Principles Old English phonetic changes

The development of vowels in Early OE consisted of the modification of separate vowels, and also of the modification of entire sets of vowels. The change begins with growing variation in pronunciation, which manifests itself in the appearance of numerous allophones: after the stage of increased variation, some allophones prevail over the others and a replacement takes place. It may result in the splitting of phonemes and their numerical growth, which fills in the “empty boxes” of the system or introduces new distinctive features. It may also lead to the merging of old phonemes, as their new prevailing allophones can fall together.