Graeco-Armenian (also Helleno-Armenian) is the hypothetical common ancestor of the Greek and Armenian languages that postdates the Proto-Indo-European language (PIE). 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, only barely differentiated from either late PIE or Graeco-Armeno-Aryan.
The Graeco-Armenian hypothesis originated in 1924 with Holger Pedersen, who noted that the number of Greek-Armenian lexical cognates is greater than that of agreements between Armenian and any other Indo-European language. During the mid-to-late 1920s, Antoine Meillet further investigated morphological and phonological agreements, postulating that the parent languages of Greek and Armenian were dialects in immediate geographical proximity in the parent language. 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 he concludes that considering both the lexicon and morphology, Greek is clearly the dialect most closely related to Armenian. Eric Hamp supports the Graeco-Armenian thesis, anticipating even a time "when we should speak of Helleno-Armenian" (meaning the postulate of a Graeco-Armenian proto-language). James Clackson is again more reserved, holding the evidence in favour of a positive Graeco-Armenian sub-group to be inconclusive and tends to include Armenian into 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 circa 3rd millennium BC, the history of Armenian is opaque. It is strongly linked with Indo-Iranian languages; in particular, it is a satem language.
The earliest testimony of the Armenian language dates to the 5th century AD (the Bible translation of Mesrob Mashtots). The earlier history of the language is unclear and the subject of much speculation. It is clear that Armenian is an Indo-European language, but its development is opaque. In any case, Armenian has many layers of loanwords and shows traces of long language contact with Greek and Indo-Iranian. 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, which would comprise not only Greek and Armenian, but also Albanian and possibly some dead languages on the Balkans. This theory has been argued for in various publications by scholars such as G. Neumann, G. Klingenschmitt, J. Matzinger, J. H. Holst. This 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. PMID 14647380. doi:10.1038/nature02029.
- 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.