chapter  1
Language Isolates and their History
ByLyle Campbell
Pages 18

The standard definition is that a language isolate is a language that has no known relatives, that is, that has no demonstrable phylogenetic relationship with any other language. A language family is a set of languages for which there is sufficient evidence to show that they descend from a single common ancestral language and are therefore phylogenetically related to one another. Some languages which were once thought to be isolates have proven to be members of small families of related languages. This illustrates a second way in which language isolates and language families are not so different from one another. An unclassified language is one for which there is not enough data to determine whether it has relatives - for these languages, there is insufficient data to compare them meaningfully with other languages, and therefore any possible kinship they may have remains unknown.