OE vowels were symmetric. There were a correlation of long and short vowels. The system of vowels in OE was inherited from Common Germanic and proto-Indo-European languages.
The sources of OE vowels are common IE with some examples:
1. OE y resulted from palatal mutation from ǔū. E.g. Gth. wulla – OE wyllen.
2. Some OE vowels both monophthongs and diphthongs do not correspond to Gothic and common Germanic vowels because they resulted in English from mutation and there were in OE several similar vowels from different sources. E.g. Gth. sandjan > OE sendan. Gth. stilan > OE stelan. Gth. bairan > OE beran.
3. Before nasals there could be in OE interchangeable vowels a and o which renders instability of pronunciation in OE. E.g. OE stan could be met in OE vowel a with another vowel.
4. OE diphthons are role new formations only to them correspondent to Gothic diphthongs eo, ea || úi, aú. E.g. Gth. kiusan kaus || OE ceosan ceas ‘choose’. German gradation formular is broken and new diphthongs appeared.
5. Other OE diphthongs ie, io appeared as a result of assimilation. OE vowels changed considerably in comparison with other Germanic languages. English vocalic system often shifted throughout the history. These shifts took place in stressed vowels and were conditioned by the fact that long vowels do not preserve their quality and English had a strong tendency to adjust vowel pronunciation to that of the neighboring sounds.
6. Unstressed vowels were reduced due to the strong dynamic stress; beginning from the end of the OE period this reduction is registered but often spelling was traditional.
All OE vowel, including diphthongs, can be either short or long
Monophthongs: a æ e i o u y å Diphthongs: ea eo ie io
_ _ _ _ _ _ _ __ __ __ __
a æ e i o u y ea eo ie io
All diphthongs were falling, that is, the main syllabic element was their first component.
ā may occur in any type of syllable. It corresponds to Gth. ai, e.g. stān ‘stone’ (Gth. stains), hātan ‘call’ (Gth. haitan), cnāwan ‘know’.
æ has a twofold origin.
1. æ1 corresponds to Gth. ē. It is found, for example, in the past plural of class IV and class V strong verbs: stælon ‘stole’ (Gth. stēlum), bæron ‘bore’ (Gth. bērum), spræcon ‘spoke’, mæton ‘measured’, and also in other cases , as I dæd ‘deep’ (Gth. dēþs).
2. æ2 is the result of I’mutation of ā, which corresponds to Gth. ai. It is found in a number of class I weak verbs: hælan ‘heal’ (Gth. hailjam), dræfan ‘drive’, læfan ‘leave’.
ē is usually the result of i-mutation of ō; it is often found in class I weak verbs: dēman ‘judge’, cēpan ‘keep’.
ī may be stable and unstable.
Stable ī usually corresponds to Gth. ei (pronounced [ī]). It is found in class I strong verbs, as in wrītan ‘write’, bīdan ’bide’, ripan ‘catch’. Unstable ī results from ie and alternates with y, e.g. hī ‘they’ (hīe, hy).
ō usually corresponds to Gth. o, as in ōd ‘good’ (Gth. gōþs); it is found in the past tense of class VI strong verbs: scōc ‘shook’, hlōh ‘laughed’.
ū usually corresponds to Gth. ū, e.g., nū ‘now’, hūs ‘house’ (Gth. hūs), and occurs in the infinitive of a few class II strong verbs: lūcan ‘lock’, bū an ‘bend’.
y can be stable and unstable. Stable y in most cases results from i-mutation of ū, as in mys ‘mice’, fyr ‘fire’.
The short diphthongs ea, eo, io, ie, and the long diphthong īe result from mutation, fracture, and palatalization. The long diphthongs ea and eo corresponds to Gothic diphthongs. Ea usually corresponds to Gth. au. It is found in bēam ‘beam’, dēaþ ‘death’ (Gth. dauþus), and also in the past singular of class II strong verbs, as in cēas ‘chose’ (Gth. kaus), lēac ‘locked’ (Gth. lauk).
eo usually corresponds to Gth. iu. It is found in the infinitive of class II strong verbs: cēosan ‘choose’ (Gth. kiusan), bēodan ‘offer’ (Gth. biudan).
io is in most cases a variant of eo.