Protolanguage

A proto-language in the tree model of historical linguistics is a language, usually hypothetical or reconstructed, and unattested, from which a number of attested, or documented, known languages are believed to have descended by evolution, or slow modification of the proto-language into languages that form a language family.

In the strict sense, a proto-language is the latest common ancestor of a language family, immediately before the start of the family's divergence into the attested daughter languages. It is therefore equivalent with the ancestral language or parental language of a language family.

Moreover, a group of idioms (such as a dialect cluster) which are not considered separate languages (for whichever reasons) can also be described as descending from a unitary proto-language.

Occasionally, the German term Ursprache (from Ur- "primordial" and Sprache "language", pronounced [ˈʔuːɐ.ʃpʁaː.xə]) is used instead.

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.

The comparative method, a process of deduction, begins from a set of characteristics, or characters, found in the attested languages. If the entire set can be accounted for by descent from the proto-language, which must contain the proto-forms of them all, the tree, or phylogeny, is regarded as a complete explanation and by Occam's razor, is given credibility. More recently such a tree has been termed "perfect" and the characters labelled "compatible."

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