vowel harmony: an historical account

All languages change over time. English has undergone continuous change throughout its three major periods: Old English (roughly from 450 to 1100 AD), Middle English (from 1100 to 1500), and Modern English (from 1500 to the present). Sound is one of the most easily influenced parts of language to be subject to different changes.  Sound change is inevitable and it is a live indication of the continuous growth of language. The evidence to prove the regularity and systematicity of sound change has been the main concern of linguists, This paper seeks to provide more evidence on how vowel harmony played a key role on the regularity of sound change by extracting samples of sound changes that have taken place throughout the English history.