Development of diphthongs

The PG diphthongs – [ei, ai, iu, eu, au] – underwent regular independent changes in Early OE; they took place in all phonetic conditions irrespective of environment. The diphthongs with the i-glide were monophthongised into [i:] and [a:], respectively; the diphthongs in –u were reflected as long diphthongs [io:], [eo:] and [ea:].

Assimilative vowel changes: Breaking and Diphthongization

The tendency to assimilative vowel change, characteristic of later PG and of the OG languages, accounts for many modifications of vowels in Early OE. Under the influence of succeeding and preceding consonants some Early OE monophthongs developed into diphthongs. If a front vowel stood before a velar consonant there developed a short glide between them, as the organs of speech prepared themselves for the transition from one sound to the other. The glide, together with the original monophthong formed a diphthong. The front vowels [i], [e] and the newly developed [æ], changed into diphthongs with a back glide when they stood before [h], before long (doubled) [ll] or [l] plus another consonant, and before [r] plus other consonants, e.g.: [e] > [eo] in OE deorc, NE dark. The change is known as breaking or fracture. Breaking produced a new set of vowels in OE – the short diphthongs [ea] and [eo]; they could enter the system as counterparts of the long [ea:], [eo:], which had developed from PG prototypes. Breaking was unevenly spread among the OE dialects: it was more characteristic of West Saxon than of the Anglian dialects. Diphthongisation of vowels could also be caused by preceding consonants: a glide arose after palatal consonants as a sort of transition to the succeeding vowel. After the palatal consonants [k’], [sk’] and [j] short and long [e] and [æ] turned into diphthongs with a more front close vowel as their first element, e.g. OE scæmu > sceamu (NE shame). In the resulting diphthong the initial [i] or [e] must have been unstressed but later the stress shifted to the first element, which turned into the nucleus of the diphthong, to conform with the structure of OE diphthongs. This process is known as “diphthongisation after palatal consonants”.

Palatal mutation

Mutation is the change of one vowel to another through the influence of a vowel in the succeeding syllable. The most important series of vowel mutations, shared in varying degrees by all OE languages (except Gothic), is known as “i-Umlaut” or “palatal mutation”. Palatal mutation is the fronting and raising of vowels through the influence of [i] or [j] in the immediately following syllable. The vowel was fronted and made narrower so as to approach the articulation of [i]. Due to the reduction of final syllables the conditions which caused palatal mutation, that is [i] or [j], had disappeared in most words by the age of writing; these sounds were weakened to [e] or were altogether lost. The labialized front vowels [y] and [y:] arose through palatal mutation from [u] and [u:], respectively, and turned into new phonemes, when the conditions that caused them had disappeared (cf. mūs and mўs). The diphthongs [ie, ie:] were largely due to palatal mutation and became phonemic in the same way, though soon they were confused with [y, y:]. Palatal mutation led to the growth of new vowel interchanges and to the increased variability of the root-morphemes: owing to palatal mutation many related words and grammatical forms acquired new root-vowel interchanges. We find variants of morphemes with an interchange of root-vowels in the grammatical forms mūs, mўs (NE mouse, mice), bōc, bēc (NE book, books), since the plural was originally built by adding –iz. (Traces of palatal mutation are preserved in many modern words and forms, e.g. mouse – mice, foot – feet, blood – bleed; despite later phonetic changes, the original cause of the inner change is i-umlaut).