The evolution or historical development of language is made up of diverse facts and processes. In the first place it includes the internal or structural development of the language system, its various subsystems 14 and component parts. The description of internal linguistic history is usually presented in accordance with the division of language into linguistic levels. The main, commonly accepted levels are: the phonetic and phonological levels, the morphological level, the syntactic level, and the lexical level. Accordingly, the history of the language can be subdivided into historical phonetics (phonology), historical morphology, historical syntax and historical lexicology.
The evolution of language includes also many facts which pertain to the functioning of language in the speech community. These functional aspects constitute what is known as the "external" history of the language and embrace a large number of diverse matters: the spread of the language in geographical and social space, the differentiation of language into functional varieties (geographical variants, dialects, standard and substandard forms, etc.), contacts with other languages. In discussing these aspects of history we shall deal with the concept of language space, that is the geographical and social space occupied by the language (known as its horizontal and vertical dimensions); and also with the concept of linguistic situation, which embraces the functional differentiation of language and the relationships between the functional varieties. Most of these features are connected with the history of the speech community, e.g. with the structure of society, the migration of tribes, economic and political events, the growth of culture and literature.
