The central doctrine of empiricism, that true knowledge or understanding of the world comes ultimately from sense impressions, underlies most of the practices and arguments of professional historians, but many historians have denied that there is a theory behind what they do. Since the 1980s, however, postmodernism has had a powerful effect on the discipline of history and is now forcing empiricist historians to articulate their methods, and to defend them as both possible and virtuous. In this introduction, Stephen Davies explains what historians mean by empiricism, examines the origins, growth and persistence of empirical methods, and shows how students can apply these methods to their own work.