Great Vowel Shift

The Great Vowel Shift was a series of pronunciation changes in the vowels of the English language that took place primarily between the 1400s and 1600s, beginning in southern England and having influenced effectively all dialects of English today. Through this extensive vowel shift, the pronunciation of all Middle English long vowels altered. Some consonant sounds also changed, specifically becoming silent; the term Great Vowel Shift is occasionally used to include these consonantal changes.
The standardization of English spelling began in the 15th and 16th centuries; the Great Vowel Shift is the major reason English spellings now often deviate considerably from how they represent pronunciations.
Notable early researchers of the Great Vowel Shift include Alexander J. Ellis, in On Early English Pronunciation, with Especial Reference to Shakspere and Chaucer ; Henry Sweet, in A History of English Sounds ; Karl Luick from Vienna, in a series of works dating from 1892 and Untersuchungen zur englischen Lautgeschichte ; and Otto Jespersen who first produced a diagram for it and who in Part I of A [Modern English Grammar on Historical Principles] coined the term.

Causes

The causes of the Great Vowel Shift are unknown and have been a source of intense scholarly debate; as yet, there is no firm consensus. The greatest changes occurred during the 15th and 16th centuries, and their origins are at least partly phonetic.

Population migration: Some scholars have argued that the rapid migration of people to the southeast of England from the East of England and the East Midlands following the Black Death produced a clash of dialects, prompting Londoners to distinguish their speech from that of immigrants arriving from other English cities by changing their vowel system.
French loanwords: Others argue that the influx of French loanwords was a major factor in the shift.
Middle-class hypercorrection: Yet others assert that because of the increasing prestige of French pronunciations among the middle classes, a process of hypercorrection may have started a shift that unintentionally resulted in vowel pronunciations that are inaccurate imitations of French pronunciations.
War with France: An opposing theory states that the wars with France and general anti-French sentiments caused hypercorrection deliberately to make English sound less like French.

Overall changes

The main difference between the pronunciation of Middle English in the year 1400 and Modern English is in the value of the long vowels.
Long vowels in Middle English had "continental" values, much like those in Italian and German phonology#Vowels|Standard German]; in standard Modern English, they have entirely different pronunciations. The differing pronunciations of English vowel letters do not stem from the Great Shift as such but rather because English spelling did not adapt to the changes.
German had undergone vowel changes quite similar to the Great Shift slightly earlier. Still, the spelling was changed accordingly.

Timeline

This timeline uses representative words to show the main vowel changes between late Middle English in the year 1400 and Received Pronunciation in the mid-20th century. The Great Vowel Shift occurred in the lower half of the table, between 1400 and 1600–1700, so the changes after 1700 are not considered part of it. Pronunciation is given in the International Phonetic Alphabet:
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Details

Middle English vowel system

Before the Great Vowel Shift, Middle English in Southern England had seven long vowels,. The vowels occurred in, for example, the words mite, meet, meat, mate, boat, boot, and bout, respectively.

	front	back
close	: mite	: bout
close-mid	: meet	: boot
open-mid	: meat	: boat
open	: mate	—

The words had very different pronunciations in Middle English from those in Modern English:

Long i in mite was pronounced as, so Middle English mite sounded similar to Modern English meet.
Long e in meet was pronounced as, so Middle English meet sounded similar to modern Australian English met but pronounced longer.
Long a in mate was pronounced as, with a vowel similar to the broad a'' of ma.
Long o in boot was pronounced as, so Middle English boot sounded similar to modern Southern England, Australian and New Zealand English bought.

In addition, Middle English had:

Long in meat, like Received Pronunciation air, or modern short e'' in met but pronounced longer.
Long in boat, with a vowel similar to aw in modern Northern England English law, or like modern Southern England, Australian and New Zealand English bot but pronounced longer.
Long in bout, similar to Modern English boot.

Changes

After around 1300, the long vowels of Middle English began changing in pronunciation as follows:

Diphthongisation – The two close vowels,, became diphthongs.
Vowel raising – The other five,, underwent an increase in tongue height.

These changes occurred over several centuries and can be divided into two phases. The first phase affected the close vowels and the close-mid vowels : were raised to, and became the diphthongs or. The second phase affected the open vowel and the open-mid vowels : were raised, in most cases changing to.
The Great Vowel Shift changed vowels without merger, so Middle English before the vowel shift had the same number of vowel phonemes as Early Modern English after the vowel shift.
After the Great Vowel Shift, some vowel phonemes began merging. Immediately after the Great Vowel Shift, the vowels of meet and meat were different, but they are merged in Modern English, and both words are pronounced as.
However, during the 16th and the 17th centuries, there were many different mergers, and some mergers can be seen in individual Modern English words like great, which is pronounced with the vowel as in mate rather than the vowel as in meat.
This is a simplified picture of the changes that happened between late Middle English, Early Modern English, and today's English. Pronunciations in 1400, 1500, 1600, and 1900 are shown. To hear recordings of the sounds, click the phonetic symbols.
Before labial consonants and also after, did not shift, and remains as in soup.

First phase

The first phase of the Great Vowel Shift affected the Middle English close-mid vowels, as in beet and boot, and the close vowels, as in bite and out. The close-mid vowels became close, and the close vowels became diphthongs. The first phase was completed in 1500, meaning that by that time, words like beet and boot had lost their Middle English pronunciation and were pronounced with the same vowels as in Modern English. The words bite and out were pronounced with diphthongs, but not the same diphthongs as in Modern English.
Scholars agree that the Middle English close vowels became diphthongs around 1500, but disagree about what diphthongs they changed to. According to Lass, the words bite and out after diphthongisation were pronounced as and, similar to American English bait and oat. Later, the diphthongs shifted to, then, and finally to Modern English. This sequence of events is supported by the testimony of orthoepists before Hodges in 1644.
However, many scholars such as,, and argue for theoretical reasons that, contrary to what 16th-century witnesses report, the vowels were immediately centralised and lowered to.
Evidence from Northern English and Scots suggests that the close-mid vowels were the first to shift. As the Middle English vowels were raised towards, they forced the original Middle English out of place and caused them to become diphthongs. This type of sound change, in which one vowel's pronunciation shifts so that it is pronounced like a second vowel, and the second vowel is forced to change its pronunciation, is called a push chain.
However, according to professor Jürgen Handke, for some time, there was a phonetic split between words with the vowel and the diphthong, in words where the Middle English shifted to the Modern English. For an example, high was pronounced with the vowel, and like and my were pronounced with the diphthong. Therefore, for logical reasons, the close vowels could have diphthongised before the close-mid vowels raised. Otherwise, high would probably rhyme with thee rather than my. This type of chain is called a drag chain.

Second phase

The second phase of the Great Vowel Shift affected the Middle English open vowel, as in mate, and the Middle English open-mid vowels, as in meat and boat. Around 1550, Middle English was raised to. Then, after 1600, the new was raised to, with the Middle English open-mid vowels raised to close-mid.

Later mergers

During the first and the second phases of the Great Vowel Shift, long vowels were shifted without merging with other vowels, but after the second phase, several vowels merged. The later changes also involved the Middle English diphthong, as in day, which often monophthongised to, and merged with Middle English as in mate or as in meat.
During the 16th and 17th centuries, several different pronunciation variants existed among different parts of the population for words like meet, meat, mate, and day. Different pairs or trios of words were merged in pronunciation in each pronunciation variant. Four different pronunciation variants are shown in the table below. The fourth pronunciation variant gave rise to Modern English pronunciation. In Modern English, meet and meat are merged in pronunciation and both have the vowel, and mate and day are merged with the diphthong, which developed from the 16th-century long vowel.
Modern English typically has the meet–''meat merger: both meet and meat are pronounced with the vowel. Words like great and steak, however, have merged with mate'' and are pronounced with the vowel, which developed from the shown in the table above. Before historic some of these vowels merged with,,,

Northern English and Scots

The Great Vowel Shift affected other dialects and the standard English of southern England but in different ways. In Northern England, the shift did not operate on the long back vowels because they had undergone an earlier shift. Similarly, the dialect in Scotland had a different vowel system before the Great Vowel Shift, as had shifted to in Early Scots. In the Scots equivalent of the Great Vowel Shift, the long vowels, and shifted to, and by the Middle Scots period and remained unaffected.
The first step in the Great Vowel Shift in Northern and Southern English is shown in the table below. The Northern English developments of Middle English and were different from Southern English. In particular, the Northern English vowels in bite, in feet, and in boot shifted, while the vowel in house did not. These developments below fall under the label "older" to refer to Scots and a more conservative and increasingly rural Northern sound, while "younger" refers to a more mainstream Northern sound largely emerging just since the twentieth century.
The vowel systems of Northern and Southern Middle English immediately before the Great Vowel Shift were different in one way. In Northern Middle English, the back close-mid vowel in boot had already shifted to front , like the long ö in German "hear". Thus, Southern English had a back close-mid vowel, but Northern English did not:

In Northern and Southern English, the first step of the Great Vowel Shift raised the close-mid vowels to become close. Northern Middle English had two close-mid vowels – in feet and in boot – which were raised to and. Later on, Northern English changed to in many dialects, so that boot has the same vowel as feet. Southern Middle English had two close-mid vowels – in feet and in boot – which were raised to and.
In Southern English, the close vowels in bite and in house shifted to become diphthongs, but in Northern English, in bite shifted but in house did not.
If the vowel systems at the time of the Great Vowel Shift caused the difference between the Northern and Southern vowel shifts, did not shift because there was no back mid vowel in Northern English. In Southern English, shifting of to could have caused diphthongisation of original, but because Northern English had no back close-mid vowel to shift, the back close vowel did not diphthongise.