Diphthongs

ea
ie *ealdira > OE eald, ieldra (old – elder)
eo
Note: As seen from the examples, after [i] or [j] had produced the mutation, they were frequently lost.

Since the sounds [i] and [j] were common in suffixes and endings, palatal mutation was of very frequent occurrence. Practically all Early OE monophthongs, as well as diphthongs except the closest front vowels [e] and [i] were palatalized in these phonetic conditions.

The palatal mutation has left many traces in Modern English. The vowel interchange serves now to distinguish:

1. different parts of speech:
doom - to deem, food - to feed, blood - to bleed, full - to fill, Angles - English, long- length;

2. different forms of a word:
tooth - teeth, goose - geese, foot - feet, mouse - mice (OE mus - mys), old - elder.

5. VELAR MUTATION

This is another regressive assimilation, also called “back mutation”, as it was caused by back vowels (u, o, a) of the following syllable. The essence of back mutation is this. Under the influence of u, o, a the front vowels I, e, e of a preceding syllable were usually diphthongized.

i > io OE silufr > siolufr > siolfor (silver)
e > eo OE hefun > heofon (heaven)
e > ea OE c eru > cearu (care)

As we see, the assimilation was partial, since only part of the front vowels became velar. But after the sound [w] full assimilation occurred.

OE widu > wudu (wood)
OE werold > worold (world)

Back mutation did not spread equally to all OE dialects and was of comparatively importance for the further development of the English language.

6. THE LENGTHENING OF SHORT VOWELS BEFORE CERTAIN CONSONANT COMBINATIONS

In the 9th century short vowels were lengthened before the combinations ld, nd and mb, i.e. a sonorous consonant plus a homorganic voiced plosive. If, however, the combination was followed by another consonant, the lengthening did not take place. The characteristic feature of the combinations in question is that both consonants are articulated by the same speech organ and that they are both voiced (so-called homorganic combinations).