(parent language, or Ursprache), a term designating a hypothetical state of a group or family of related languages, reconstructed on the basis of a system of correspondences established between the languages in phonetics, grammar, and semantics by the comparative historical method—for example, Proto-Indo-European and Proto-Slavic.
The reality of a protolanguage as a unified spoken language of a specific prehistorical ethnos remains controversial. A protolanguage may also be understood as a group of closely related dialects, from which more recent groups of historically attested languages arose as a result of individual development. If the origin and development of a group of related languages do not predate recorded history, the reality of a protolanguage may be strictly documented—for instance, the modern Romance languages, whose protolanguage was the Latin vernacular known as Vulgar Latin. The elements and forms of a protolanguage are called archetypes. Their correspondences at subsequent stages of linguistic evolution are called reflexes.
V. A. VINOGRADOV