Variation and change are facts of every language. There are many reasons for variation: geographic isolation causes people who live in different regions to speak different varieties of a language; sociocultural isolation results in different groups of people, defined by ethnicity, vocation, social class, age, gender, and many other variables, speaking different varieties. People who speak different languages interact with each other and “borrow” sounds, words, and grammatical features from one another, thus changing their languages by the addition of these borrowed features. New functions appear every day in the form of new situations, concepts, and perspectives that speakers wish to express. Also, some forms and functions become archaic, and gradually cease to be employed in the language of everyday life. Styles and mannerisms simply change. These and many other factors lead to variation in the form of language, even in the speech of a single individual. Across time and space, this variation results in the splintering of a language into different varieties, and eventually distinct “daughter” languages. This process is the topic of historical and comparative linguistics.

Often change is equated with deterioration, as though at some early stage the language exists in an ideal state, and as subsequent generations of speakers introduce changes, the language successively degenerates. In the English tradition, we revere the language of Shakespeare, or the King James Bible, and deplore the “sloppy” or “illogical” ways in which younger people speak.