Language isolate

A language isolate, in the absolute sense, is a 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 consisting of a single language. Commonly cited examples include, , , , , and , 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 member. For instance,, and  are commonly called Indo-European isolates. While part of the, they do not belong to any established branch (such as the , , , or  branches), but instead form independent branches. Similarly, within the Romance languages, is a relative isolate. However, without a qualifier, isolate is understood to mean 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 (now included in the  along with  such as ). The of Italy has long been considered an isolate, but some have proposed that it is related to the so-called, an extinct family of closely related ancient languages proposed by  in 1998, including the , formerly spoken in the central , and the , formerly spoken on the Greek island of.

Language isolates may be seen as a special case of s 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 of northern, which has been placed in the  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.

"Genetic" or "genealogical" relationships
The term "genetic relationship" is meant in the genealogical sense of, which groups most languages spoken in the world today into a relatively small number of , according to reconstructed descent from common ancestral languages. A "genetic relationship" is a connection between languages, like similarities in vocabulary or grammar, that can be attributed to a common ancestral proto-language that diverged into multiple languages or branches. For example, is related to other  and  is related to other. By this criterion, each language isolate constitutes a family of its own, which explains the exceptional interest that these languages have received from linguists.

Looking for relationships
It is possible that all s spoken in the world today are related by direct or indirect descent from a single ancestral tongue. The established language families would then be only the upper branches of the genealogical tree of all languages, or, equally, lower progeny of a parent tongue. For this reason, language isolates have been the object of numerous studies seeking to uncover their genealogy. For instance, has been compared with every living and extinct Eurasian language family known, from  to, without conclusive results.

In some situations, a language with no ancestor can arise. This frequently happens with s—most famously in the case of, where deaf children with no language were placed together and developed a new language. Similarly, if deaf parents were to raise a group of hearing children who have no contact with others until adulthood, they might develop an oral and keep using it later, teaching it to their children, and so on. Eventually, it could develop into the full-fledged language of a population. With unsigned languages, this is not very likely to occur at any one time but, over the tens of thousands of years of human prehistory, the likelihood of this occurring at least a few times increases. There are also s and s such as, which do not descend directly from a single ancestor but have become the language of a population; however, they do take elements from existing languages.

Extinct isolates
Caution is required when speaking of s as isolates. Despite their great age, and  can be safely classified as isolates, as the languages are well enough known that, if modern relatives existed, they would be recognizably related.

However, many extinct languages are very poorly attested, and the fact that they cannot be linked to other languages may be a reflection of our poor knowledge of them. ,, and are also believed to be isolates by mainstream majority, but their status is disputed by a minority of linguists. Many extinct languages of the such as  and  may likewise have been isolates. A language thought to be an isolate may turn out to be relatable to other languages once enough material is recovered, but material is unlikely to be recovered if a language was not documented in writing.

Sign language isolates
A number of s have arisen independently, without any ancestral language, and thus are true language isolates. The most famous of these is the, a well documented case of what has happened in schools for the deaf in many countries. In Tanzania, for example, there are seven schools for the deaf, each with its own with no known connection to any other language. Sign languages have also developed outside schools, in communities with high incidences of deafness, such as in Bali, the  in Ghana, the  in Brazil, several, and half a dozen sign languages of the hill tribes in Thailand including the.

Studies are also being conducted on (ABSL) in an isolated village in Israel. The language was developed in isolation for over 75 years by both deaf and hearing people within the village.

These and more are all presumed isolates or small local families, because many deaf communities are made up of people whose hearing parents do not use sign language, and have manifestly, as shown by the language itself, not borrowed their sign language from other deaf communities during the recorded history of these languages.

List of language isolates by continent
Below is a list of known language isolates, arranged by continent, along with notes on possible relations to other languages or language families.

The Status column indicates the long-term viability of the language, according to the definitions of the UNESCO Atlas of the World's Languages in Danger. "Vibrant" languages are those in full use by speakers of every generation, with consistent native acquisition by children. "Vulnerable" languages have a similarly wide base of native speakers, but a restricted use and the long-term risk of. "Endangered" languages are either acquired irregularly or only spoken by older generations. "Moribund" languages have only a few remaining native speakers, with no new acquisition, highly restricted use, and near-universal bilingualism. "Extinct" languages have no native speakers, but are sufficiently documented to be classified as isolates.

Africa
With few exceptions, all of Africa's languages have been gathered into four major phyla:, , and. However, the genetic unity of some language families, like and, is questionable, and so there may be many more language families and isolates than currently accepted. Data for several African languages, like and, are not sufficient for classification. In addition,, , , , and a few other languages within and -speaking areas may turn out to be isolates upon further investigation. and are highly divergent languages located within -speaking areas, and may also possibly be language isolates.

Oceania
The of  are poorly studied, and candidates for isolate status are likely to change when more becomes known about them.