This book develops the general principles of linguistic change that form the foundations of historical linguistics, dialectology and sociolinguistics. It is concerned with the factors that govern the internal development of linguistic the mechanisms of change, the constraints on change, and the ways in which change is embedded in the larger linguistic system. While it is generally believed that linguistic change is a product of earlier times, and that local dialects are disappearing, this work shows that rapid change is in progress in the cities of America and England, so that urban dialects are becoming more and more differentiated. Instrumental studies of these changes develop a new view of phonological space which allows the resolution of long-standing paradoxes of historical linguistics. The book then develops the general principles governing mergers and splits, which alter linguistic structure.
William Labov was an American linguist widely regarded as the founder of the discipline of variationist sociolinguistics. He has been described as "an enormously original and influential figure who has created much of the methodology" of sociolinguistics, and "one of the most influential linguists of the 20th and 21st centuries". Labov was a professor in the linguistics department of the University of Pennsylvania in Philadelphia and pursued research in sociolinguistics, language change, and dialectology. He retired in 2015 but continued to publish research until his death in 2024.