This book seeks to answer the questions: why do grammars change, and why is the rate of such change so variable? A principal focus is on changes in English between the Anglo-Saxon and early modern periods. The author frames his analysis in a comparative framework with extended discussions of language change in a wide range of other Indo-European languages. He deploys Chomsky's minimalist framework in a fruitful marriage of comparative and theoretical linguistics within an argument that will be accessible to practitioners in both fields.