During EME, the palatal semivowel EME /j/ was sometimes inserted before the unstressed vowel of a syllable following the stressed syllable. Thus, e.g., EME /presur/ pressure became EME /presjur/; EME /grædu'l/ gradual became EME /grædju'l/.
If the consonant preceding the intrusive /j/ was an /s/, /z/, /t/, or /d/, the consonant combined with the /j/ to produce a palatal fricative or affricate. This phenomenon is called "assibilation." Assibilation produced the following results in EME.
| /dj/ |
>
|
/j</ |
| /sj/ |
>
|
/s</ |
| /tj/ |
>
|
/c</ |
| /zj/ |
>
|
/z</ |
Assibilation is the origin of the phoneme /z</ in EME.