Published online by Cambridge University Press: 14 July 2016
A model is given to describe the concurrent evolution of vocabularies of different languages belonging to the same family. Lexical change involves the replacement of old words by new words acquired by inheritance, borrowing or some other form of innovation. This process is described by a set of simultaneous differential equations involving the probabilities that, at any time, languages share similar words for any particular meaning. Various special cases of the model are compared using data for some Indo-European languages.