 Hi, this unit introduces the ways vowel systems organize themselves and it discusses the basic principles of sound change using examples from various dialects of English including historical data. In the virtual session with its question sheet as default guidance, we will start with vowel systems and principles of patterning. We will discuss several types of sound change and will eventually deal with the most important system effects. This includes the great vowel shift, the most well-known system effect the English language underwent. The mastery worksheet is a dynamic multiple choice test with questions about types of sound change using several examples from present day English and the practical presents data from various stages of English to explore the principles of sound shift even more deeply. So this unit provides the background for the study of phonological dialects into historical principles of sound change extremely important for further studies into dialectology.