Language change happens in the spatio-temporal world. Historical linguistics is the craft linguists exercise upon its results, in order to tell coherent stories about it. In a series of linked essays Roger Lass offers a critical survey of the foundations of the art of historical linguistics, and its interaction with its subject matter, language change. He takes as his background some of the major philosophical issues which arise from these considerations, such as ontology, realism and conventionalism, and explanation. Along the way he poses such questions as: where does our data come from; how trustworthy is it; what is the empirical basis for the reconstructive techniques we standardly take as yielding facts; and how much does the historian create data rather than receiving it? The paradoxical conclusion is that our historiographical methods are often better than the data they have to work with.