The Great Vowel Shift refers to the 15th century change in pronunciation of long vowels that occurred in England. After this event, vowel pronunciation shifted up one place. So, for example, the "i" in Middle English had a long "e" sound, as in the word "sweet." Afterward, the long "i" sound was pronounced as it is currently, such as in the word "night."
The reasons behind this shift are something of a mystery, and linguists have been unable to account for why it took place. It was first identified and studied by Otto Jesperson, a linguist from Denmark, during the late 19th and early 20th centuries.
Most linguists agree that the Great Vowel Shift did not occur all at once, which accounts for the creative spellings of many English words. Some printers might still have employed an earlier vowel pronunciation when spelling, making English one of the most challenging languages to spell, because so many exceptions to spelling rules exist.
Some linguists account for the change by suggesting that England’s rule by the French led to disenchantment with French pronunciation of vowels, which is a similar pronunciation to that of Middle English. To distance themselves from prior French occupation and rule, the English ruling class may have deliberately changed the ways vowels were pronounced to reflect that theirs was a different language. This then filtered down to the lower classes.
Another theory is that England may have had several influential people with speech impediments, and such mispronunciations might be copied in deference to someone of high enough rank. This theory is not endorsed by many, but does show linguists attempting to consider all possible explanations for the change. The theories regarding the Great Vowel Shift are merely conjectures, but most linguists lean toward the former theory above.
The key pronunciation features of the Great Vowel Shift are the following:
- Middle English (ME) "a" is pronounced as the "a" in "father." Early modern English (EME) pronounces the long "a" as in "gate."
- ME pronounces the long "e" as the long "a" in "gate." EME pronounces the long "e" as the "e" in "tweet."
- ME pronounces the long "i" as the "e" in "tweet." EME pronounces the long "i" as the "i" in "light."
- ME pronounces the long "o" as the "o" in "tool." EME pronounces the long "o" as the "o" in "goal."
ME scholars suggest that no higher long "u" pronunciation exists. The "ou" as in current "day," would have given the "ow" sound, as in the word "louse." EME pronounces the "u" as long "o" in ME. Long "u" pronunciation in EME is as the long "o" of "tool" or the long "u" of "lute."
There are naturally pronunciation exceptions, such as the words "tool" and "lute." Why words with the same essential sound are spelled different suggests that the Great Vowel Shift was certainly not uniform, and did occur over time. Theoretically, "tool" could reasonably be spelled "tule," as is "mule." Whatever the theory, linguists look to the shift as the forebear of modern English pronunciation, and also as to why English speakers spell so many words in ways that make little sense from a phonetic standpoint.