text: In the tree model of historical linguistics, a proto-language is a postulated ancestral language from which a number of attested languages are believed to have descended by evolution, forming a language family. Proto-languages are usually unattested, or partially attested at best. They are reconstructed by way of the comparative method.
  In the family tree metaphor, a proto-language can be called a mother language. Occasionally, the German term Ursprache (from Ur- "primordial, original", and Sprache "language", ) is used instead. It is also sometimes called the common or primitive form of a language (e.g. Common Germanic, Primitive Norse).
  In the strict sense, a proto-language is the most recent common ancestor of a language family, immediately before the family started to diverge into the attested daughter languages. It is therefore equivalent with the ancestral language or parental language of a language family.
  Moreover, a group of languages (such as a dialect cluster) which are not considered separate languages (for whichever reasons) may also be described as descending from a unitary proto-language.
  Definition and verification
  Typically, the proto-language is not known directly. It is by definition a linguistic reconstruction formulated by applying the comparative method to a group of languages featuring similar characteristics. The tree is a statement of similarity and a hypothesis that the similarity results from descent from a common language.