Many societies in pre-1800 Africa depended on orality both for communication and for record keeping. Historians of Africa, among other ways of dealing with this issue, treat languages as archives and apply what is sometimes called the “words and things” approach. Every language is an archive, in the sense that its words and their meanings have histories. The presence and use of particular words in the vocabulary of the language can often be traced back many centuries into the past. They are, in other words, historical artifacts. Their presence in the language in the past and their meanings in those earlier times tell us about the things that people knew, made use of, and talked about in past ages. They provide us complex insights into the world in which people of past societies lived and operated.
But in order to reconstruct word histories, historians first need to determine the relationships and evolution of the languages that possessed those words. The techniques of comparative historical linguistics and language classification allow one to establish a linguistic stratigraphy: to show how the periods can be established in which meaning changes in existing words or changes in the words used for particular meanings took place, to assess what these word histories reveal about changes in a society and its culture, and to identify whether internal innovation or encounters with other societies mediated such changes.
The comparative method on its own cannot establish absolute dates of language divergence. The method does allow scholars, however, to reconstruct the lexicons of material culture used at each earlier period in the language family tree. These data identify the particular cultural features to look for in the archaeology of people who spoke languages of the family in earlier times, and that evidence in turn enables scholars to propose datable archaeological correlations for the nodes of the family tree. A second approach to dating a language family tree has been a lexicostatistical technique, often called glottochronology, which seeks to estimate how long ago sister languages began to diverge out of their common ancestor language by using calculations based on the proportion of words in the most basic parts of the vocabulary that the languages still retain in common. Recent work in computational linguistic phylogenetics makes use of elements of lexicostatistics, and there have been efforts to automate the comparative method as well.
In order to compare languages historically, two important issues first have to be confronted, namely data acquisition and data analysis. Linguistic field collection of vocabularies from native speakers and linguistic archive work, especially with dictionaries, are principal means of data acquisition. The comparative historical linguistic approach and methods provide the tools for analyzing these linguistic data, both diachronically and synchronically.
Nearly all African languages have been classified into four language families, namely: Niger-Congo, Nilo-Saharan, Afroasiatic, and Khoisan. The Malagasy language of Madagascar is an exception, in that it was brought west across the Indian Ocean to that island from the East Indies early in the first millennium ce. Malagasy as well as several languages with an Indo-European origin, such as Afrikaans, Krio, and Nigerian Pidgin English, are not part of this discussion.
The classification of the Transeurasian languages
