Early in Old English (before written records), certain vowels in certain phonetic environments were "broken" into diphthongs.
Certain front vowels followed by certain velar consonants developed a "glide," as the tongue moved from articulating the vowels at the front of the mouth to articulating the consonants at the back of the mouth. The result was the production of a diphthong in the place of the "pure" vowel.
OE vowels followed by the OE velar consonants /h/, /l/, /r/, and /w/ broke according to the following rules.
| /æ/, /æ:/ |
>
|
/æ'/, /æ:'/ | ||
| /e/ |
>
|
/e'/ | ||
| /i/, /i:/ | > |
/i'/,
/i:'/
|
> | /e'/, /e:'/ |