Great Vowel Shift Definition

The complex series of sound developments (c. 1400 to c. 1750) which changed the vowel system of Middle English into that of Modern English: Middle English long high vowels (ē and ) changed to Modern English diphthongs (ī and ), and long mid and low vowels (ā, ō, and ä) were raised in their tongue positions to the Modern English sounds (ē, , and ā), but the orthography remained largely the same.