Most languages are known to belong to language families ("families" hereforth). An accurately identified family is a phylogenetic unit, i.e., all its members derive from a common ancestor. The ancestor is very seldom known to us directly, since most languages have a very short recorded history. However, it is possible to recover many of the features of the common ancestor of related languages by applying the comparative method -- a reconstructive procedure worked out by 19th-centurylinguistAugust Schleicher. It can demonstrate the family status of many of the groupings listed below.
Language families can be subdivided into smaller units, conventionally referred to as "branches" (because the history of a language family is often represented as a "tree" diagram).
The common ancestor of a family (or branch) is known as its "protolanguage". For example, the reconstructible protolanguage of the well-known Indo-European family is called Proto-Indo-European (not known from written records, since it was spoken before the invention of writing). Sometimes a protolanguage can be identified with a historically known language. Thus, provincial dialects of Latin ("Vulgar Latin") gave rise to the modern Romance languages, so the Proto-Romance language is more or less identical with Latin (if not exactly with the literary Latin of the Classical writers), and dialects of Old Norse are the protolanguage to Norwegian, Swedish, Danish and Icelandic.
Languages that cannot be reliably classified into any family are known as language isolates.
In the following, each "bulleted" item is a known language family. The geographic headings over them are meant solely as a tool for grouping families into collections more comprehensible than an unstructured list of the dozen or two of independent families. Geographic relationship is convenient for that purpose, but these headings are not a suggestion of any "super-families" phylogenetically relating the families named.
Ainu language or languages (Russia, Japan) (like Arabic or Japanese, the diversity within Ainu is large enough that some consider it to be perhaps up to a dozen languages while others consider it a single language with high dialectal diversity)
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