It has long been recognised that a living language can never be absolutely static; it develops together with the speech community, that is, with the people who speak it.
The great upsurge of interest in historical linguistics and its actual rise from the state of amateur speculation to a serious science date from the early 19th c. Accumulation of facts about the early stages of living languages called for theoretical interpretation of linguistic evolution. It was soon realised that the relationship of language to time involved many difficult and contradictory problems. Here are some of the questions which may naturally arise in connection with language history: What does the evolution of language consist of? Is the concept "evolution" equivalent to that of "linguistic change"? How does a linguistic change operate? What are the conditions or factors that determine and direct the development of language? What are the relationships between the facts of internal linguistic history and the history of the people?
In order to answer such questions with regard to English, and to understand not only what events occurred in the course of time but also how and why they occurred we must first consider a few theoretical questions and principles pertaining to language history.
