Pronouncing Chaucer's English
Middle English is the form of English used in England from roughly the time of the Norman conquest (1066) until about 1500. After the conquest, French largely displaced English as the language of the upper classes and of sophisticated literature. In Chaucer's time this was changing, and in his generation English regained the status it had enjoyed in Anglo-Saxon times, before the Normans came. English was once again becoming the language of the royal court and of the new literature produced by Chaucer and his contemporaries. (For a more detailed account see the section on Middle English.)
The main difference between Chaucer's language and our own is in the pronunciation of the "long" vowels. The consonants remain generally the same, though Chaucer rolled his r's, sometimes dropped his aitches, and pronounced both elements of consonant combinations (such as "kn-" in knight or "wr-" in write) that were later simplified (to "n-" and "r-"). And the Middle English short vowels are very similar to those in Modern English (Chaucer's "short a" was more like the sound in "rot" than in modern "rat.") But the the Middle English "long" vowels are regularly and strikingly different from our modern forms.
These changes in the pronunciation of the "long vowels" are due to what is called The Great Vowel Shift. Between Middle English times and our own day, all of the long vowels changed in pronunciation in a regular manner, called "The Great Vowel Shift" (learn more here).
Those changes are apparent in the following chart, which also provides a guide to the pronunciation of Chaucer's "long vowels":
Middle English Sounds like Modern
|y,i "myne, sight"||"meet"|
|e, ee "me, meet, mete" (close e)||"mate"|
|e "begge, rede" (open e)||"bag"|
|a, aa "mate, maat"||"father"|
|u, ou "hus, hous"||"boot"|
|o, oo "bote, boot" (close o)||"oak"|
|o "lof, ok" (open o)||"bought"|
For a thorough treatment of Chaucer's pronunciation take time to work your way slowly through the pronunciation exercises.