Graeco-Armenian (or Helleno-Armenian) is the hypothetical common ancestor of Greek and Armenian that postdates Proto-Indo-European. Its status is comparable to that of the Italo-Celtic grouping: each is widely considered plausible without being accepted as established communis opinio. The hypothetical Proto-Graeco-Armenian stage would need to date to the 3rd millennium BC and would be only barely different from either late Proto-Indo-European or Graeco-Armeno-Aryan.
The Graeco-Armenian hypothesis originated in 1924 with Holger Pedersen, who noted that agreements between Armenian and Greek lexical cognates are more common than between Armenian and any other Indo-European language.
During the mid-to-late 1920s, Antoine Meillet further investigated morphological and phonological agreements and postulated that the parent languages of Greek and Armenian were dialects in immediate geographical proximity to their patent language, Proto-Indo-European. Meillet's hypothesis became popular in the wake of his Esquisse d'une grammaire comparée de l'arménien classique.
G. R. Solta does not go as far as postulating a Proto-Graeco-Armenian stage but concludes that the lexicon and the morphology clearly make Greek the language that is the most closely related to Armenian.
Eric Hamp supports the Graeco-Armenian thesis and even anticipates a time that "we should speak of Helleno-Armenian" (the postulate of a Graeco-Armenian proto-language). James Clackson is more reserved, considers the evidence of a Graeco-Armenian subgroup to be inconclusive and believes Armenian to be in a larger Graeco-Armeno-Aryan family.
Evaluation of the hypothesis is tied up with the analysis of the poorly attested Phrygian language. While Greek is attested from very early times, allowing a secure reconstruction of a Proto-Greek language dating to about the 3rd millennium BC, the history of Armenian is opaque where its earliest testimony is the 5th-century Bible translation of Mesrob Mashtots. Armenian has many loanwords showing traces of long language contact with Greek and Indo-Iranian languages; in particular, it is a satem language. Also, Armenian and Greek share a voiceless aspirate series.
Luay Nakhleh, Tandy Warnow, Don Ringe, and Steven N. Evans compared various phylogeny methods and found that five procedures (maximum parsimony, weighted and unweighted maximum compatibility, neighbor joining, and the widely-criticized technique of Russell Gray and Quentin D. Atkinson) support a Graeco-Armenian subgroup.
An interrelated problem is whether there is a "Balkan Indo-European" subgroup of Indo-European, of not only Greek and Armenian but also Albanian and possibly some dead languages in the Balkans. That has been argued for in various publications by scholars such as G. Neumann, G. Klingenschmitt, J. Matzinger, J. H. Holst. The Balkan subgroup, in turn, is supported by the lexico-statistical method of Hans J. Holm.
- Clackson, James (1995). The Linguistic Relationship Between Armenian and Greek. Oxford: Wiley-Blackwell. ISBN 9780631191971.
- Georgiev, Vladimir Ivanov (1981). Introduction to the History of the Indo-European Languages. Sofia: Bulgarian Academy of Sciences.
- Gray, Russell D.; Atkinson, Quentin D. (2003). "Language-tree Divergence Times Support the Anatolian Theory of Indo-European Origin". Nature. 426 (6965): 435–439. doi:10.1038/nature02029. PMID 14647380.
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- Hamp, Eric (1976). "*gweiH- "live"". In Davies, Anna Morpurgo; Meid, Wolfgang. Studies in Greek, Italic and Indo-European Linguistics offered to Leonhard R. Palmer. Innsbruck: University of Innsbruck. pp. 87–91.
- Holm, Hans J. (2008). "The Distribution of Data in Word Lists and its Impact on the Subgrouping of Languages". In Preisach, Christine; Burkhardt, Hans; Schmidt-Thieme, Lars; Decker, Reinhold. Data Analysis, Machine Learning, and Applications. Proceedings of the 31st Annual Conference of the Gesellschaft für Klassifikation e.V., Albert-Ludwigs-Universität Freiburg, March 7–9, 2007. Berlin-Heidelberg: Springer-Verlag. pp. 628–636. ISBN 9783540782469.
- Holst, Jan Henrik (2009). Armenische Studien (in German). Wiesbaden: Harrassowitz Verlag. ISBN 9783447061179.
- Meillet, Antoine (1925). "Remarques sur l'étymologie de quelques mots grecs". Bulletin de la société de linguistique de Paris (in French). 26: 1–6.
- Meillet, Antoine (1927). "De la prothèse vocalique en grec et en arménien". Bulletin de la société de linguistique de Paris (in French). 27: 129–135.
- Meillet, Antoine (1903). Esquisse d'une grammaire comparée de l'arménien classique (in French). Vienna: Imprimerie des PP. Mékhitharistes.
- Nakhleh, Luay; Warnow, Tandy; Ringe, Don; Evans, Steven N. (2005). "A Comparison of Phylogenetic Reconstruction Methods on an Indo-European Dataset" (PDF). Transactions of the Philological Society. 3 (2): 171–192.
- Pedersen, Holger (1924). "Armenier Sprache". In Ebert, Max. Reallexikon der Vorgeschichte (in German). 1. Berlin: Walter de Gruyter. pp. 219–226.
- Schmitt, R. (1972). "Die Erforschung des Klassisch-Armenischen seit Meillet (1936)". Kratylos (in German). 17: 1–68.
- Solta, G. R. (1960). Die Stellung des Armenischen im Kreise der Indogermanischen Sprachen (in German). Vienna: Mechitharisten-Buchdruck.