/ > ME /u/

 

4. The fusion of a vowel with /w/ in the same syllable.

OE /aw/
>
ME /au/
OE /a:w/
>
ME /ôu/
OE /o:w/
>
ME /ôu/
OE /æ:w/, /æ:'w/
>
ME /eu/
OE /e:'w/
>
ME /iu/
>
ME /eu/
OE /i:w/
>
ME /iu/
>
ME /eu/
(14th c.)