||In OE, refers to a-mutation and u-mutation: the breaking of æ > ea; e > eo; i > io (later eo) in case of a following /a/ or /u/ (in the early stages of OE; /u/ often manifested as <o> in writing): scædu > sceadu; efor > eofor; sifon > siofon
||The development of one vowel into two. In OE, this occurs under influence of a back vowel in the next syllable (in which case the process is referred to as back mutation) or certain following consonants/clusters.
||In OE, refers to i-mutation and j-mutation: the fronting of a back vowel, or raising of a front vowel, under influence of an /i/ or /j/ in the next syllable: u > y; o > e; a > æ (but > e before a nasal); æ > e; e > i; ea, eo > ie: *cuning > cyning; fōt → fēt; mann → menn. The /i/ <i> or /j/ <j> is often subsequently lost.
||The substitution of a back vowel for a front vowel. In OE, the sequence is æ > a; e > o; i > u under influence of a back vowel in the next syllable. Especially common for æ and in Anglian: hældan > haldan