The Great Vowel Shift was a series of changes in the pronunciation of the English language that took place primarily between 1400 and 1700, beginning in southern England and today having influenced effectively all dialects of English. Through this vowel shift, the pronunciation of all Middle English long vowels was changed. Some consonant sounds changed as well, particularly those that became silent; the term Great Vowel Shift is sometimes used to include these consonantal changes.
The standardization of English spelling began in the 15th and 16th centuries, and the Great Vowel Shift is the major reason English spellings now often deviate considerably from how they represent pronunciations. The Great Vowel Shift was first studied by Otto Jespersen (1860–1943), a Danish linguist and Anglicist, who coined the term.
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