Within each section, changes are in approximate chronological order.

NOTE: In the following description, abbreviations are used as follows:

• OE = Old English
• PreOE = Pre-Old English
• ME = Middle English
• NE = Modern English
• PG = Proto-Germanic
• PrePG = Pre-Proto-Germanic
• NWG = Northwest Germanic
• OHG = Old High German
• MHG = Middle High German
• NHG = Modern German
• Goth = Gothic
• PN = Proto-Norse
• ON = Old Norse
• OS = Old Saxon
• PIE = Proto-Indo-European

The time periods for many of the following stages are extremely short due to the extensive population movements occurring during the early AD period, which resulted in rapid dialect fragmentation:

• The migration of the Goths from southeast Sweden to the Baltic Sea area around AD 1, followed by the migration to southeast Romania around AD 200. (Later migrations carried the Ostrogoths eastward to the Crimea area in modern Ukraine, and carried the Visigoths westward to Spain.)
• The migration of the High German ancestors southward, starting around AD 260, and renewed in the 5th century AD.
• The migration of the Anglo-Saxons westward into Britain, starting around AD 450.

Late Proto-Germanic period (c. AD 0–200)

This includes changes in late Proto-Germanic, up to the appearance of Proto-West-Germanic c. AD 200:

• Early i-mutation: is raised to when an or follows in the next syllable.
  • This occurs before deletion of any unstressed vowels; hence PIE > PG > > Goth "(he) carries".
  • The produced by this change can itself trigger later i-mutation. Hence WG > > OE "(he) carries".
• a-mutation: is lowered to when a non-high vowel follows in the next syllable.
  • This is blocked when followed by a nasal followed by a consonant, or by a cluster with in it. Hence PG > OE/NE gold, but PG > OE gyldan > NE gild.
  • This produces a new phoneme , due to inconsistent application and later loss of unstressed and .
• Loss of before , with nasalization and compensatory lengthening of the preceding vowel.
  • The nasalization was eventually lost, but remained through the Ingvaeonic period.
  • Hence PrePG > PG > > OE þencan think, but PrePG > PG > > OE > NE thought.
• Loss of final , with nasalization (eventually lost) of the preceding vowel. Hence PrePG > PG > PN > WG "day (acc. sg.)".
• Pre-nasal raising: > before nasal + consonant. PrePG > PG > > OE bindan > NE bind (Latin ).
  • This post-dated lost of before .
  • This was later extended in PreOE times to vowels before all nasals; hence OE niman "take" but OHG neman.
• > (c. AD 100). The Elder Futhark of the Proto-Norse language still contain different symbols for the two sounds.
• Vowels in unstressed syllables were reduced or eliminated. The specifics are quite complex and occurred as a result of many successive changes, with successive stages often happening hundreds of years after the previous stage. Some specifics of the initial stage:
  • Final-syllable short vowels inherited from Proto-Germanic were generally deleted. Hence Goth "(he) carries" < PG (see above).
    • This operated universally only in words of three syllables or more. In words of two syllables, final-syllable and were deleted, but and were unaffected following a short syllable (i.e. one with a short vowel followed by a single consonant.) Hence PG > Goth dags "day (nom. sing.)" (OE dæg), PIE > PG > Goth wáit "(I) know" (OE ), PIE > PG > Goth "wáit" "(he) knows" (OE ); but PIE > PG > Goth sunus "son (nom. sing.)" (OE sunu), PIE > PG > Goth faíhu "cattle (nom. sing.)" (OE feohu), PIE > PG > > OHG wini "friend (nom. sing.)" (OE wine), PIE > PG > PreOE > OE "foot (dat. sing.)".
    • Final-syllable and were protected in words of two syllables by following and . Hence PG > NE father; PG > Goth stáinans "stone (acc. pl.)".
    • Final-syllable and in two-syllable words were still present in Proto-Norse. PN , Goth dags "day (nom. sg.)". PN , Goth dag "day (acc. sg.)".
  • Final-syllable long vowels were shortened.
    • But final-syllable becomes in NWG, in Gothic. Hence PG > early OE beru "(I) carry", but Goth baíra; PG > OE giefu "gift (nom. sg.)", but Goth giba.
  • Middle-syllable vowels of all types were unchanged; likewise in monosyllables, since they were stressed.
  • "Extra-long"' vowels were shorted to long vowels. There is a great deal of argument about what is exactly going on here.
    • The traditional view is that a circumflex accent arose (as in Ancient Greek) when two adjacent vowels were contracted into a single long vowel in a final syllable. This circumflexed vowel then remained long when other long vowels shortened.
    • A newer view holds that "overlong" (tri-moraic) vowels arose from the contraction of two vowels, one of which was long. Furthermore, final-syllable long vowels remained long before certain final consonants ( and ).
    • The reason why such theories are necessary is that some final-syllable long vowels are shortened, while others remain. Nominative singular shortens, for example; likewise first singular < ; while genitive plural < remains long. Both of the above theories postulate an overlong or circumflex ending in the genitive plural arising in the vocalic (PIE and , PG and ) declensions, arising from contraction of the vocalic stem ending with the genitive plural ending.
    • Other examples of vowels that remain long are a-stem and ó-stem nominative plural < early PIE and ; PrePG ablative singular , (Gothic "whither", undarō "under"); -stem dative singular PG > Goth gibái "gift" (but -stem dative singular PG > Goth staina "stone").

West Germanic period (c. AD 200–400)

This includes changes up through the split of Ingvaeonic and High German (c. AD 400):

• Unstressed diphthongs were monophthongized. > , > .
  • Results were different in Gothic. Diphthongs remained except for absolutely final diphthongs stemming from PIE short diphthongs, which became short .
  • Hence PIE > PG > Goth sunáus, but > PWG > OE suna "son (gen. sing.)"; PIE > PG > > Goth nimái, but > PWG > OE nime "(he) takes (subj.)"; PIE (loc.?) > PG > Goth staina, but > PWG > OE "stone (dat. sing.)"; PIE (loc.?) > PG > Goth gibái, but > PWG > OE giefe "gift" (dat. sing.).
• becomes .

• Elimination of word-final .
  • Note that this change must have occurred before rhotacization, as original word-final did not become .
  • But it must have occurred after the North-West-Germanic split , since word-final was not eliminated in Old Norse, instead merging with .
• Rhotacization: > .
  • This change also affected Proto-Norse; but in Proto-Norse, the date and nature are contested. and were still distinct in the Danish and Swedish dialect of Old Norse, as is testified by distinct runes. ( is normally assumed to be a rhotic fricative in this language, but there is no actual evidence of this.)
• West Germanic Gemination of consonants except , when preceded by a short vowel and followed by .
  • OE nominative plural (ME ), OS nominative plural may be from original accusative plural (rather than original nominative plural ; cf. ON nominative plural ), following Ingvaeonic nasalization/loss of nasals before fricatives.

Ingvaeonic and Proto-Anglo-Frisian period (c. AD 400–475)

This includes changes from c. AD 400 up through the split of the Anglo-Frisian languages from Ingvaeonic, followed by the split of pre-Old English from pre-Old Frisian (c. AD 475). The time periods for these stages are extremely short due to the migration of the Anglo-Saxons westward through Frisian territory and then across the English Channel into Britain, around AD 450.

• Ingvaeonic nasal spirant law: Loss of nasals before fricatives, with compensatory lengthening. Hence PG > NG mund but OE , NE mouth.
  • An intermediate stage was a long nasal vowel, where nasal > . PIE > PG > OE "tooth". (NHG Zahn < OHG zant.)
• Development of new - distinction through Anglo-Frisian brightening and other changes:
  • Fronting of to (generally, unless followed).
  • Fronting of to (unless followed by a geminate, by a back vowel in the next syllable, or in certain other cases). Hence OE dæg "day", plural dagas "days" (dialectal NE "dawes"; compare NE "dawn" < OE dagung ). Gothic dags, plural .
  • Change of to . PG > OE > NE stone.

Old English period (c. AD 475–900)

This includes changes from the split between Anglo-Saxon and Frisian (c. AD 475) up through historic early West Saxon of AD 900:

• Breaking of front vowels
  • Most generally, before , , + consonant, + consonant (assumed to be velar , in these circumstances), but exact conditioning factors vary from vowel to vowel
  • Initial result was a falling diphthong ending in , but this was followed by Diphthong height harmonization, producing short , , from short , , , long , , from long , , . (Written ea, eo, io, where length is not distinguished graphically.)
  • Result in some dialects, for example Anglian, was back vowels rather than diphthongs. West Saxon ceald; but Anglian cald > NE cold.
• and were lowered to and between 800 and 900 AD.
• By the above changes, was fronted to and then modified to by Diphthong height harmonization.
  • PG > OE "joy" (cf. NE dream, NHG Traum). PG > OE > NE death (Goth , NHG Tod). PG > OE > NE eye (Goth , NHG Auge).
• was palatalized to in almost all circumstances. PG > NE ship (cf skipper < Dutch schipper, where no such change happened). PG > OE scyrte > NE shirt, but > ON skyrt > NE skirt.
• , , were palatalized to , , in certain complex circumstances, described in detail on the Old English page.
  • This change, or something similar, also occurred in Frisian.
• Back vowels were fronted when followed in the next syllable by or , by i-mutation (c. 500 AD).
  • i-mutation affected all the Germanic languages except for Gothic, although with a great deal of variation. It appears to have occurred earliest, and to be most pronounced, in the Schleswig-Holstein area (the home of the Anglo-Saxons), and from there to have spread north and south.
  • This produced new front-rounded vowels , , , . and were soon unrounded to and , respectively.
  • All short diphthongs were mutated to , all long diphthongs to . (This interpretation is controversial. These diphthongs are written ie, which is traditionally interpreted as short , long .)
  • Late in Old English (c. AD 900), these new diphthongs were simplified to and , respectively.
  • The conditioning factors were soon obscured (loss of whenever it had produced gemination, lowering of unstressed ), phonemicizing the new sounds.
• More reductions in unstressed syllables:
  • became .
  • Germanic high vowel deletion eliminated and when following a heavy syllable.
• Palatal diphthongization: Initial palatal , , trigger spelling changes of a > ea, e > ie. It is disputed whether this represents an actual sound change or merely a spelling convention indicating the palatal nature of the preceding consonant (written g, c, sc were ambiguous in OE as to palatal , , and velar or , , , respectively).
  • Similar changes of o > eo, u > eo are generally recognized to be merely a spelling convention. Hence WG > OE geong > NE "young"; if geong literally indicated an diphthong, the modern result would be *yeng.
  • It is disputed whether there is Middle English evidence of the reality of this change in Old English.
• Initial became in late Old English.

Up through Chaucer's English (c. AD 900–1400)

• Vowels were lengthened before , , , , probably also , , , when not followed by a third consonant.
  • This probably occurred around AD 1000.
  • Later on, many of these vowels were shortened again; but evidence from the Ormulum shows that this lengthening was once quite general.
  • Remnants persist in the Modern English pronunciations of words such as child (but not children, since a third consonant follows), field (plus yield, wield), climb, find (plus mind, kind, bind, etc.), fiend, found (plus hound, bound, etc.).
• Vowels were shortened when followed by two or more consonants, except when lengthened as above.
  • This occurred in two stages, the first stage affecting only vowels followed by three or more consonants.
• Inherited height-harmonic diphthongs were monophthongized by the loss of the second component, with the length remaining the same.
• and became and .
• and merged into .
• and were unrounded to and .
• became or , depending on surrounding vowels.
• New diphthongs formed from vowels followed by or (including from former ).
  • Length distinctions were eliminated in these diphthongs.
  • Diphthongs also formed by the insertion of a glide or (after back and front vowels, respectively) preceding .
  • Many diphthong combinations soon merged.
• Trisyllabic laxing: Shortening of stressed vowels when two syllables followed.
  • This results in pronunciation variants in Modern English such as divine vs divinity and south vs. southern (OE súðerne).
• Middle English open syllable lengthening: Vowels were usually lengthened in open syllables (13th century), except when Trisyllabic laxing would apply.
• Remaining unstressed vowels merged into .
• Initial clusters , , were reduced by loss of .
• Voiced fricatives became independent phonemes through borrowing and other sound changes.
• before back vowel becomes ; becomes .
  • Modern English sword, answer, lamb.
  • in swore is due to analogy with swear.

Up to Shakespeare's English (c. AD 1400–1600)

• Loss of most remaining diphthongs.
  • (and former , merged into in Early Middle English) became before the Great Vowel Shift.
  • (and former , merged into in Early Middle English) became and became after the shift causing the long mid mergers.
  • became after the shift.
  • The dew-new merger: and /iu/ merger, and they then become after the shift.
  • The joy-point merger: and /oi/ merge, so that point and joy now have the same vowel.
  • The rein-rain merger: /ai/ and /ei/ merge, so that rain and rein are now homonyms.
  • The dew-duke merger: /y/ and /iu/ merge, so that dew and duke now have the same vowel.
  • remained.
  • A few regional accents, including some in Northern England, East Anglia, South Wales, and even Newfoundland, monophthongization has not been complete, so that pairs like pane/pain and toe/tow are distinct. (Wells 1982, pp. 192–94, 337, 357, 384–85, 498)
• (written gh) lost in most dialects causing the taut-taught merger.
• Great Vowel Shift; all long vowels raised or diphthongized.
  • , , become , , , respectively.
  • , become , , respectively.
  • , become and , later and .
  • New developed from old (see above).
  • Note that , , , effectively rotated in-place.
  • , are shifted again to , in Early Modern English, causing merger of former with ; but the two are still distinguished in spelling as ea, ee.
• Loss of in final syllables.
• Initial cluster loses first element; but still reflected in spelling.
• /kn/ reduces to /n/ in most dialects, causing the not-knot merger.
• /wr/ reduces to /r/ in most dialects, causing the rap-wrap merger.
• Doubled consonants reduced to single consonants.

Up to the American/British split (c. AD 1600–1725)

• At some preceding time after Old English, all become .
  • Evidence from Old English shows that, at that point, the pronunciation occurred only before a consonant.
  • Scottish English has consistently.
• The foot-strut split: Except in northern England, splits into (inconsistently after labials), as in put, (otherwise), as in cut.
• Ng coalescence: Reduction of in most areas produces new phoneme .
• Palatalization of , , , produces , , , and new phoneme (for example measure, vision).
  • These combinations mostly occurred in borrowings from French and Latin.
  • Pronunciation of tion was from Old French , thus becoming .
• Long vowels inconsistently shortened in closed syllables. (Modern English head, breath, bread, blood, etc.)
• The meet-meat merger: Meet and meat become homonyms in most accents.
• Changes affect short vowels in many varieties before an at the end of a word or before a consonant
  • as in start and as in north are lengthened.
  • , and merge, hence most varieties of Modern English have the same vowel in each of fern, fir and fur.
  • Also affects vowels in derived forms, so that starry no longer rhymes with marry.
  • Scottish English unaffected.
• , as in cat and trap, fronted to in many areas.
  • But backed, rounded, and lengthened to before syllable-final (that is, velarized) (). Modern English tall, talk, bald, salt, etc. But in -alm, in -alf.
  • New phoneme develops from (calm ) and in certain other words, for example father .
  • Most varieties of northern English English, Welsh English and Scottish English retain in cat, trap etc.
• Loss of in , , (see above).
• The pane-pain merger: The words pane and pain become homophones in most accents.
• The toe-tow merger: The words toe and tow become homophones in most accents.