How did vowel changes in Middle English contribute to modern spellings?

The Great Vowel Shift (GVS) is a primary reason why modern English spelling often appears unphonetic. Occurring between the 15th and 18th centuries, this series of systematic changes in the articulation of long vowels created a significant disconnect between the way words were written and how they were pronounced.12

Because English spelling was largely standardized based on 15th-century conventions—around the time the printing press was introduced—it became "frozen" even as the actual pronunciation of vowels continued to evolve. During the GVS, long vowels underwent a "chain shift" where the tongue moved to higher positions in the mouth, and high vowels were diphthongized. For example, the Middle English long vowel in sheep (pronounced like modern shape) shifted to the sound heard in beet, yet the spelling remained largely unchanged.132

This shift left many words with "archaic" spellings that no longer reflect their modern sounds. Furthermore, because spelling became fixed during the 17th and 18th centuries, these phonetic changes were never fully integrated into the orthography, resulting in the inconsistent spelling patterns that persist in the English language today.1