Languages change through time, and historical linguistics is the branch of linguistics that provides a systematic study of this phenomenon. The study of change taking place in a particular language requires reference both to the structural properties of that language and to the social environment in which it functions: Which social groups initiate and propagate particular changes? Which social circumstances lead to language change, such as creation of new vocabulary or shifts in meaning? How do languages change as a result of contact with other languages? Some languages are related through descent from a common ancestor, as English and German descend from Proto-Germanic, and these languages plus Spanish and Russian descend in turn from proto-Indo-European. What are the criteria that enable us to decide that two languages are genealogically (genetically) related in this way, especially given that similarities between languages can also arise through contact? Assuming that we can establish genealogical relations among languages, to what extent can we reconstruct their common ancestor? For instance, how can we reconstruct the structure of Proto-Indo-European and perhaps even some aspects of the culture in which it was spoken? Such considerations lead further to interdisciplinary cooperation with archaeology (the physical record), anthropology (the cultural environment), and population genetics (biological inheritance).
Bernard Comrie, Marianne Mithun
Linguistics 215: Introduction to Historical-Comparative Linguistics
Linguistics 223: Languages in Contact
Linguistics 236: Advanced Language Change
Linguistics 255A-B: Seminar in Language Change