This is a unified account of all quantity changes affecting English stressed vowels during the early Middle English period. Dr Ritt discusses homorganic lengthening, open syllable lengthening, trisyllabic shortening, and shortening before consonant clusters. The study is based on a statistical analysis of Modern English reflexes of the changes. The complete corpus of analysed data is made available to the reader in the appendices. All of the changes discussed are shown to derive from basically the same set of quasi-universal tendencies, while apparent idiosyncrasies are shown to follow from factors that are independent of the underlying tendencies themselves. The role of tendencies, i.e. probabilistic laws in the description of language change, is given thorough theoretical treatment. In his aim to account for the changes as well as trace their chronology, Dr Ritt applies principles of natural phonology, and examines the conflict between phonological and morphological 'necessities'.