Synchronic sociolinguistics has been particularly convincing in its use of quantitative models to demonstrates how ‘the present might explain the past’. However, the relevance of sociolinguistics to historical linguistics ‘using the past to explain the present’, has been largely ignored. In this volume Dr. Romaine lays the foundation for a field of research encompassing both historical linguistics and sociolinguistics, which aims to investigate and account for language variation within a particular speech community over time. The socio-historical approach is illustrated here by a detailed analysis of the development of relative clause formation strategies in Middle Scots. This case study raises fundamental questions about the epistemological status of sociolinguistic theory and in particular its claims to an empirical foundation. Her own preliminary suggestions for a truly integrative sociolinguistic theory will be of interest to sociolinguists, historical linguists and general linguists.