In Old English, certain front vowels preceded by alveopalatal consonants developed a glide, becoming diphthongs. This phenomenon affects only vowels in stressed syllables, and only those vowels preceded by /j/, /c</, or /s</.

Palatal diphthongization produced the following results.



By the 9th century, however, the /i'/ and /i:'/ resulting from palatal diphthongization had begun to fall together with /i/ and /i:/, respectively, and the diphthongs /i'/ and /i:'/ were lost by the 10th century. (Consequently, these diphthongs are not included in the catalog of OE phonemes presented here.)