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. The unity of Proto-Greek would have ended as Hellenic migrants, speaking the predecessor of the Mycenaean language, entered the Greek peninsula either during the Neolithic period or the Bronze Age.
The evolution of Proto-Greek should be considered within the context of an early Paleo-Balkan sprachbund that makes it difficult to delineate exact boundaries between individual languages. The characteristically Greek representation of word-initial laryngeals by prothetic vowels is shared by the Armenian language, which also shares other phonological and morphological peculiarities of Greek. The close relatedness of Armenian and Greek sheds light on the paraphyletic nature of the Centum-Satem isogloss. The close similarities between Ancient Greek and Vedic Sanskrit suggest that both Proto-Greek and Proto-Indo-Iranian were still quite similar to either late Proto-Indo-European, which would place the latter somewhere in the late 4th millennium BC.
Scholars are divergent in their views regarding the geographical origins of proto-Greek and when the first Greek-speakers arrived into the Greek peninsula. Vladimir I. Georgiev, for example, placed proto-Greek in northwestern Greece during the Late Neolithic period. Eric Hamp, however, placed the first speakers of Greek and ancient Macedonian ("Helleno-Macedonian") in the northeast coast of the Black Sea and its hinterlands who migrated to Greece through Anatolia during the Bronze Age. In the field of archaeogenetics, Russel Gray and Quentin Atkinson, using computational methods derived from evolutionary biology, concluded that the divergence of Greco-Armenian from Proto-Indo-European occurred around 7300–7000 years ago (~5300–5000 BC) coinciding with the spread of agriculture from Asia Minor to Greece during the Neolithic period; Greek, specifically, developed into a separate linguistic lineage before 6000 years ago (before 4000 BC).
The primary sound changes separating Proto-Greek from the Proto-Indo-European language included:
- Debuccalization of /s/ to /h/ in the inter-and pre-vocalic positions (i.e. between two vowels, or if word-initial and followed by a vowel).
- De-voicing of voiced aspirates.
- Strengthening of word-initial y- (not Hy-) to dy- (later ζ-).
- Palatalization of consonants followed by -y-, producing various affricates (still represented as a separate sound in Mycenaean) and palatal consonants; these later simplified, mostly losing their palatal character.
- Dissimilation of aspirates (Grassmann's law), possibly post-Mycenaean.
- Vocalization of laryngeals between consonants and initially before consonants to /e/, /a/, /o/ from h₁, h₂, h₃ respectively (unlike all other Indo-European languages).
- Other unique changes involving laryngeals; see below.
- Loss of final stop consonants; final /m/ -> /n/.
- Cowgill's law, raising /o/ to /u/ between a resonant and a labial.
- Merging of sequences of velar + *w into the labiovelars, with compensatory lengthening of the consonant in some cases. For example PIE *h₁éḱwos > PG *íkkʷos > Mycenaean i-qo /ikkʷos/, Attic híppos, Aeolic íkkos.
Loss of prevocalic *s was not completed entirely, famously evidenced by sȳs (also hȳs, pig, from PIE *suh₁-), dasýs (dense) and dásos (dense growth, forest); syn (with) is another example, contaminated with PIE *kom (Latin cum, Proto-Greek *kon) to Homeric / Old Attic ksyn. Sélas (light in the sky, as in the "Northern Lights") and selēnē/selána (the Moon) may be more examples of the same, if actually derived from PIE *swel- (to burn) (possibly related to hēlios "Sun", Ionic hēelios < *sāwelios).
Dissimilation of aspirates (so-called Grassmann's law) caused an initial aspirated sound to lose its aspiration when a following aspirated consonant occurred in the same word. It was a relatively late change in Proto-Greek history and must have occurred independently of the similar dissimilation of aspirates (also known as Grassmann's law) in Indo-Iranian, although it may represent a common areal feature. Specifically:
- It postdates the Greek-specific de-voicing of voiced aspirates.
- It also postdates the change of /s/ > /h/, as it affects /h/ as well: ékhō "I have" < *hekh- < PIE *seǵʰ-oh₂, but future heksō "I will have" < *heks- < Post-PIE *seǵʰ-s-oh₂.
- It even postdates the loss of aspiration before /y/ that accompanied second-stage palatalization (see below), which postdates both of the previous changes (as well as first-stage palatalization).
- On the other hand, it predates the development of the first aorist passive marker -thē-, since the aspirate in that marker has no effect on preceding aspirates.
Greek is unique in reflecting the three different laryngeals using distinct vowels. Most Indo-European languages can be traced back to a dialectal variety of late Proto-Indo-European (PIE) where all three laryngeals had merged (after coloring adjacent short /e/ vowels) but Greek clearly cannot. For this reason, Greek is extremely important in reconstructing PIE forms.
Greek shows distinct reflexes of the laryngeals in various positions:
- Most famously, between consonants, where original vocalic h₁, h₂, h₃ are reflected as /e/, /a/, /o/ respectively (the so-called triple reflex). All other Indo-European languages reflect the same vowel from all three laryngeals (usually /a/, but /i/ or other vowels in Indo-Iranian). Examples:
|dʰh̥₁s- "sacred, religious"||thés-phatos "decreed by God"||dhíṣ-ṇya- "devout"||fānum "temple" < *fasnom < *dʰh̥₁s-no-|
|sth̥₂-to- "standing, being made to stand"||statós||sthíta-||status|
- An initial laryngeal before a consonant (an *HC- sequence) leads to the same triple reflex, whereas most IE languages deleted such laryngeals and a few reflect them initially before consonants, whereas Greek vocalized them (leading to what are misleadingly termed prothetic vowels): cf. Greek érebos "darkness" < PIE *h₁regʷos vs. Gothic riqiz- "darkness"; Greek áent- "wind" < *awent- < PIE *h₂wéh₁n̥t- vs. English wind, Latin ventum "wind".
- The sequence *CRHC (C = consonant, R = resonant, H = laryngeal) becomes CRēC, CRāC, CRōC from H = h₁, h₂, h₃ respectively. (Other Indo-European languages again have the same reflex for all three laryngeals, e.g. *CuRC in Germanic, *CíRC/CúRC with acute accent in Balto-Slavic, *CīRC/CūRC in Indo-Iranian, *CRāC in Italic and Celtic.) Sometimes CeReC, CaRaC, CoRoC is found instead. Cf. Greek thánatos "death" vs. Doric Greek thnātós "mortal", both apparently reflecting *dʰn̥h₂-tos. It is sometimes suggested that the position of the accent was a factor in determining the outcome.
- The sequence *CiHC tends to become *CyēC, CyāC, CyōC from H = h₁, h₂, h₃ respectively, with later palatalization (see below). Sometimes the outcome CīC is found, as in most other Indo-European languages, or the outcome CiaC in the case of *Cih₂C.
All of these cases may stem from an early insertion of /e/ next to a laryngeal not adjacent to a vowel in the Indo-European dialect ancestral to Greek (subsequently colored to /e/, /a/, /o/ by the particular laryngeal in question), prior to the general merger of laryngeals. For example:
- *CHC > *CHeC > CeC/CaC/CoC.
- *HC- > *HeC- > eC-/aC-/oC-.
- *CRHC > *CReHC > CRēC/CRāC/CRōC; or, *CRHC > *CeRHeC > *CeReC/CeRaC/CeRoC > CeReC/CaRaC/CoRoC by assimilation.
- *CiHC > *CyeHC > CyēC/CyāC/CyōC; or, *Cih₂C > *Cih₂eC > *CiHaC > *CiyaC > CiaC; or, *CiHC remains without vowel insertion > CīC.
A laryngeal adjacent to a vowel develops along the same lines as in other Indo-European languages:
- The sequence *CRHV (C = consonant, R = resonant, H = laryngeal, V = vowel) passes through *CR̥HV, becoming CaRV.
- The sequence *CeHC becomes CēC/CāC/CōC.
- The sequence *CoHC becomes CōC.
- In the sequence *CHV (including CHR̥C, with a vocalized resonant), the laryngeal colors a following short /e/, as expected, but otherwise disappears entirely (as in most other Indo-European languages, but contrast Indo-Iranian, where the laryngeal aspirates a previous stop and prevents the operation of Brugmann's law).
- In a *VHV sequence (i.e. a laryngeal between vowels, including a vocalic resonant R̥), the laryngeal again colors any adjacent short /e/ but otherwise vanishes early on. This change appears to be uniform across the Indo-European languages and was probably the first environment in which laryngeals were lost. If the first V was i, u or a vocalic resonant, a consonantal copy was apparently inserted in place of the laryngeal (e.g. *CiHV > *CiyV, *CuHV > *CuwV, *CR̥HV possibly > *CR̥RV, with R̥ always remaining as vocalic up until the dissolution of vocalic resonants in the various daughter languages). Otherwise, a hiatus resulted, which was resolved in various ways in the daughter languages, typically by converting i, u and vocalic resonants, when directly following a vowel, back into a consonant, and merging adjacent non-high vowels into a single long vowel.
Proto-Greek underwent palatalization of consonants before *y. This occurred in two separate stages. The first stage affected only dental consonants, while the second stage affected all consonants.
The first palatalization turned dentals + *y into alveolar afficates:
Alongside these changes, the inherited clusters *ts, *ds and *tʰs all merged into *ts.
In the second palatalization, all consonants were affected. It took place following the resolution of syllabic laryngeals and sonorants. The following table, based on Sihler, shows the developments.
|*sy > *hy||*yy|
|*wy||*ɥɥ > *yy|
In post-Proto-Greek times, the resulting palatal consonants and clusters were resolved in varying ways. Most notably, *ň and *ř were resolved into plain sonorants plus a palatal on-glide, which eventually turned the preceding vowel into a diphthong.
|Proto-Greek||Attic||Homeric||West Ionic||Other Ionic||Boeotian||Arcado-
|*ňň||in (but *uin > ūn)|
|*řř||ir (but *uir > ūr)|
|*yy||(ai, ei, oi, ui)|
In the time between the first and second palatalizations, new clusters *tsy and *dzy were formed by restoring a lost *y after the newly-formed *ts and *dz. This occurred only in morphologically transparent formations, by analogy with similar formations where *y was preceded by other consonants. In formations that were morphologically opaque and not understood as such by speakers of the time, this restoration did not take place and *ts and *dz remained. Hence, depending on the type of formation, the Pre-Greek sequences *ty, *tʰy and *dy have different outcomes in the later languages. In particular, medial *ty becomes Attic s in opaque formations, but tt in transparent formations.
Note that the outcome of PG medial *ts in Homeric Greek is s after a long vowel, and vacillation between s and ss after a short vowel: tátēsi dat. pl. "rug" < tátēt-, possí(n)/posí(n) dat. pl. "foot" < pod-.
Examples of initial *ts:
- PIE *tyegʷ- "avoid" > PG *tsegʷ- > Greek sébomai "worship, be respectful" (Ved. tyaj- "flee")
- PIE *dʰyeh₂- "notice" > PG *tsā- > Dor. sāma, Att. sêma "sign" (Ved. dhyā́- "thought, contemplation")
Examples of medial *ts (morphologically opaque forms, first palatalization only):
- PreG *totyos "as much" > PG *totsos > Att. tósos, Hom. tósos/tóssos (cf. Ved. táti, Lat. tot "so much/many")
- PIE *medʰyos "middle" > PG *metsos > Att. mésos, Hom. mésos/méssos, Boeot. mettos, other dial. mesos (cf. Ved. mádhya-, Lat. medius)
Examples of medial *ťť (morphologically opaque forms, first and second palatalization):
- PIE *h₁erh₁-t-yoh₂ "I row" > PG *ereťťō > Attic eréttō, usual non-Attic eréssō (cf. erétēs "oarsman")
- PIE *kret-yōs > PreG *kret-yōn "better" > PG *kreťťōn > Attic kreíttōn, usual non-Attic kréssōn (cf. kratús "strong" < PIE *kr̥tus)
Other Post-Proto-Greek changes
Sound changes between Proto-Greek and all early dialects, including Mycenaean, include:
- Remaining syllabic resonants *m̥ *n̥ *l̥ and *r̥ are resolved to vowels or combinations of a vowel and consonantal resonant. It appears that this process still occurred within Proto-Greek, and resulted in an epenthetic vowel of undetermined quality (denoted here as *ə). This vowel then usually developed into a, but also o in some cases. Thus:
- *m̥, *n̥ > *ə, but > *əm, *ən before a sonorant. *ə appears as o in Mycenaean after a labial, e.g. pe-mo (spermo) "seed" vs. usual spérma < *spérmn̥. Similarly, o often appears in Arcadian after a velar, e.g. deko "ten", hekoton "one hundred" vs. usual déka, hekatón < *déḱm̥, *sem-ḱm̥tóm.
- *l̥, *r̥ > *lə, *rə, but *əl, *ər before sonorants and analogously. *ə appears as o in Mycenean Greek, Aeolic Greek, and Cypro-Arcadian. Example: PIE *str̥-tos > usual stratos, Aeolic strotos "army"; post-PIE *ḱr̥di-eh₂ "heart" > Att. kardíā, Hom. kradíē, Pamphylian korzdia.
- Loss of s in consonant clusters, with compensatory lengthening of the preceding vowel (Attic, Ionic, Doric) or of the consonant (Aeolic): *esmi "I am" > ēmi, eimi or emmi.
- Creation of secondary s from clusters, ntja > nsa (this in turn followed by a change similar to the one described above, i.e. loss of the n with compensatory lengthening, e.g. apont-ja > apon-sa > apō-sa, "absent", fem.).
- Conversion of labiovelars to velars next to /u/.
- In southern dialects (including Mycenaean, but not Doric), -ti- > -si- (assibilation).
The following changes are apparently post-Mycenaean:
- Loss of /h/ (from original /s/), except initially, e.g. Doric nikaas "having conquered" < *nikahas < *nikasas.
- Loss of /j/, e.g. treis "three" < *treyes.
- Loss of /w/ in many dialects (later than loss of /h/ and /j/). Example: etos "year" from *wetos.
- Loss of labiovelars, which were converted (mostly) into labials, sometimes into dentals (or velars next to /u/, as a result of an earlier sound change). See below for details. This had not yet happened in Mycenaean, shown by the fact that a separate letter /q/ is used for these sounds.
- Contraction of adjacent vowels resulting from loss of /h/ and /j/ (and, to a lesser extent, from loss of /w/); more in Attic Greek than elsewhere.
- Rise of a distinctive circumflex accent, resulting from contraction and certain other changes.
- Limitation of the accent to the last three syllables, with various further restrictions.
- Loss of /n/ before /s/ (incompletely in Cretan Greek), with compensatory lengthening of the preceding vowel.
- Raising of ā to ē /ɛː/ in Attic and Ionic dialects (but not Doric). In Ionic, this change was general, but in Attic it did not occur after /i/, /e/ or /r/. (But note Attic korē "girl" < *korwā; loss of /w/ after /r/ had not occurred at that point in Attic.)
Note that /w/ and /j/, when following a vowel and not preceding a vowel, combined early on with the vowel to form a diphthong and were thus not lost.
The loss of /h/ and /w/ after a consonant were often accompanied by compensatory lengthening of a preceding vowel.
The development of labiovelars varies from dialect to dialect:
- Labiovelars next to /u/ had earlier been converted to plain velars. Cf. boukólos "herdsman" < *gʷou-kʷolos (cf. boûs "cow" < *gʷou-) vs. aipólos "goatherd" < *ai(g)-kʷolos (cf. aíks, gen. aigós "goat"); elakhús "small" < *h₁ln̥gʷʰ-ús vs. elaphrós "light" < *h₁ln̥gʷʰ-rós.
- In Attic and some other dialects (but not, e.g., Lesbian), labiovelars before some front vowels became dentals. In Attic, kʷ and kʷʰ became t and th, respectively, before /e/ and /i/, while gʷ became d before /e/ (but not /i/). Cf. theínō "I strike, kill" < *gʷʰen-yō vs. phónos "slaughter" < *gʷʰón-os; delphús "womb" < *gʷelbʰ- (Sanskrit garbha-) vs. bíos "life" < *gʷih₃wos (Gothic qius "alive"), tís "who?" < *kʷis (Latin quis).
- All remaining labiovelars became labials, original kʷ kʷʰ gʷ becoming p ph b respectively. This happened to all labiovelars in some dialects, e.g. Lesbian; in other dialects, e.g. Attic, it occurred to all labiovelars not converted into dentals. Many occurrences of dentals were later converted into labials by analogy with other forms; cf. bélos "missile", bélemnon "spear, dart" (dialectal delemnon) by analogy with bállō "I throw (a missile, etc.)", bolḗ "a blow with a missile".
- Note that original PIE labiovelars had still remained as such even before consonants, and hence became labials also in this position, whereas in many other Centum languages, such as Latin and most Germanic languages, the labiovelars lost their labialization before consonants. (Greek pemptos "fifth" < *penkʷtos; compare Old Latin quinctus.) This makes Greek of particular importance in reconstructing original labiovelars.
The results of vowel contraction were complex from dialect to dialect. Such contractions occur in the inflection of a number of different noun and verb classes and are among the most difficult aspects of Ancient Greek grammar. They were particularly important in the large class of contracted verbs, denominative verbs formed from nouns and adjectives ending in a vowel. (In fact, the reflex of contracted verbs in Modern Greek — i.e., the set of verbs derived from Ancient Greek contracted verbs—represents one of the two main classes of verbs in that language.)
As Mycenaean Greek shows, the PIE dative (suffix -i), instrumental (suffix -phi) and locative (suffix -si) cases are still distinct, and are not yet syncretized into a single dative case.
Nominative plural -oi, -ai replaces late PIE -ōs, -ās.
The superlative in -tatos becomes productive.
The pronouns houtos, ekeinos and autos are created. Use of ho, hā, ton as articles is post-Mycenaean.
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 *bʰéreti).
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.
- "one": nominative *hens, genitive *hemos; feminine *mʰiā (> Myc. e-me /hemei/ (dative); Att./Ion. εἷς (ἑνός), μία, heis (henos), mia).
- "two": *duwō (> Myc. du-wo /duwō/; Hom. δύω, dyō; Att.-Ion. δύο, dyo)
- "three": nominative *trees, accusative trins (> Myc. ti-ri /trins/; Att./Ion. τρεῖς, treis; Lesb. τρής, trēs; Cret. τρέες, trees)
- "four": nominative *kʷetwores, genitive *kʷeturōn (> Myc. qe-to-ro-we /kʷetrōwes/ "four-eared"; Att. τέτταρες, tettares; Ion. τέσσερες, tesseres; Boeot. πέτταρες, pettares; Thess. πίτταρες, pittares; Lesb. πίσυρες, pisyres; Dor. τέτορες, tetores)
- "five": *penkʷe (> Att.-Ion. πέντε, pente; Lesb., Thess. πέμπε, pempe)
- "seven": *hepta
- "eight": *oktō
- "nine": *ennewa
- "ten": *deka
Eduard Schwyzer in his Griechische Grammatik has translated famous lines of Classical Greek into Proto-Greek. His reconstruction was ignorant of Mycenaean and assumes Proto-Greek loss of labiovelars and syllabic resonants, among other things. Thus, Schwyzer's reconstruction corresponds to an archaic but post-Mycenaean dialect rather than actual Proto-Greek.
|Original text||Proto-Greek reconstruction|
|Homer. Odyssey, 1.1.
(Ionia, 8th century BC)
|Ἄνδρα μοι ἔννεπε, Μοῦσα, πολύτροπον||ανερα μοι ενσεπε (or -τε), μοντja (μωντjα?), πολύτροπον||*anerã moi enʰekʷet, montˢa, polutrokʷon|
(Athens, early 4th century BC)
|ὅτι μὲν ὑμεῖς, ὦ ἄνδρες Ἀθηναῖοι, πεπόνθατε ὑπὸ τῶν ἐμῶν κατηγόρων, οὐκ οἶδα· ἐγὼ δ’ οὖν καὶ αὐτὸς ὑπ’ αὐτῶν ὀλίγου ἐμαυτοῦ ἐπελαθόμην, οὕτω πιθανῶς ἔλεγον. καίτοι ἀληθές γε ὡς ἔπος εἰπεῖν οὐδὲν εἰρήκασιν||῾ϝοττι μᾱν (?) υμμε, ω ανερες Αθᾱναιοι, πεπᾱσθε υπο κατᾱγορων μεο, ου ϝοιδα· εγω δε εον (?) κ. α. υ. α. ολιγοιο εμεο αυτοιο επελαθομᾱν, τως (or *τω) πιθανως (or -ω) ελεγοντ. κ. αλᾱθες γε ὡς (or ὡ) ϝεπος ϝειπεεν (or ϝευπ.) ουδε ἑν ϝεϝρηκᾰτι||*çokʷid mān umʰe. ō aneres Atʰānaïoi, pepãstʰe upo katāgorōn meho. oju woida; egō de ōn kai autos up’ autōn oligoço emeho autoço epi latʰomān, tō pitʰanō elegont. kai toi ãlātʰes ge çō wekʷos wewekʷehen oude hen wewrēkãti|
|The Lord's Prayer, Matthew 6:9
(Syria, late 1st century AD)
|πάτερ ἡμῶν ὁ ἐν τοῖς οὐρανοῖς, ἁγιασθήτω τὸ ὄνομά σου||πατερ αμμεων ὁ (τοισι) ορϝανοισι (resp. singular) (ἁγιον or αγνον εστωδ) ενυμα τϝεο||*pater ãmʰōn ho worʱanoihi, çagion estōd enumã tweho|
Notes: The reconstruction assumes that the old combinations of sonorants + s in either sequence (*ns, *ms, *rs, *ls, *u̯s, *i̯s, *sn, *sm, *sr, *sl, *su̯, *si̯ ) were pronounced as unvoiced sonorants ([n̥, m̥, r̥, l̥, ʍ, ç]) before they were simplified as short voiced sonorants with compensatory lengthening ν, μ, ρ, λ, (ϝ), (ι) in most dialects or as long voiced sonorants νν, μμ, ρρ, λλ, υ(ϝ), ι in Aeolic. It is also assumed that the PIE syllabic nasals (*n̥, *m̥) were pronounced as nasal [ã], before it split into α in most dialects and ο as a variant in some dialects (Mycenaean, Arcadian, Aeolic).
- Ancient Macedonian language
- Paleo-Balkan languages
- Pre-Greek substrate
- Proto-Indo-European language
- "MultiTree: A Digital Library of Language Relationships (Indo-European)". Ypsilanti, MI: Institute for Language Information and Technology.
- Georgiev 1981, p. 192: "Late Neolithic Period: in northwestern Greece the Proto-Greek language had already been formed: this is the original home of the Greeks."
- Hamp 2013, pp. 8, 10, 13.
- Gray & Atkinson 2003, pp. 437–438; Atkinson & Gray 2006, p. 102: “Hittite appears to have diverged from the main Proto-Indo-European stock around 8700 years ago, perhaps reflecting the initial migration out of Anatolia. Indeed, this date exactly matches estimates for the age of Europe’s first agricultural settlements in southern Greece. Following the initial split, the language tree shows the formation of separate Tocharian, Greek, and then Armenian lineages, all before 6000 BP, with all of the remaining language families formed by 4000 BP. We note that the received linguistic orthodoxy (Indo-European is only 6000 years old) does approximately fit the divergence dates we obtained for most of the branches of the tree. Only the basal branches leading to Hittite, Tocharian, Greek and Armenian are well beyond this age.”
- Georgiev 1981, p. 156: "The Proto-Greek region included Epirus, approximately up to Αυλών in the north including Paravaia, Tymphaia, Athamania, Dolopia, Amphilochia, and Acarnania), west and north Thessaly (Hestiaiotis, Perrhaibia, Tripolis, and Pieria), i.e. more or less the territory of contemporary northwestern Greece)."
- Sihler 1995
- Lengthened -ei /eː/ due to Attic analogical lengthening in comparatives.
- Schwyzer 1939, I.74–75.
- Atkinson, Quentin D.; Gray, Russel D. (2006). "Chapter 8: How Old is the Indo-European Language Family? Illumination or More Moths to the Flame?". In Forster, Peter; Renfrew, Colin. Phylogenetic Methods and the Prehistory of Languages. Cambridge: McDonald Institute for Archaeological Research. pp. 91–109. ISBN 978-1-902937-33-5.
- Beekes, Robert Stephen Paul (1995). Comparative Indo-European Linguistics. Amsterdam: John Benjamins. ISBN 90-272-2150-2.
- Buck, Carl Darling (1933). Comparative Grammar of Greek and Latin. Chicago: University of Chicago Press.
- Fortson, Benjamin W., IV (2004). Indo-European Language and Culture. Malden, MA: Blackwell Publishing. ISBN 1-4051-0316-7.
- Georgiev, Vladimir Ivanov (1981). Introduction to the History of the Indo-European Languages. Sofia: Bulgarian Academy of Sciences.
- Gray, Russel D.; Atkinson, Quentin D. (2003). "Language-tree Divergence Times Support the Anatolian Theory of Indo-European Origin". Nature 426: 435–439.
- Hamp, Eric (2013). "The Expansion of the Indo-European Languages". Sino-Platonic Papers (Philadelphia, PA: Department of East Asian Languages and Civilizations University of Pennsylvania) (239).
- Schwyzer, Eduard (1939). Griechische Grammatik: auf der Grundlage von Karl Grugmanns Griechischer Grammatik (in German). Munich: C.H. Beck.
- Sihler, Andrew L. (1995). New Comparative Grammar of Greek and Latin. New York: Oxford University Press. ISBN 0-19-508345-8.