Proto-Indo-European language

ISBN (identifier) Encyclopædia Britannica Indo-European ablaut
Infinite Construction - STEAM
Reconstruction ofIndo-European languages
RegionSee #Region
EraSee #Era
Lower-order reconstructions

Proto-Indo-European (PIE) is the theorized common ancestor of the Indo-European language family. Its proposed features have been derived by linguistic reconstruction from documented Indo-European languages. No direct record of Proto-Indo-European exists.[1]

Far more work has gone into reconstructing PIE than any other proto-language, and it is by far the best understood of all proto-languages of its age. The vast majority of linguistic work during the 19th century was devoted to the reconstruction of PIE or its daughter proto-languages (such as Proto-Germanic and Proto-Indo-Iranian), and most of the modern techniques of linguistic reconstruction (such as the comparative method) were developed as a result.

PIE is hypothesized to have been spoken as a single language from 4500 BC to 2500 BC[2] during the Late Neolithic to Early Bronze Age, though estimates vary by more than a thousand years. According to the prevailing Kurgan hypothesis, the original homeland of the Proto-Indo-Europeans may have been in the Pontic–Caspian steppe of eastern Europe. The linguistic reconstruction of PIE has also provided insight into the culture and religion of its speakers.[3]

As speakers of Proto-Indo-European became isolated from each other through the Indo-European migrations, the regional dialects of Proto-Indo-European spoken by the various groups diverged from each other, as each dialect underwent different shifts in pronunciation (the Indo-European sound laws), morphology, and vocabulary. Thus these dialects slowly but eventually transformed into the known ancient Indo-European languages. From there, further linguistic divergence led to the evolution of their current descendants, the modern Indo-European languages. Today, the descendant languages, or daughter languages, of PIE with the most native speakers are Spanish, English, Portuguese, Hindustani (Hindi and Urdu), Bengali, Russian, Punjabi, German, Persian, French, Marathi, Italian, and Gujarati.

PIE is believed to have had an elaborate system of morphology that included inflectional suffixes (analogous to English life, lives, life's, lives') as well as ablaut (vowel alterations, for example, as preserved in English sing, sang, sung) and accent. PIE nominals and pronouns had a complex system of declension, and verbs similarly had a complex system of conjugation. The PIE phonology, particles, numerals, and copula are also well-reconstructed.

Asterisks are used as a conventional mark of reconstructed words, such as *wódr̥, *ḱwṓ, or *tréyes; these forms are the reconstructed ancestors of the modern English words water, hound, and three, respectively.

Development of the hypothesis

No direct evidence of PIE exists – scholars have reconstructed PIE from its present-day descendants using the comparative method.[4]

The comparative method follows the Neogrammarian rule: the Indo-European sound laws apply without exception. The method compares languages and uses the sound laws to find a common ancestor. For example, compare the pairs of words in Italian and English: piede and foot, padre and father, pesce and fish. Since there is a consistent correspondence of the initial consonants that emerges far too frequently to be coincidental, one can assume that these languages stem from a common parent language.[5]

William Jones, an Anglo-Welsh philologist and puisne judge in Bengal, postulated the common ancestry of Sanskrit, Latin, and Greek in 1786,[6] but he was not the first to make this observation. In the 1500s, European visitors to the Indian subcontinent became aware of similarities between Indo-Iranian languages and European languages,[7] and as early as 1653 Marcus Zuerius van Boxhorn had published a proposal for a proto-language ("Scythian") for the following language families: Germanic, Romance, Greek, Baltic, Slavic, Celtic, and Iranian.[8] In a memoir sent to the Académie des Inscriptions et Belles-Lettres in 1767 Gaston-Laurent Coeurdoux, a French Jesuit who spent all his life in India, had specifically demonstrated the analogy between Sanskrit and European languages.[9] In the perspective of current academic consensus, Jones's work was less accurate than his predecessors', as he erroneously included Egyptian, Japanese and Chinese in the Indo-European languages, while omitting Hindi.

In 1818 Rasmus Christian Rask elaborated the set of correspondences to include other Indo-European languages, such as Sanskrit and Greek, and the full range of consonants involved. In 1816 Franz Bopp published On the System of Conjugation in Sanskrit in which he investigated a common origin of Sanskrit, Persian, Greek, Latin, and German. In 1833 he began publishing the Comparative Grammar of Sanskrit, Zend, Greek, Latin, Lithuanian, Old Slavic, Gothic, and German.[10]

In 1822 Jacob Grimm formulated what became known as Grimm's law as a general rule in his Deutsche Grammatik. Grimm showed correlations between the Germanic and other Indo-European languages and demonstrated that sound change systematically transforms all words of a language.[11] From the 1870s the Neogrammarians proposed that sound laws have no exceptions, as shown in Verner's law, published in 1876, which resolved apparent exceptions to Grimm's law by exploring the role that accent (stress) had played in language change.[12]

August Schleicher's A Compendium of the Comparative Grammar of the Indo-European, Sanskrit, Greek and Latin Languages (1874–77) represented an early attempt to reconstruct the proto-Indo-European language.[13]

By the early 1900s Indo-Europeanists had developed well-defined descriptions of PIE which scholars still accept today. Later, the discovery of the Anatolian and Tocharian languages added to the corpus of descendant languages. A new principle won wide acceptance in the laryngeal theory, which explained irregularities in the linguistic reconstruction of Proto-Indo-European phonology as the effects of hypothetical sounds which had disappeared from all documented languages, but which were later observed in excavated cuneiform tablets in Anatolian.

Julius Pokorny's Indogermanisches etymologisches Wörterbuch ('Indo-European Etymological Dictionary', 1959) gave a detailed, though conservative, overview of the lexical knowledge then accumulated. Jerzy Kuryłowicz's 1956 Apophonie gave a better understanding of Indo-European ablaut. From the 1960s, knowledge of Anatolian became robust enough to establish its relationship to PIE.

Historical and geographical setting

Scholars have proposed multiple hypotheses about when, where, and by whom PIE was spoken. The Kurgan hypothesis, first put forward in 1956 by Marija Gimbutas, has become the most popular of these.[18] It proposes that the Yamnaya culture associated with the kurgans (burial mounds) on the Pontic–Caspian steppe north of the Black Sea were the original speakers of PIE.[19][page needed][20]

According to the theory, PIE became widespread because its speakers from the Kurgan culture could migrate into a vast area of Europe and Asia thanks to technologies such as the domestication of the horse, herding, and the use of wheeled vehicles.[20]

The people of these cultures were nomadic pastoralists, who, according to the model, by the early 3rd millennium BC had expanded throughout the Pontic–Caspian steppe and into eastern Europe.[21]

Other theories include the Anatolian hypothesis,[22] the Armenian hypothesis, the Paleolithic Continuity Theory, and the indigenous Aryans theory.[citation needed]

Due to early language contact, there are some lexical similarities between the Proto-Kartvelian and Proto-Indo-European languages.[23]

An overview map[24] summarises theories presented above.[25]

Classification of Indo-European languages. Red: Extinct languages. White: categories or unattested proto-languages. Left half: centum languages; right half: satem languages


The table lists the main Indo-European language families.

Clade Proto-language Description Historical languages Modern descendants
Anatolian Proto-Anatolian All now extinct, the best attested being the Hittite language. Hittite, Luwian, Palaic, Lycian, Lydian None
Tocharian Proto-Tocharian An extinct branch known from manuscripts dating from the 6th to the 8th century AD, which were found in northwest China. Tocharian A, Tocharian B None
Italic Proto-Italic This included many languages, but only descendants of Latin (the Romance languages) survive. Latin, Faliscan, Umbrian, Oscan, African Romance, Dalmatian Portuguese, Galician, Spanish, Catalan, Occitan, French, Italian, Rhaeto-Romance, Romanian, Aromanian, Sardinian, Venetian, Latin (as liturgical language of the Catholic Church and official language of Vatican City)
Celtic Proto-Celtic Once spoken across Europe, but now mostly confined to its northwestern edge. Gaulish, Celtiberian, Pictish, Cumbric, Old Irish, Middle Welsh Irish, Scottish Gaelic, Welsh, Breton, Cornish, Manx
Germanic Proto-Germanic Branched into three subfamilies: West Germanic, East Germanic (now extinct), and North Germanic. Old English, Old Norse, Gothic, Frankish, Vandalic, Burgundian, Crimean Gothic English, German, Afrikaans, Dutch, Yiddish, Norwegian, Danish, Swedish, Frisian, Icelandic, Faroese
Balto-Slavic Proto-Balto-Slavic Branched into the Baltic languages and the Slavic languages. Old Prussian, Old Church Slavonic, Sudovian, Polabian, Knaaic Baltic Latvian and Lithuanian; Slavic Russian, Ukrainian, Belarusian, Polish, Czech, Slovak, Sorbian, Serbo-Croatian, Bulgarian, Slovenian, Macedonian
Indo-Iranian Proto-Indo-Iranian Branched into the Indo-Aryan, Iranian and Nuristani languages. Indic Sanskrit, Pali, Prakrit languages; Old Persian, Parthian, Old Azeri, Median, Elu, Sogdian, Saka, Avestan, Bactrian Indic Hindustani (Hindi and Urdu), Marathi, Bengali, Assamese, Odia, Konkani, Gujarati, Nepali, Dogri, Sindhi, Maithili, Sinhala, Dhivehi, Punjabi, Kashmiri; Iranic Persian, Pashto, Balochi, Kurdish, Zaza, Ossetian, Luri, Talyshi, Tati, Gilaki, Mazandarani, Semnani, Yaghnobi, Old Azeri (extinct); Nuristani, Sanskrit (revived)
Armenian Proto-Armenian Eastern Armenian, Western Armenian
Hellenic Proto-Greek Modern Greek, Pontic Greek, Tsakonian
Albanian Proto-Albanian Albanian is the only modern representative of a distinct branch of the Indo-European language family.[26] Albanian

Common subgroups of Indo-European languages which are proposed include Italo-Celtic, Graeco-Aryan, Graeco-Armenian, Graeco-Phrygian, Daco-Thracian, and Thraco-Illyrian.

Marginally attested languages

The Lusitanian language is a marginally attested language found in the area of the border between modern Portugal and Spain. The Venetic and Liburnian languages known from the North Adriatic region are sometimes classified as Italic.

The Paleo-Balkan languages, which occur in or near the Balkan peninsula, do not appear to be members of any of the subfamilies of PIE but are so poorly attested that proper classification of them is not possible. Albanian and Greek are the only surviving Indo-European languages in the group. Other major languages of this areal grouping were Phrygian, Illyrian, Thracian, and Dacian.


Proto-Indo-European phonology has been reconstructed in some detail. Notable features of the most widely accepted (but not uncontroversial) reconstruction include:

The Proto-Indo-European accent is reconstructed today as having had variable lexical stress, which could appear on any syllable and whose position often varied among different members of a paradigm (e.g. between singular and plural of a verbal paradigm). Stressed syllables received a higher pitch; therefore it is often said that PIE had a pitch accent. The location of the stress is associated with ablaut variations, especially between normal-grade vowels (/e/ and /o/) and zero-grade (i.e. lack of a vowel), but not entirely predictable from it.

The accent is best preserved in Vedic Sanskrit and (in the case of nouns) Ancient Greek, and indirectly attested in a number of phenomena in other IE languages. To account for mismatches between the accent of Vedic Sanskrit and Ancient Greek, as well as a few other phenomena, a few historical linguists prefer to reconstruct PIE as a tone language where each morpheme had an inherent tone; the sequence of tones in a word then evolved, according to that hypothesis, into the placement of lexical stress in different ways in different IE branches.[citation needed]



Proto-Indo-European roots were affix-lacking morphemes which carried the core lexical meaning of a word and were used to derive related words (e.g., "-friend-" in the English words "befriend", "friends", and "friend" by itself). Proto-Indo-European was a fusional language, in which inflectional morphemes signalled the grammatical relationships between words. This dependence on inflectional morphemes means that roots in PIE, unlike those found in English, were rarely found by themselves. A root plus a suffix formed a word stem, and a word stem plus a desinence (usually an ending) formed a word.[27]


Many morphemes in Proto-Indo-European had short e as their inherent vowel; the Indo-European ablaut is the change of this short e to short o, long e (ē), long o (ō), or no vowel. This variation in vowels occurred both within inflectional morphology (e.g., different grammatical forms of a noun or verb may have different vowels) and derivational morphology (e.g., a verb and an associated abstract verbal noun may have different vowels).[28]

Categories that PIE distinguished through ablaut were often also identifiable by contrasting endings, but the loss of these endings in some later Indo-European languages has led them to use ablaut alone to identify grammatical categories, as in the Modern English words sing, sang, sung.


Proto-Indo-European nouns are declined for eight or nine cases:[29]

Late Proto-Indo-European had three grammatical genders:

This system is probably derived from a simpler two-gender system, attested in Anatolian languages: common (or animate) and neuter (inanimate) gender.

All nominals distinguished three numbers:


Proto-Indo-European pronouns are difficult to reconstruct, owing to their variety in later languages. PIE had personal pronouns in the first and second grammatical person, but not the third person, where demonstrative pronouns were used instead. The personal pronouns had their own unique forms and endings, and some had two distinct stems; this is most obvious in the first person singular where the two stems are still preserved in English I and me. There were also two varieties for the accusative, genitive and dative cases, a stressed and an enclitic form.[31]

Personal pronouns[31]
First person Second person
Singular Plural Singular Plural
Nominative *h₁eǵ(oH/Hom) *wei *tuH *yuH
Accusative *h₁mé, *h₁me *nsmé, *nōs *twé *usmé, *wōs
Genitive *h₁méne, *h₁moi *ns(er)o-, *nos *tewe, *toi *yus(er)o-, *wos
Dative *h₁méǵʰio, *h₁moi *nsmei, *ns *tébʰio, *toi *usmei
Instrumental *h₁moí *nsmoí *toí *usmoí
Ablative *h₁med *nsmed *tued *usmed
Locative *h₁moí *nsmi *toí *usmi


Proto-Indo-European verbs, like the nouns, exhibited a system of ablaut. The most basic categorisation for the Indo-European verb was grammatical aspect. Verbs were classed as:

Verbs have at least four grammatical moods:

Verbs had two grammatical voices:

Verbs had three grammatical persons: first, second and third.

Verbs had three grammatical numbers:

Verbs were also marked by a highly developed system of participles, one for each combination of tense and voice, and an assorted array of verbal nouns and adjectival formations.

The following table shows a possible reconstruction of the PIE verb endings from Sihler, which largely represents the current consensus among Indo-Europeanists.

Sihler (1995)[32]
Athematic Thematic
Singular 1st *-mi *-oh₂
2nd *-si *-esi
3rd *-ti *-eti
Dual 1st *-wos *-owos
2nd *-th₁es *-eth₁es
3rd *-tes *-etes
Plural 1st *-mos *-omos
2nd *-te *-ete
3rd *-nti *-onti


Proto-Indo-European numerals are generally reconstructed as follows:

one *(H)óynos/*(H)óywos/*(H)óyk(ʷ)os; *sḗm (full grade), *sm̥- (zero grade)
two *d(u)wóh₁ (full grade), *dwi- (zero grade)
three *tréyes (full grade), *tri- (zero grade)
four *kʷetwóres (o-grade), *kʷ(e)twr̥- (zero grade)
(see also the kʷetwóres rule)
five *pénkʷe
six *s(w)éḱs; originally perhaps *wéḱs, with *s- under the influence of *septḿ̥
seven *septḿ̥
eight *oḱtṓ(w) or *h₃eḱtṓ(w)
nine *h₁néwn̥
ten *déḱm̥(t)

Rather than specifically 100, *ḱm̥tóm may originally have meant "a large number".[33]


Proto-Indo-European particles could be used both as adverbs and postpositions, like *upo "under, below". The postpositions became prepositions in most daughter languages. Other reconstructible particles include negators (*ne, *mē), conjunctions (*kʷe "and", *wē "or" and others) and an interjection (*wai!, an expression of woe or agony).

Derivational morphology

Proto-Indo-European employed various means of deriving words from other words, or directly from verb roots.

Internal derivation

Internal derivation was a process that derived new words through changes in accent and ablaut alone. It was not as productive as external (affixing) derivation, but is firmly established by the evidence of various later languages.

Possessive adjectives

Possessive or associated adjectives could be created from nouns through internal derivation. Such words could be used directly as adjectives, or they could be turned back into a noun without any change in morphology, indicating someone or something characterised by the adjective. They could also be used as the second element of a compound. If the first element was a noun, this created an adjective that resembled a present participle in meaning, e.g. "having much rice" or "cutting trees". When turned back into nouns, such compounds were Bahuvrihis or semantically resembled agent nouns.

In thematic stems, creating a possessive adjective involved shifting the accent one syllable to the right, for example:[34]

In athematic stems, there was a change in the accent/ablaut class. The known four classes followed an ordering, in which a derivation would shift the class one to the right:[34]

acrostatic → proterokinetic → hysterokinetic → amphikinetic

The reason for this particular ordering of the classes in derivation is not known. Some examples:


A vrddhi derivation, named after the Sanskrit grammatical term, signified "of, belonging to, descended from". It was characterised by "upgrading" the root grade, from zero to full (e) or from full to lengthened (ē). When upgrading from zero to full grade, the vowel could sometimes be inserted in the "wrong" place, creating a different stem from the original full grade.



Adjectives with accent on the thematic vowel could be turned into nouns by moving the accent back onto the root. A zero grade root could remain so, or be "upgraded" to full grade like in a vrddhi derivative. Some examples:[36]

This kind of derivation is likely related to the possessive adjectives, and can be seen as essentially the reverse of it.

Affixal derivation


The syntax of the older Indo-European languages has been studied in earnest since at least the late nineteenth century, by such scholars as Hermann Hirt and Berthold Delbrück. In the second half of the twentieth century, interest in the topic increased and led to reconstructions of Proto-Indo-European syntax.[37]

Since all the early attested IE languages were inflectional, PIE is thought to have relied primarily on morphological markers, rather than word order, to signal syntactic relationships within sentences.[38] Still, a default (unmarked) word order is thought to have existed in PIE. This was reconstructed by Jacob Wackernagel as being subject–verb–object (SVO), based on evidence in Vedic Sanskrit, and the SVO hypothesis still has some adherents, but as of 2015 the "broad consensus" among PIE scholars is that PIE would have been a subject–object–verb (SOV) language.[39]

The SOV default word order with other orders used to express emphasis (e.g., verb–subject–object to emphasise the verb) is attested in Old Indic, Old Iranian, Old Latin and Hittite, while traces of it can be found in the enclitic personal pronouns of the Tocharian languages.[38] A shift from OV to VO order is posited to have occurred in late PIE since many of the descendant languages have this order: modern Greek, Romance and Albanian prefer SVO, Insular Celtic has VSO as the default order, and even the Anatolian languages show some signs of this word order shift.[40] The context-dependent order preferences in Baltic, Slavic and Germanic are a complex topic, with some attributing them to outside influences [40] and others to internal developments.[41]

In popular culture

The Ridley Scott film Prometheus features an android named "David" (played by Michael Fassbender) who learns Proto-Indo-European to communicate with the "Engineer", an extraterrestrial whose race may have created humans. David practices PIE by reciting Schleicher's fable[42] and goes on to attempt communication with the Engineer through PIE. Linguist Dr Anil Biltoo created the film's reconstructed dialogue and had an onscreen role teaching David Schleicher's fable.[43]

The 2016 video game Far Cry Primal, set in around 10,000 BC, features dialects of an invented language based partly on PIE, intended to be its fictional ancestor.[44] Linguists constructed three dialects—Wenja, Udam and Izila—one for each of the three featured tribes.

See also


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  2. ^ Powell, Eric A. "Telling Tales in Proto-Indo-European". Archaeology. Retrieved 30 July 2017.
  3. ^ Fortson, Benjamin W. (2004). Indo-European language and culture: an introduction. Malden, Mass: Blackwell. p. 16. ISBN 1405103159. OCLC 54529041.CS1 maint: ref=harv (link)
  4. ^ "Linguistics – The comparative method". Science. Encyclopedia Britannica. Retrieved 27 July 2016.
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  8. ^ Blench, Roger (2004). "Archaeology and language: Methods and issues". In Bintliff, J. (ed.). A Companion to Archaeology (PDF). Oxford, UK: Basil Blackwell. pp. 52–74.
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  13. ^ "August Schleicher, German linguist". Encyclopædia Britannica. Retrieved 26 August 2016.
  14. ^ Bomhard 2019, p. 2.
  15. ^ Anthony & Ringe 2015, pp. 199–219.
  16. ^ Mallory 1989, p. 185.
  17. ^ Strazny 2000, p. 163.
  18. ^ See:
    • Bomhard : "This scenario is supported not only by linguistic evidence, but also by a growing body of archeological and genetic evidence. The Indo- Europeans have been identified with several cultural complexes existing in that area between 4,500—3,500 BCE. The literature supporting such a homeland is both extensive and persuasive [...]. Consequently, other scenarios regarding the possible Indo-European homeland, such as Anatolia, have now been mostly abandoned."[14]
    • Anthony & Ringe: "Archaeological evidence and linguistic evidence converge in support of an origin of Indo-European languages on the Pontic-Caspian steppes around 4,000 years BCE. The evidence is so strong that arguments in support of other hypotheses should be reexamined."[15]
    • Mallory: "The Kurgan solution is attractive and has been accepted by many archaeologists and linguists, in part or total. It is the solution one encounters in the Encyclopædia Britannica and the Grand Dictionnaire Encyclopédique Larousse."[16]
    • Strazny: "The single most popular proposal is the Pontic steppes (see the Kurgan hypothesis)..."[17]
  19. ^ Anthony, David W. (2007). The horse, the wheel, and language: how bronze-age riders from the Eurasian steppes shaped the modern world (8th reprint ed.). Princeton, N.J.: Princeton University Press. ISBN 978-0-691-05887-0.
  20. ^ a b Balter, Michael (13 February 2015). "Mysterious Indo-European homeland may have been in the steppes of Ukraine and Russia". Science. doi:10.1126/science.aaa7858. Retrieved 17 February 2015.
  21. ^ Gimbutas, Marija (1985). "Primary and Secondary Homeland of the Indo-Europeans: comments on Gamkrelidze-Ivanov articles". Journal of Indo-European Studies. 13 (1–2): 185–202.
  22. ^ Bouckaert, Remco; Lemey, P.; Dunn, M.; Greenhill, S. J.; Alekseyenko, A. V.; Drummond, A. J.; Gray, R. D.; Suchard, M. A.; et al. (24 August 2012), "Mapping the Origins and Expansion of the Indo-European Language Family" (PDF), Science, 337 (6097): 957–960, Bibcode:2012Sci...337..957B, doi:10.1126/science.1219669, hdl:11858/00-001M-0000-000F-EADF-A, PMC 4112997, PMID 22923579
  23. ^ Gamkrelidze, Th. & Ivanov, V. (1995). Indo-European and the Indo-Europeans: A Reconstruction and Historical Analysis of a Proto-Language and a Proto-Culture. 2 Vols. Berlin and New York: Mouton de Gruyter.
  24. ^ "Various hypothesis on origin of Indo-European language".
  25. ^ "Paleolithic Continuity Theory: Assumptions and Problems". Languages Of The World. 2 April 2015. Retrieved 23 January 2018.
  26. ^ "Perfect Phylogenetic Networks: A New Methodology for Reconstructing the Evolutionary History of Natural Languages, pg. 396" (PDF). Archived (PDF) from the original on 5 November 2010. Retrieved 22 September 2010.
  27. ^ Fortson (2004), p. 16.
  28. ^ Fortson (2004), pp. 73–74.
  29. ^ Fortson (2004), p. 102.
  30. ^ Fortson (2004), pp. 102, 105.
  31. ^ a b Beekes, Robert; Gabriner, Paul (1995). Comparative Indo-European linguistics: an introduction. Amsterdam: J. Benjamins Publishing Company. pp. 147, 212–217, 233, 243. ISBN 978-1556195044.
  32. ^ a b Sihler, Andrew L. (1995). New comparative grammar of Greek and Latin. New York u. a.: Oxford Univ. Press. ISBN 0-19-508345-8.
  33. ^ Lehmann, Winfried P (1993), Theoretical Bases of Indo-European Linguistics, London: Routledge, pp. 252–55, ISBN 0-415-08201-3
  34. ^ a b Jay Jasanoff. The Prehistory of the Balto-Slavic Accent. p. 21.
  35. ^ Fortson (2004:116f)
  36. ^ Jay Jasanoff. The Prehistory of the Balto-Slavic Accent. p. 22.
  37. ^ Kulikov, Leonid; Lavidas, Nikolaos, eds. (2015). "Preface". Proto-Indo-European Syntax and its Development. John Benjamins.
  38. ^ a b Mallory, J. P.; Adams, Douglas Q., eds. (1997). "Proto-Indo-European". Encyclopedia of Indo-European Culture. Taylor & Francis. p. 463.
  39. ^ Hock, Hans Henrich (2015). "Proto-Indo-European verb-finality: Reconstruction, typology, validation". In Kulikov, Leonid; Lavidas, Nikolaos (eds.). Proto-Indo-European Syntax and its Development. John Benjamins.
  40. ^ a b Lehmann, Winfred P. (1974). Proto-Indo-European Syntax. University of Texas Press. p. 250.
  41. ^ Ringe, Donald (2006). Proto-Indo-European to Proto-Germanic. Oxford University Press.
  42. ^ Roush, George (20 June 2012). "'Prometheus' Secret Revealed: What Did David Say to the Engineer". Screen Crush. Retrieved 29 July 2017.
  43. ^ O'Brien, Lucy (14 October 2012). "Designing Prometheus". IGN. Retrieved 29 July 2017.
  44. ^ Te, Zorine (26 January 2016). "Far Cry Primal Developers Talk About Uncovering History". Gamespot. CBS Interactive. Retrieved 1 October 2019.