Great Vowel Shift
[4] The Great Vowel Shift was first studied by Otto Jespersen (1860–1943), a Danish linguist and Anglicist, who coined the term.
[5] The causes of the Great Vowel Shift are unknown[6]: 68 and have been a source of intense scholarly debate; as yet, there is no firm consensus.
German had undergone vowel changes quite similar to the Great Shift slightly earlier.
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 vowels occurred in, for example, the words mite, meet, meat, mate, boat, boot, and bout, respectively.
According to Lass, the words bite and out after diphthongisation were pronounced as /beit/ and /out/, similar to American English bait /beɪt/ and oat /oʊt/.
However, many scholars such as Dobson (1968), Kökeritz (1953), and Cercignani (1981) argue for theoretical reasons that, contrary to what 16th-century witnesses report, the vowels /iː uː/ were immediately centralised and lowered to /əi əu/.
[nb 1] Evidence from Northern English and Scots (see below) suggests that the close-mid vowels /eː oː/ were the first to shift.
[16] Modern English typically has the meet–meat merger: both meet and meat are pronounced with the vowel /iː/.
Words like great and steak, however, have merged with mate and are pronounced with the vowel /eɪ/, which developed from the /eː/ shown in the table above.
[21] The first step in the Great Vowel Shift in Northern and Southern English is shown in the table below.
These developments below fall under the label "older" to refer to Scots and a more conservative and increasingly rural Northern sound,[22] while "younger" refers to a more mainstream Northern sound largely emerging just since the twentieth century.
Northern Middle English had two close-mid vowels – /eː/ in feet and /øː/ in boot – which were raised to /iː/ and /yː/.
Southern Middle English had two close-mid vowels – /eː/ in feet and /oː/ in boot – which were raised to /iː/ and /uː/.
In Southern English, shifting of /oː/ to /uː/ could have caused diphthongisation of original /uː/, but because Northern English had no back close-mid vowel /oː/ to shift, the back close vowel /uː/ did not diphthongise.
