Language evolves. Its development in the human animal, in its behavioural, mental and physiological aspects, is a story yet to be fully told; it will not be essayed here. But once language has established itself as the characteristic medium of interaction in the species-and even in its earliest observable forms has achieved an astonishing richness of systems and delicacy of communicative function-then any one manifestation of it splits into different versions and the shape of its elements changes even among a heredity of users. The study known as ‘historical-comparative linguistics’ (or some similar title according to the researcher’s school and language) attempts to trace those splits and detail those changes. Of necessity, it also seeks to establish just what array of forms, at what time, is the datum from which the splits diverge and the changes move. In what follows historical comparativism will be considered in respect of its own history, its methods, its dynamics and its areas of contention.