The Great Vowel Shift was a historical event that occurred around the 15th century. The way vowels in English words were pronounced changed quite a bit, especially the way long vowels were pronounced. Linguists know this happened from a variety of sources, such as rhyming songs and poetry and the way words were spelled. Spelling is a big clue, even spelling mistakes, because often people make spelling errors that are phonetic, or according to the way words sound or are pronounced. We are not exactly sure the reason this happened, but there are many theories, including movement of the English people, political changes or even people copying speech impediments, or problems, of influential rulers. Whatever the reason, the result for us today in Modern English makes for some unusual spelling and pronunciation rules.
Change is nothing unusual in the history of the English language. For example, the ‘K’ sound was voiced in Old English, not silent, like it is today in Modern English. That is where the spelling of words such as knee, knife or knit with a ‘K’ came from. (Spelling a word with a silent letter is called an aphthong). While the disappearance of the ‘Kn’ sound is not a vowel sound that is part of The Great Vowel Shift, this dramatic change illustrates how pronunciation changes complicate the language.
Let’s look at some examples of vowel changes to better understand The Great Vowel Shift: Home used to rhyme with gloom, ‘boiled’ used to be ‘byled’, ‘join’ was ‘gine’, and ‘work’ was pronounced ‘wark’. In Geoffrey Chaucer’s classic work of literature, Canterbury Tales, ‘oo’ words all rhymed with ‘food’. ‘Tough’ had a guttural ‘o’ sound that was pronounced just as we still spell it.
While some of the spellings have changed to reflect the modern pronunciation, not all of them have. Also, some pronunciations of vowel sounds were not consistent because of regional variations, and this makes it difficult to have pronunciation and spelling rules that do not contain exceptions. Even in Modern English, you will find regional variations of the pronunciation of vowels related to accents. For example in American English, there are different ways to pronounce words such as ‘roof’ (it can rhyme with ‘stuff’ or ‘booth’), ‘route’ (it can rhyme with ‘about’ or ‘boot’) and ‘water’ (it can rhyme with ‘rudder’ or ‘hotter’).