For the beginning or general student, dialectology and the history of the English language can both be taught with a common frame of reference provided by certain principles of linguistic change. Related in obvious ways with the history of language but often overlooked in dialectology, these principles are (1) that any living language is certain to be changed by its speakers, (2) that speakers who use a language together change it similarly, (3) that different languages become more alike as their speakers communicate with one another, and (4) that speakers who use a language separately change it differently. For instance, because the speakers of Indo-European separated into groups isolated from one another, the natural changes which occurred in the language differed from group to group until the resultant languages became mutually unintelligible. Similarly, dialect differences now common in the United States have occurred because of the isolation of various groups in the culture and can be explained in terms of linguistic change. Dialects, which are now maintained because a child learns the dialect of his acquaintances, will converge when the various groups in the culture interact with one another. (JS)