Phonological history of Old English

The phonological system of the Old English language underwent many changes during the period of its existence. These included a number of vowel shifts, and the palatalisation of velar consonants in many positions.
For historical developments prior to the Old English period, see Proto-Germanic language.

Phonetic transcription

Various conventions are used [|below] for describing Old English words, reconstructed parent forms of various sorts and reconstructed Proto-West-Germanic, Proto-Germanic and Proto-Indo-European forms:

Forms in italics denote either Old English words as they appear in spelling or reconstructed forms of various sorts. Where phonemic ambiguity occurs in Old English spelling, extra diacritics are used.
Forms between /slashes/ or indicate, respectively, broad or narrow pronunciation. Sounds are indicated using standard IPA notation.

The following table indicates the correspondence between spelling and pronunciation transcribed in the International Phonetic Alphabet. For details of the relevant sound systems, see Proto-Germanic phonology and Old English phonology.

Sound	Spelling	Pronunciation
Short vowels	o e etc.	etc.
Short nasal vowels	ǫ ę etc.	etc.
Long vowels	ō ē etc.	etc.
Long nasal vowels	ǭ ę̄ etc.	etc.
Overlong vowels	ô ê
Overlong nasal vowels	ǫ̂ ę̂
"Long" diphthongs	ēa ēo īo īe
"Short" diphthongs	ea eo io ie
Old English unpalatalized velars¹	c sc g ng gg
Old English palatalized velars¹	ċ sċ ġ nġ ċġ
Proto-Germanic velars¹	k sk g; sometimes also ɣ
Proto-Germanic voiced stops/fricatives¹	b d g; sometimes also β, ð or đ, ɣ

¹Proto-Germanic had two allophones each: stops and fricatives. The stops occurred:

following a nasal;
when geminated;
word-initially, for and only;
following, for only.

By West Germanic times, was pronounced as a stop in all positions. The fricative allophones are sometimes indicated in reconstructed forms to make it easier to understand the development of Old English consonants. Old English retained the allophony, which in case of palatalisation became. Later, non-palatalized became word-initially. The allophony was broken when merged with, the voiced allophone of.

Phonological processes

A number of phonological processes affected Old English in the period before the earliest documentation. The processes affected especially vowels and are the reason that many Old English words look significantly different from related words in languages such as Old High German, which is much closer to the common West Germanic ancestor of both languages. The processes took place chronologically in roughly the order described below.

Absorption of nasals before fricatives

This is the source of such alternations as modern English five, mouth, us versus German fünf, Mund, uns. For detail see Ingvaeonic nasal spirant law.

First [|a-fronting]

The Anglo-Frisian languages underwent a sound change in their development from Proto-West-Germanic by which , unless followed by or nasalized, was fronted to . This was similar to the later process affecting short, which is known as Anglo-Frisian brightening or First Fronting. Nasalized ą̄ and the sequences ān, ām were unaffected and were later raised to ǭ, ōn, ōm. In the non-West-Saxon dialects of English the fronted vowel was further raised to ē : W.S. slǣpan, sċēap versus Anglian slēpan, sċēp. The Modern English descendants sleep and sheep reflect the Anglian vowel; the West Saxon words would have developed to *sleap, *sheap.
The vowel affected by this change, which is reconstructed as being a low back vowel ā in Proto-West-Germanic, was the reflex of Proto-Germanic. It is possible that in Anglo-Frisian, Proto-Germanic simply remained a front vowel, developing to Old English ǣ or ē without ever passing through an intermediate stage as the back vowel. However, borrowings such as Old English strǣt from Latin strāta and the backing to ō before nasals are much easier to explain under the assumption of a common West Germanic stage *ā.

Monophthongization

Proto-Germanic was monophthongized to . This occurred after [|first a-fronting]. For example, Proto-Germanic *stainaz became Old English stān . In many cases, the resulting was later fronted to by i-mutation: dǣlan "to divide".
It is possible that this monophthongization occurred via the height harmonisation that produced the other diphthongs in Old English.
A similar sound change has occurred in Southern American English and African-American Vernacular English.

Second a-fronting

The second part of a-fronting, called Anglo-Frisian brightening or First Fronting, is very similar to the [|first part] except that it affects short a instead of long ā. Here a is fronted to æ unless followed by or nasalized, the same conditions as applied in the first part.
Importantly, a-fronting was blocked by n, m only in stressed syllables, not unstressed syllables, which accounts for forms like ġefen "given" from Proto-Germanic *gebanaz. However, the infinitive ġefan retains its back vowel due to a-restoration.

Diphthong height harmonisation

Proto-Germanic had the closing diphthongs . In Old English, these developed into diphthongs of a generally less common type in which both elements are of the same height, called height-harmonic diphthongs. This process is called diphthong height harmonisation. Specifically:

underwent a-fronting to and was then harmonised to, spelled .
was harmonised to, spelled .
was already harmonic; it became a separate phoneme, spelled .

Old English diphthongs also arose from other later processes, such as [|breaking], palatal diphthongisation, [|back mutation] and [|i-mutation], which also gave an additional diphthong ie. The diphthongs could occur both short and long.
Some sources reconstruct other phonetic forms that are not height-harmonic for some or all of these Old English diphthongs. The first elements of ēa, ēo, īo are generally accepted to have had the qualities,, . However, the interpretations of the second elements of these diphthongs are more varied. There are analyses that treat all of these diphthongs as ending in a schwa sound ; i.e. ēa, ēo, īo =. For io and ie, the height-harmonic interpretations and are controversial, with many sources assuming that the pronunciation matched the spelling, and hence that these diphthongs were of the opening rather than the height-harmonic type. In Early West Saxon, and later in Anglian io merged with eo.

Breaking and retraction

in Old English is the diphthongization of the short front vowels to short diphthongs when followed by, or by or plus another consonant. Long similarly broke to, but only when followed by. The geminates rr and ll usually count as r or l plus another consonant, but breaking does not occur before ll produced by West Germanic gemination.
were lowered to in Early West Saxon and late Anglian.
The exact conditions for breaking vary somewhat depending on the sound being broken:

Short breaks before h, rC, lC, where C is any consonant.
Short breaks before h, rC, lh, lc, w, i.e. compared to it is also broken before w, but is broken before l only in the combination lh and sometimes lc.
Short breaks before h, rC, w. However, it does not break before wi, and in the Anglian dialects breaking before rCi happens only in the combination *rzi.
Long ī and ǣ break only before h.

Examples:

weorpan "to throw" <
wearp "threw " <
feoh "money" <
feaht "fought " <
healp "helped " <
feorr "far" <
feallan "to fall" <
eolh "elk" <
liornian, leornian "to learn" < earlier
nēah "near" <
lēon "to lend" < < <

The i-mutation of broken is spelled .
Examples:

hwierfþ "turns" < + i-mutation < + breaking < Proto-Germanic *hwirbiþi < early Proto-Germanic *hwerbiþi
hwierfan "to turn" < + i-mutation < + breaking < + a-fronting < Proto-Germanic *hwarbijaną
nīehst "nearest" < + i-mutation < + breaking < + a-fronting < Proto-Germanic *nēhist
līehtan "to lighten" < + i-mutation < + breaking < Proto-Germanic *līhtijaną

Note that in some dialects was backed to rather than broken, when occurring in the circumstances described above that would normally trigger breaking. This happened in the dialect of Anglia that partially underlies Modern English, and explains why Old English ceald appears as Modern English "cold" rather than "*cheald".
Breaking and retraction commonly explained in terms of assimilation of the vowel to a following velar consonant. While is in fact a velar consonant,,, and are less obviously so. It is therefore assumed that, at least at the time of the occurrence of breaking and retraction, was pronounced or similar – at least when following a vowel – and and before a consonant had a velar or retroflex quality and were already pronounced and, or similar.
disputes the common assumption that postvocalic must have been pronounced as velar at the time of vowel breaking. He argues that this is problematic regardless of which order is assumed for the sound changes of velar palatalization and breaking: if breaking occurred before palatalization and was triggered by, there is no clear explanation for why vowels did not break before the other velar consonants, whereas if breaking occurred after palatalization, there is no clear explanation for why was still velar after front vowels, when the other velar consonants had become palatalized in this position. Howell proposes instead that prior to Old English, *x was originally weakened to in all positions, and that this became strengthened to in the syllable coda later on, perhaps at the time when it merged phonemically with the devoiced outcome of former.
Peter Schrijver has theorized that Old English breaking developed from language contact with Celtic languages. He says that two Celtic languages were spoken in Britain, Highland British Celtic, which was phonologically influenced by British Latin and developed into Welsh, Cornish and Breton, and Lowland British Celtic, which was brought to Ireland at the time of the Roman conquest of Britain and became Old Irish. Lowland British Celtic had velarization like Old and Modern Irish, which gives preceding vowels a back offglide. That feature came by language contact to Old English and resulted in backing diphthongs.