Recent years have seen intense debates between formal (generative) and functional linguists, particularly with respect to the relation between grammar and usage. This debate is directly relevant to diachronic linguistics, where one and the same phenomenon of language change can be explained from various theoretical perspectives. In this, a close look at the divergent and/or convergent evolution of a richly documented language family such as Romance promises to be useful. The basic problem for any approach to language change is what Eugenio Coseriu has termed the paradox of change: if synchronically, languages can be viewed as perfectly running systems, then there is no reason why they should change in the first place. And yet, as everyone knows, languages are changing constantly. In nine case studies, a number of renowned scholars of Romance linguistics address the explanation of grammatical change either within a broadly generative or a functional framework.