What is "language isolate"

n. A natural language with no proven genetic relationship to another language.

A language isolate, in the absolute sense, is a natural language with no demonstrable genealogical (or "genetic") relationship with other languages, one that has not been demonstrated to descend from an ancestor common with any other language. Language isolates are in effect language families consisting of a single language. Commonly cited examples include Ainu, Basque, Korean and Sumerian, though in each case a minority of linguists claim to have demonstrated a relationship with other languages.

Some sources use the term "language isolate" to indicate a branch of a larger family with only one surviving daughter. For instance, Albanian, Armenian and Greek are commonly called Indo-European isolates. While part of the Indo-European family, they do not belong to any established branch (like the Romance, Indo-Iranian, Slavic or Germanic branches), but instead form independent branches of their own. Similarly, within the Romance languages, Sardinian is a relative isolate. However, without a qualifier, isolate is understood to be in the absolute sense of having no demonstrable genetic relationship to any other known language.

Some languages once seen as isolates may be reclassified as small families. This happened with Japanese (now included in the Japonic family along with Ryukyuan languages such as Okinawan) and Georgian (now the most dominant or standard of the Kartvelian languages). The Etruscan language of Italy has long been considered an isolate, but some have proposed that it is related to the so-called Tyrsenian languages, an extinct family of closely related ancient languages proposed by Helmut Rix (1998), which includes the Raetic language of the Alps and the Lemnian language of the Aegean Sea. The Japonic and Kartvelian families are widely accepted by linguists, but since the ancient family that includes Etruscan has not yet received a similar level of acceptance, Etruscan is still included in the list of language isolates.

Language isolates may be seen as a special case of unclassified languages that remain unclassified even after extensive efforts. If such efforts eventually do prove fruitful, a language previously considered an isolate may no longer be considered one, as happened with the Yanyuwa language of northern Australia, which has been placed in the Pama–Nyungan family. Since linguists do not always agree on whether a genetic relationship has been demonstrated, it is often disputed whether a language is an isolate or not.