The Proto-Greek language is the assumed last common ancestor of all known varieties of Greek, including Mycenaean, the classical Greek dialects (Attic-Ionic, Aeolic, Doric and Arcado-Cypriot), and ultimately Koine, Byzantine and modern Greek. Some scholars would include the fragmentary ancient Macedonian language, either as descended from an earlier "Proto-Hellenic" language, or by definition including it among the descendants of Proto-Greek as a Hellenic language and/or a Greek dialect. Proto-Greek would already have been spoken in the Late Neolithic period, most probably in the Balkans (i.e. northwestern Greece).
Four dialect groups have evolved from Proto-Greek:
- Proto-Ionic, mother of Attic? and Ionic?.
- Proto-Achaeic, spoken by the Achaeans, who were the main bearers of the Mycenaean culture (ca. 1600-1200). Mycenaean? language is the most ancient attested Greek.
- Proto-West Greek or Proto-Doric
An isogloss between Greek and Phrygian is the absence of r-endings in the Middle Voice in Greek, apparently already lost in Proto-Greek.
Proto-Greek inherited the augment, a prefix é- to verbal forms expressing past tense. This feature it shares only with Indo-Iranian and Phrygian (and to some extent, Armenian), lending some support to a "Graeco-Aryan" or "Inner PIE" proto-dialect. However, the augment down to the time of Homer remained optional, and was probably little more than a free sentence particle meaning "previously" in the proto-language, that may easily have been lost by most other branches.
The first person middle verbal desinences -mai, -mān replace -ai, -a. The third singular pherei is an innovation by analogy, replacing the expected Doric *phereti, Ionic *pheresi (from PIE *bʱéreti).
The future tense is created, including a future passive, as well as an aorist passive.
The suffix 'ka' is attached to some perfects and aorists.
Infinitives in -ehen, -enai and -men are created.