Abstract
The chapter looks at language variation and change, and the relation of these processes to language reconstruction and classification. The chapter gives an overview of theories, models, methods, and data, describing how diversity and variation is modelled and measured for reconstruction and classification within traditional, comparative and statistical, evolutionary, or phylogenetic methods. First, the chapter identifies the basic principles of language change and the way in which these differ within various subdomains of language. A second part delves into the outcomes of change, describing the diverse results of sound change, lexical change, and typological/morphosyntactic change. Here, important aspects include the inherent propensity of change, the role of arbitrariness, the role of systems, horizontal transfer, and the outcome of change at macro-levels. Finally, the chapter deals with the issue of the ontological status of the reconstruction, and how various theoretical approaches may affect the interpretation of results. The chapter reviews results and controversies arising from current research.