The detailed quantitative study of language change, as found in studies such as Labov (1994) and Kroch (1989), has raised two central questions for linguistic theory. The first is an issue in the theory of language change itself, namely: do changes in different components of the grammar progress in the same way? The second question addresses the relationship between the study of change and the development of synchronic linguistic theory: can quantitative, diachronic data help to choose between alternative analyses of synchronic facts? This paper addresses both of these questions with the case study of the loss of word-final stop fortition (frequently termed "devoicing") in the history of German, and concludes that the answer to both questions above is "yes".