Vowel Shift was a major change in the pronunciation of Germanic languages, generally accomplished in the 15th century and early 16th century, both in Europe and England. It represented a change in the long vowels (i.e. a vowel shift). In English, the shift began toward the end of the 15th century and was mostly completed in the 16th century, although it continued for some time after that, spreading toward the non-metropolitan and non-port areas.

The values of the long vowels form the main difference between the pronunciation of Middle English and Modern English, and the Great Vowel Shift is one of the historical events marking the separation of Middle and Modern English. Originally, these vowels had "continental" values much like those remaining in liturgical Latin. However, during the Great Vowel Shift, the two highest long vowels became diphthongs, and the other five underwent an increase in tongue height and one of them came to the front.

The principal changes are roughly the following — though exceptions occur, the transitions were not always complete, and there were sometimes accompanying changes in orthography:

/a:/ -> /e:/ (in e.g. make)

/E:/ -> /e:/ or /i:/ (in e.g. break, beak)

/e:/ -> /i:/ (in e.g. feet)

/i:/ -> /ai/ (in e.g. mice)

/O:/ -> /o:/ (in e.g. boat)

/o:/ -> /u:/ (in e.g. boot)

/u:/ -> /au/ (in e.g. mouse)

This means that the vowel in the English word make was originally pronounced as in modern English father, but has now become a diphthong, as it is today in standard pronunciations of British English (see Received Pronunciation); the vowel in feet was originally pronounced as a long Latin-like e sound; the vowel in mice was originally what the vowel in feet is now; the vowel in boot was originally a long Latin-like o sound; and the vowel in mouse was originally what the vowel in moose is now, but has now become a diphthong.

The Great Vowel Shift was first studied by the Danish linguist Otto Jespersen (1860 - 1943), who coined the term.

The shift was remarkable for how widespread it was (going through most of Europe and then Great Britain), as well as its rapidity. The effects of the shift were not entirely uniform, and differences in degree of vowel shifting can sometimes be detected in regional dialects, both in written and spoken English. The surprising speed and the exact cause of the shift are continuing mysteries in linguistics and cultural history

. Because English spelling was becoming standardized in the 15th and 16th centuries, the Great Vowel Shift is responsible for many of the peculiarities of English spelling. Spellings that made sense according to Middle English pronunciation were retained in Modern English.

Quantitative vowel changes in early middle english

In later OE and in Early ME vowel length began to depend on phonetic conditions.

The earliest of positional quantitative changes was the readjustment of quantity before some consonant clusters; it occurred in Early ME or perhaps even in Late OE.

The changes of vowel quantity reduced the number of positions in which the opposition of long vowels to short ones could be used for phonemic contrast. Before a consonant cluster vowel quantity was now predetermined by the nature of the cluster; and in open syllables three vowels— [ב:], [a:] and [ε:] were always long. Consequently, opposition through quantity could be used for distinction, as a phonological feature, only in the absence of those phonetic conditions, namely: in closed syllables, in polysyllabic words, or with the vowels [i] and [u] in open syllables. Such is the contrast, e.g. in ME risen ['ri:z∂n] inf. and risen ['ri:z∂n] Part. II (NE rise, risen). The limitations in the application of vowel length as a distinctive feature undermined the role of vowel quantity in the language.

Table 2

Quantitative Vowel Changes in Late Old English and Early Middle English

Quantitative vowel changes in Early ME have given rise to a number of explanations and hypotheses.

All the changes in vowel quantity have been interpreted as manifestations of a sort of rhythmic tendency. In order to achieve an average uniformity in the length of the syllable, and also to use an average amount of energy for its pronunciation, the vowel was shortened before a group of consonants and was made longer if there were no consonants following, that is, in “open” syllables. Lengthening of vowels before homorganic groups looks as an exception or a contradiction; to account for this lengthening it was suggested that -nd, -ld and the like were virtually equivalent to single consonants, therefore a long vowel would not make the syllable too heavy.

This theory was criticised for attributing all the quantitative changes to one general cause — the effort to maintain a uniform syllable length — though in reali­ty the changes were not simultaneous. Lengthening in open syllables occurred at a later period — some time in the 13th c. — and may have been caused by other factors. To cope with this difficulty, it was suggested that lengthening in open syllables was tied up with the weakening of final vowels; when the second, unaccented, syllable was weakened, the first syllable became more prominent and the vowel was made longer. Cf. OE talu and ME tale ['ta:l∂] — the average amount of energy required for the pronunciation of the word is the same but it, distribution is different.

Development of Monophthongs.

As compared with quantitative changes, qualitative vowel changes in Early ME were less important. They affected several mono­phthongs and displayed considerable dialectal diversity. On the whole they were independent of phonetic environment.

The OE close labialised vowels [y] and [y:] disappeared in Early ME, merging with various sounds in different dialectal areas. The treatment of [y] and [y:] in ME can be regarded as evidence of growing dialectal divergence. At the same time it is a relatively rare instance of similar alterations of a short and a long vowel.

Development of Old English [y] and [y:] in Middle English dialects

Examples

In Early ME the long OE [a:] was narrowed to [ב:]. This was an early instance of the growing tendency of all long monophthongs to become closer; the tendency was intensified in Late ME when all long vowels changed in that direction, [a:] became [ב:] in all the dialects except the Northern group.

The short OE [æ] was replaced in ME by the back vowel [a]. In OE [æ] was either a separate phoneme or one of a group of allophones distinguished in writing [æ, a, ã, ea]. All these sounds were reflected in ME as [a], except the nasalised [ã] which became [o] in the West Midlands (and thus merged with a different phoneme lo] or [ב].

OE þæt > ME that [θat] (NE that)

earm > arm [arm] (NE arm)

blacu > blak [blak] (NE black)

The development of OE [as] to ME [a] is viewed with suspicion by some scholars, because the history of this sound includes several reversals, which is hardly probable: PG [a] > OE [æ] > ME [a] > NE [æ]. Perhaps, it was a graphic replacement and the ME letter a stood for two allophones, [æ] and [a].