This book develops the general principles of linguistic change that form the foundations of historical linguistics, dialectology and sociolinguistics.  Demonstrates the social as well as cognitive relevance of linguistic researchShows that rapid linguistic change is in progress in the cities of America and England so that urban dialects are becoming more and more differentiatedDiscusses factors that govern the internal development of linguistic structures: the mechanisms of change, the constraints on change, and the ways in which change is embedded in the larger linguistic system