Today, the individual Indo-European languages with the most native speakers are English, Hindi–Urdu, Spanish, Bengali, French, Russian, Portuguese, German, and Punjabi, each with over 100 million native speakers; many others are small and in danger of extinction.
In total, 46% of the world's population (3.2 billion people) speaks an Indo-European language as a first language — by far the highest of any language family. There are about 445 living Indo-European languages, according to an estimate by Ethnologue, with over two-thirds (313) of them belonging to the Indo-Iranian branch.
Another account was made by Filippo Sassetti, a merchant born in Florence in 1540, who travelled to the Indian subcontinent. Writing in 1585, he noted some word similarities between Sanskrit and Italian (these included devaḥ/dio "God", sarpaḥ/serpe "serpent", sapta/sette "seven", aṣṭa/otto "eight", and nava/nove "nine"). However, neither Stephens' nor Sassetti's observations led to further scholarly inquiry.
Franz Bopp was a pioneer in the field of comparative linguistic studies.
Ottoman Turkish traveler Evliya Çelebi visited Vienna in 1665–1666 as part of a diplomatic mission and noted a few similarities between words in German and in Persian.
Gaston Coeurdoux and others made observations of the same type. Coeurdoux made a thorough comparison of Sanskrit, Latin and Greek conjugations in the late 1760s to suggest a relationship among them. Meanwhile, Mikhail Lomonosov compared different language groups, including Slavic, Baltic ("Kurlandic"), Iranian ("Medic"), Finnish, Chinese, "Hottentot" (Khoekhoe), and others, noting that related languages (including Latin, Greek, German and Russian) must have separated in antiquity from common ancestors.
The hypothesis reappeared in 1786 when Sir William Jones first lectured on the striking similarities among three of the oldest languages known in his time: Latin, Greek, and Sanskrit, to which he tentatively added Gothic, Celtic, and Persian, though his classification contained some inaccuracies and omissions. In one of the most famous quotations in linguistics, Jones made the following prescient statement in a lecture to the Asiatic Society of Bengal in 1786, conjecturing the existence of an earlier ancestor language, which he called "a common source" but did not name:
The Sanscrit [sic] language, whatever be its antiquity, is of a wonderful structure; more perfect than the Greek, more copious than the Latin, and more exquisitely refined than either, yet bearing to both of them a stronger affinity, both in the roots of verbs and the forms of grammar, than could possibly have been produced by accident; so strong indeed, that no philologer could examine them all three, without believing them to have sprung from some common source, which, perhaps, no longer exists.[note 1]
— Sir William Jones, Third Anniversary Discourse delivered 2 February 1786, ELIOHS
Thomas Young first used the term Indo-European in 1813, deriving it from the geographical extremes of the language family: from Western Europe to North India. A synonym is Indo-Germanic (Idg. or IdG.), specifying the family's southeasternmost and northwesternmost branches. This first appeared in French (indo-germanique) in 1810 in the work of Conrad Malte-Brun; in most languages this term is now dated or less common than Indo-European, although in German indogermanisch remains the standard scientific term. A number of other synonymous terms have also been used.
Franz Bopp wrote in 1816 On the conjugational system of the Sanskrit language compared with that of Greek, Latin, Persian and Germanic and between 1833 and 1852 he wrote Comparative Grammar. This marks the beginning of Indo-European studies as an academic discipline. The classical phase of Indo-European comparative linguistics leads from this work to August Schleicher's 1861 Compendium and up to Karl Brugmann's Grundriss, published in the 1880s. Brugmann's neogrammarian reevaluation of the field and Ferdinand de Saussure's development of the laryngeal theory may be considered the beginning of "modern" Indo-European studies. The generation of Indo-Europeanists active in the last third of the 20th century (such as Calvert Watkins, Jochem Schindler, and Helmut Rix) developed a better understanding of morphology and of ablaut in the wake of Kuryłowicz's 1956 Apophony in Indo-European, who in 1927 pointed out the existence of the Hittite consonant ḫ. Kuryłowicz's discovery supported Ferdinand de Saussure's 1879 proposal of the existence of coefficients sonantiques, elements de Saussure reconstructed to account for vowel length alternations in Indo-European languages. This led to the so-called laryngeal theory, a major step forward in Indo-European linguistics and a confirmation of de Saussure's theory.
Tocharian, with proposed links to the Afanasevo culture of Southern Siberia. Extant in two dialects (Turfanian and Kuchean, or Tocharian A and B), attested from roughly the 6th to the 9th century AD. Marginalized by the Old TurkicUyghur Khaganate and probably extinct by the 10th century.
In addition to the classical ten branches listed above, several extinct and little-known languages and language-groups have existed or are proposed to have existed:
Ancient Belgian: hypothetical language associated with the proposed Nordwestblock cultural area. Speculated to be connected to Italic or Venetic, and to have certain phonological features in common with Lusitanian.
Elymian: Poorly-attested language spoken by the Elymians, one of the three indigenous (i.e. pre-Greek and pre-Punic) tribes of Sicily. Indo-European affiliation widely accepted, possibly related to Italic or Anatolian.]
Illyrian: possibly related to Albanian, Messapian, or both
Liburnian: evidence too scant and uncertain to determine anything with certainty
Paionian: extinct language once spoken north of Macedon
Phrygian: language of the ancient Phrygians. Very likely, but not certainly, a sister group to Hellenic.
Sicel: an ancient language spoken by the Sicels (Greek Sikeloi, Latin Siculi), one of the three indigenous (i.e. pre-Greek and pre-Punic) tribes of Sicily. Proposed relationship to Latin or proto-Illyrian (Pre-Indo-European) at an earlier stage.
Venetic: shares several similarities with Latin and the Italic languages, but also has some affinities with other IE languages, especially Germanic and Celtic.
Indo-European family tree in order of first attestation
Indo-European language family tree based on "Ancestry-constrained phylogenetic analysis of Indo-European languages" by Chang et al. 
Membership of languages in the Indo-European language family is determined by genealogical relationships, meaning that all members are presumed descendants of a common ancestor, Proto-Indo-European. Membership in the various branches, groups and subgroups of Indo-European is also genealogical, but here the defining factors are shared innovations among various languages, suggesting a common ancestor that split off from other Indo-European groups. For example, what makes the Germanic languages a branch of Indo-European is that much of their structure and phonology can be stated in rules that apply to all of them. Many of their common features are presumed innovations that took place in Proto-Germanic, the source of all the Germanic languages.
In the 21st century, several attempts have been made to model the phylogeny of Indo-European languages using Bayesian methodologies similar to those applied to problems in biological phylogeny. Although there are differences in absolute timing between the various analyses, there is much commonality between them, including the result that the first known language groups to diverge were the Anatolian and Tocharian language families, in that order.
The "tree model" is considered an appropriate representation of the genealogical history of a language family if communities do not remain in contact after their languages have started to diverge. In this case, subgroups defined by shared innovations form a nested pattern. The tree model is not appropriate in cases where languages remain in contact as they diversify; in such cases subgroups may overlap, and the "wave model" is a more accurate representation. Most approaches to Indo-European subgrouping to date have assumed that the tree model is by-and-large valid for Indo-European; however, there is also a long tradition of wave-model approaches.
In addition to genealogical changes, many of the early changes in Indo-European languages can be attributed to language contact. It has been asserted, for example, that many of the more striking features shared by Italic languages (Latin, Oscan, Umbrian, etc.) might well be areal features. More certainly, very similar-looking alterations in the systems of long vowels in the West Germanic languages greatly postdate any possible notion of a proto-language innovation (and cannot readily be regarded as "areal", either, because English and continental West Germanic were not a linguistic area). In a similar vein, there are many similar innovations in Germanic and Balto-Slavic that are far more likely areal features than traceable to a common proto-language, such as the uniform development of a high vowel (*u in the case of Germanic, *i/u in the case of Baltic and Slavic) before the PIE syllabic resonants *ṛ, *ḷ, *ṃ, *ṇ, unique to these two groups among IE languages, which is in agreement with the wave model. The Balkan sprachbund even features areal convergence among members of very different branches.
An extension to the Ringe-Warnow model of language evolution, suggests that early IE had featured limited contact between distinct lineages, with only the Germanic subfamily exhibiting a less treelike behaviour as it acquired some characteristics from neighbours early in its evolution. The internal diversification of especially West Germanic is cited to have been radically non-treelike.
Specialists have postulated the existence of higher-order subgroups such as Italo-Celtic, Graeco-Armenian, Graeco-Aryan or Graeco-Armeno-Aryan, and Balto-Slavo-Germanic. However, unlike the ten traditional branches, these are all controversial to a greater or lesser degree.
The Italo-Celtic subgroup was at one point uncontroversial, considered by Antoine Meillet to be even better established than Balto-Slavic. The main lines of evidence included the genitive suffix -ī; the superlative suffix -m̥mo; the change of /p/ to /kʷ/ before another /kʷ/ in the same word (as in penkʷe > *kʷenkʷe > Latin quīnque, Old Irish cóic); and the subjunctive morpheme -ā-. This evidence was prominently challenged by Calvert Watkins, while Michael Weiss has argued for the subgroup.
Evidence for a relationship between Greek and Armenian includes the regular change of the second laryngeal to a at the beginnings of words, as well as terms for "woman" and "sheep". Greek and Indo-Iranian share innovations mainly in verbal morphology and patterns of nominal derivation. Relations have also been proposed between Phrygian and Greek, and between Thracian and Armenian. Some fundamental shared features, like the aorist (a verb form denoting action without reference to duration or completion) having the perfect active particle -s fixed to the stem, link this group closer to Anatolian languages and Tocharian. Shared features with Balto-Slavic languages, on the other hand (especially present and preterit formations), might be due to later contacts.
The Indo-Hittite hypothesis proposes that the Indo-European language family consists of two main branches: one represented by the Anatolian languages and another branch encompassing all other Indo-European languages. Features that separate Anatolian from all other branches of Indo-European (such as the gender or the verb system) have been interpreted alternately as archaic debris or as innovations due to prolonged isolation. Points proffered in favour of the Indo-Hittite hypothesis are the (non-universal) Indo-European agricultural terminology in Anatolia and the preservation of laryngeals. However, in general this hypothesis is considered to attribute too much weight to the Anatolian evidence. According to another view, the Anatolian subgroup left the Indo-European parent language comparatively late, approximately at the same time as Indo-Iranian and later than the Greek or Armenian divisions. A third view, especially prevalent in the so-called French school of Indo-European studies, holds that extant similarities in non-satem languages in general—including Anatolian—might be due to their peripheral location in the Indo-European language-area and to early separation, rather than indicating a special ancestral relationship. Hans J. Holm, based on lexical calculations, arrives at a picture roughly replicating the general scholarly opinion and refuting the Indo-Hittite hypothesis.
Pink: languages with instrumental, dative and ablative plural endings (and some others) in *-m- rather than *-bh-
The division of the Indo-European languages into satem and centum groups was put forward by Peter von Bradke in 1890, although Karl Brugmann did propose a similar type of division in 1886. In the satem languages, which include the Balto-Slavic and Indo-Iranian branches, as well as (in most respects) Albanian and Armenian, the reconstructed Proto-Indo-European palatovelars remained distinct and were fricativized, while the labiovelars merged with the 'plain velars'. In the centum languages, the palatovelars merged with the plain velars, while the labiovelars remained distinct. The results of these alternative developments are exemplified by the words for "hundred" in Avestan (satem) and Latin (centum)—the initial palatovelar developed into a fricative [s] in the former, but became an ordinary velar [k] in the latter.
Rather than being a genealogical separation, the centum–satem division is commonly seen as resulting from innovative changes that spread across PIE dialect-branches over a particular geographical area; the centum–satem isogloss intersects a number of other isoglosses that mark distinctions between features in the early IE branches. It may be that the centum branches in fact reflect the original state of affairs in PIE, and only the satem branches shared a set of innovations, which affected all but the peripheral areas of the PIE dialect continuum. Kortlandt proposes that the ancestors of Balts and Slavs took part in satemization before being drawn later into the western Indo-European sphere.
From the very beginning of Indo-European studies, there have been attempts to link the Indo-European languages genealogically to other languages and language families. However, these theories remain highly controversial, and most specialists in Indo-European linguistics are sceptical or agnostic about such proposals.
Proposals linking the Indo-European languages with a single language family include:
Objections to such groupings are not based on any theoretical claim about the likely historical existence or nonexistence of such macrofamilies; it is entirely reasonable to suppose that they might have existed. The serious difficulty lies in identifying the details of actual relationships between language families, because it is very hard to find concrete evidence that transcends chance resemblance or is not equally likely explained as being due to borrowing, including Wanderwörter, which can travel very long distances. Because the signal-to-noise ratio in historical linguistics declines over time, at great enough time-depths it becomes open to reasonable doubt that one can even distinguish between signal and noise.
Scheme of Indo-European language dispersals from c. 4000 to 1000 BCE according to the widely held Kurgan hypothesis. – Center: Steppe cultures 1 (black): Anatolian languages (archaic PIE) 2 (black): Afanasievo culture (early PIE) 3 (black) Yamnaya culture expansion (Pontic-Caspian steppe, Danube Valley) (late PIE) 4A (black): Western Corded Ware 4B-C (blue & dark blue): Bell Beaker; adopted by Indo-European speakers 5A-B (red): Eastern Corded ware 5C (red): Sintashta (proto-Indo-Iranian) 6 (magenta): Andronovo 7A (purple): Indo-Aryans (Mittani) 7B (purple): Indo-Aryans (India) [NN] (dark yellow): proto-Balto-Slavic 8 (grey): Greek 9 (yellow):Iranians – [not drawn]: Armenian, expanding from western steppe
The proposed Proto-Indo-European language (PIE) is the reconstructed common ancestor of the Indo-European languages, spoken by the Proto-Indo-Europeans. From the 1960s, knowledge of Anatolian became certain enough to establish its relationship to PIE. Using the method of internal reconstruction, an earlier stage, called Pre-Proto-Indo-European, has been proposed.
The diversification of the parent language into the attested branches of daughter languages is historically unattested. The timeline of the evolution of the various daughter languages, on the other hand, is mostly undisputed, quite regardless of the question of Indo-European origins.
Using a mathematical analysis borrowed from evolutionary biology, Donald Ringe and Tandy Warnow propose the following evolutionary tree of Indo-European branches:
1500–2000: Early Modern period to present: Colonialism results in the spread of Indo-European languages to every continent, most notably Romance (North, Central and South America, North and Sub-Saharan Africa, West Asia), West Germanic (English in North America, Sub-Saharan Africa, East Asia and Australia; to a lesser extent Dutch and German), and Russian to Central Asia and North Asia.
Important languages for reconstruction
In reconstructing the history of the Indo-European languages and the form of the Proto-Indo-European language, some languages have been of particular importance. These generally include the ancient Indo-European languages that are both well-attested and documented at an early date, although some languages from later periods are important if they are particularly linguistically conservative (most notably, Lithuanian). Early poetry is of special significance because of the rigid poetic meter normally employed, which makes it possible to reconstruct a number of features (e.g. vowel length) that were either unwritten or corrupted in the process of transmission down to the earliest extant written manuscripts.
Vedic Sanskrit (c. 1500–500 BC). This language is unique in that its source documents were all composed orally, and were passed down through oral tradition (shakha schools) for c. 2,000 years before ever being written down. The oldest documents are all in poetic form; oldest and most important of all is the Rigveda (c. 1500 BC).
Ancient Greek (c. 750–400 BC). Mycenaean Greek (c. 1450 BC) is the oldest recorded form, but its value is lessened by the limited material, restricted subject matter, and highly ambiguous writing system. More important is Ancient Greek, documented extensively beginning with the two Homeric poems (the Iliad and the Odyssey, c. 750 BC).
Hittite (c. 1700–1200 BC). This is the earliest-recorded of all Indo-European languages, and highly divergent from the others due to the early separation of the Anatolian languages from the remainder. It possesses some highly archaic features found only fragmentarily, if at all, in other languages. At the same time, however, it appears to have undergone many early phonological and grammatical changes which, combined with the ambiguities of its writing system, hinder its usefulness somewhat.
Other primary sources:
Latin, attested in a huge amount of poetic and prose material in the Classical period (c. 200 BC – 100 AD) and limited older material from as early as c. 600 BC.
Gothic (the most archaic well-documented Germanic language, c. 350 AD), along with the combined witness of the other old Germanic languages: most importantly, Old English (c. 800–1000 AD), Old High German (c. 750–1000 AD) and Old Norse (c. 1100–1300 AD, with limited earlier sources dating to c. 200 AD).
Old Avestan (c. 1700–1200 BC) and Younger Avestan (c. 900 BC). Documentation is sparse, but nonetheless quite important due to its highly archaic nature.
As in other centum languages, the "plain velar" and "palatal" stops merged, reducing the number of stops from 15 to 12.
As in the other Germanic languages, the Germanic sound shift changed the realization of all stop consonants, with each consonant shifting to a different one:
bʰ → b → p → f
dʰ → d → t → θ
gʰ → g → k → x (Later initial x →h)
gʷʰ → gʷ → kʷ → xʷ (Later initial xʷ →hʷ)
Each original consonant shifted one position to the right. For example, original dʰ became d, while original d became t and original t became θ (written th in English). This is the original source of the English sounds written f, th, h and wh. Examples, comparing English with Latin, where the sounds largely remain unshifted:
For PIE p: piscis vs. fish; pēs, pēdis vs. foot; pluvium "rain" vs. flow; pater vs. father
For PIE t: trēs vs. three; māter vs. mother
For PIE d: decem vs. ten; pēdis vs. foot; quid vs. what
For PIE k: centum vs. hund(red); capere "to take" vs. have
For PIE kʷ: quid vs. what; quandō vs. when
Various further changes affected consonants in the middle or end of a word:
The voiced stops resulting from the sound shift were softened to voiced fricatives (or perhaps the sound shift directly generated fricatives in these positions).
Verner's law also turned some of the voiceless fricatives resulting from the sound shift into voiced fricatives or stops. This is why the t in Latin centum ends up as d in hund(red) rather than the expected th.
Most remaining h sounds disappeared, while remaining f and th became voiced. For example, Latin decem ends up as ten with no h in the middle (but note taíhun "ten" in Gothic, an archaic Germanic language). Similarly, the words seven and have have a voiced v (compare Latin septem, capere), while father and mother have a voiced th, although not spelled differently (compare Latin pater, māter).
None of the daughter-language families (except possibly Anatolian, particularly Luvian) reflect the plain velar stops differently from the other two series, and there is even a certain amount of dispute whether this series existed at all in PIE. The major distinction between centum and satem languages corresponds to the outcome of the PIE plain velars:
The three-way PIE distinction between voiceless, voiced and voiced aspirated stops is considered extremely unusual from the perspective of linguistic typology—particularly in the existence of voiced aspirated stops without a corresponding series of voiceless aspirated stops. None of the various daughter-language families continue it unchanged, with numerous "solutions" to the apparently unstable PIE situation:
The Indo-Aryan languages preserve the three series unchanged but have evolved a fourth series of voiceless aspirated consonants.
The Iranian languages probably passed through the same stage, subsequently changing the aspirated stops into fricatives.
Greek converted the voiced aspirates into voiceless aspirates.
Italic probably passed through the same stage, but reflects the voiced aspirates as voiceless fricatives, especially f (or sometimes plain voiced stops in Latin).
The following table presents a comparison of conjugations of the thematicpresent indicative of the verbal root *bʰer- of the English verb to bear and its reflexes in various early attested IE languages and their modern descendants or relatives, showing that all languages had in the early stage an inflectional verb system.
While similarities are still visible between the modern descendants and relatives of these ancient languages, the differences have increased over time. Some IE languages have moved from synthetic verb systems to largely periphrastic systems. In addition, the pronouns of periphrastic forms are in parentheses when they appear. Some of these verbs have undergone a change in meaning as well.
In Modern Irishbeir usually only carries the meaning to bear in the sense of bearing a child; its common meanings are to catch, grab. Apart from the first person, the forms given in the table above are dialectical or obsolete. The second and third person forms are typically instead conjugated periphrastically by adding a pronoun after the verb: beireann tú, beireann sé/sí, beireann sibh, beireann siad.
The Hindustani (Hindi and Urdu) verb bʰarnā, the continuation of the Sanskrit verb, can have a variety of meanings, but the most common is "to fill". The forms given in the table, although etymologically derived from the present indicative, now have the meaning of future subjunctive. The loss of the present indicative in Hindustani is roughly compensated by the periphrastic habitual indicative construction, using the habitual participle (etymologically from the Sanskrit present participle bʰarant-) and an auxiliary: ma͠i bʰartā hū̃, tū bʰartā hai, vah bʰartā hai, ham bʰarte ha͠i, tum bʰarte ho, ve bʰarte ha͠i (masculine forms).
German is not directly descended from Gothic, but the Gothic forms are a close approximation of what the early West Germanic forms of c. 400 AD would have looked like. The descendant of Proto-Germanic *beraną (English bear) survives in German only in the compound gebären, meaning "bear (a child)".
The Latin verb ferre is irregular, and not a good representative of a normal thematic verb. In most Romance languages such as Portuguese, other verbs now mean "to carry" (e.g. Pt. portar < Lat. portare) and ferre was borrowed and nativized only in compounds such as sofrer "to suffer" (from Latin sub- and ferre) and conferir "to confer" (from Latin "con-" and "ferre").
In Modern Greek, phero φέρω (modern transliteration fero) "to bear" is still used but only in specific contexts and is most common in such compounds as αναφέρω, διαφέρω, εισφέρω, εκφέρω, καταφέρω, προφέρω, προαναφέρω, προσφέρω etc. The form that is (very) common today is pherno φέρνω (modern transliteration ferno) meaning "to bring". Additionally, the perfective form of pherno (used for the subjunctive voice and also for the future tense) is also phero.
The dual forms are archaic in standard Lithuanian, and are only presently used in some dialects (e.g. Samogitian).
Among modern Slavic languages, only Slovene continues to have a dual number in the standard variety.
Despite being unaware of their common linguistic origin, diverse groups of Indo-European speakers continued to culturally dominate and often replace the indigenous languages of the western two-thirds of Eurasia. By the beginning of the Common Era, Indo-European peoples controlled almost the entirety of this area: the Celts western and central Europe, the Romans southern Europe, the Germanic peoples northern Europe, the Slavs eastern Europe, the Iranian peoples most of western and central Asia and parts of eastern Europe, and the Indo-Aryan peoples in the Indian subcontinent, with the Tocharians inhabiting the Indo-European frontier in western China. By the medieval period, only the Semitic, Dravidian, Caucasian, and Uralic languages, and the language isolateBasque remained of the (relatively) indigenous languages of Europe and the western half of Asia.
Despite medieval invasions by Eurasian nomads, a group to which the Proto-Indo-Europeans had once belonged, Indo-European expansion reached another peak in the early modern period with the dramatic increase in the population of the Indian subcontinent and European expansionism throughout the globe during the Age of Discovery, as well as the continued replacement and assimilation of surrounding non-Indo-European languages and peoples due to increased state centralization and nationalism. These trends compounded throughout the modern period due to the general global population growth and the results of European colonization of the Western Hemisphere and Oceania, leading to an explosion in the number of Indo-European speakers as well as the territories inhabited by them.
Due to colonization and the modern dominance of Indo-European languages in the fields of politics, global science, technology, education, finance, and sports, even many modern countries whose populations largely speak non-Indo-European languages have Indo-European languages as official languages, and the majority of the global population speaks at least one Indo-European language. The overwhelming majority of languages used on the Internet are Indo-European, with English continuing to lead the group; English in general has in many respects become the lingua franca of global communication.
^The sentence goes on to say, equally correctly as it turned out: "...here is a similar reason, though not quite so forcible, for supposing that both the Gothic and the Celtic, though blended with a very different idiom, had the same origin with the Sanscrit; and the old Persian might be added to the same family."
^Jones, William (2 February 1786). "The Third Anniversary Discourse". Electronic Library of Historiography. Universita degli Studi Firenze, taken from: Shore (Lord Teignmouth), John (1807). The Works of Sir William Jones. With a Life of the Author. Vol. III. John Stockdale and John Walker. pp. 24–46. OCLC899731310.
^Franz Bopp (2010) . Über das Conjugationssystem der Sanskritsprache : in Vergleichung mit jenem der griechischen, lateinischen, persischen und germanischen Sprache. Documenta Semiotica : Serie 1, Linguistik (2 ed.). Hildesheim: Olms.
^Kurylowicz, Jerzy (1927). "ə indo-européen et ḫ hittite". In Taszycki, W.; Doroszewski, W. (eds.). Symbolae grammaticae in honorem Ioannis Rozwadowski. Vol. 1. pp. 95–104.
^Elsie, Robert (2005). "Theodor of Shkodra (1210) and Other Early Texts". Albanian Literature: A Short History. New York/Westport/London: I.B.Tauris. p. 5.
^In his latest book, Eric Hamp supports the thesis that the Illyrian language belongs to the Northwestern group, that the Albanian language is descended from Illyrian, and that Albanian is related to Messapic which is an earlier Illyrian dialect (Comparative Studies on Albanian, 2007).
^Curtis, Matthew Cowan (30 November 2011). Slavic–Albanian Language Contact, Convergence, and Coexistence. ProQuest LLC. p. 18. ISBN978-1-267-58033-7. Retrieved 31 March 2017. So while linguists may debate about the ties between Albanian and older languages of the Balkans, and while most Albanians may take the genealogical connection to Illyrian as incontrovertible, the fact remains that there is simply insufficient evidence to connect Illyrian, Thracian, or Dacian with any language, including Albanian
^David W. Anthony, "Two IE phylogenies, three PIE migrations, and four kinds of steppe pastoralism", Journal of Language Relationship, vol. 9 (2013), pp. 1–22
^F. Ribezzo, Revue Internationale d'Onomastique, II, 1948 p. 43 sq. et III 1949, p. 45 sq., M.Almagro dans RSLig, XVI, 1950, p. 42 sq, P.Laviosa Zambotti, l.c.
^Bernard, Sergent (1995). Les Indo-Européens: Histoire, langues, mythes. Paris: Bibliothèques scientifiques Payot. pp. 84–85.
^Tribulato, Olga (December 2012). Language and Linguistic Contact in Ancient Sicily. Cambridge: Cambridge University Press. pp. 95–114. ISBN9781139248938.
^Price, Glanville (April 2000). Encyclopedia of the languages of Europe. John Wiley & Sons. p. 136. ISBN0631220399.
^Kruta, Venceslas (1991). The Celts. Thames and Hudson. p. 54.
^Fine, John (1985). The ancient Greeks: a critical history. Harvard University Press. p. 72. ISBN978-0-674-03314-6. "Most scholars now believe that the Sicans and Sicels, as well as the inhabitants of southern Italy, were basically of Illyrian stock superimposed on an aboriginal 'Mediterranean' population."
^Lejeune, Michel (1974). Manuel de la langue vénète. Heidelberg: C. Winter. p. 341.
^Pokorny, Julius (1959). Indogermanisches Etymologisches Wörterbuch. Bern. pp. 708–709, 882–884.
^Encyclopædia Britannica, vol.22, Helen Hemingway Benton Publisher, Chicago, (15th ed.) 1981, p. 593
^George S. Lane, Douglas Q. Adams,
Britannica 15th edition 22:667, "The Tocharian problem"
^The supposed autochthony of Hittites, the Indo-Hittite hypothesis and migration of agricultural "Indo-European" societies became intrinsically linked together by C. Renfrew. (Renfrew, C 2001a The Anatolian origins of Proto-Indo-European and the autochthony of the Hittites. In R. Drews ed., Greater Anatolia and the Indo-Hittite language family: 36–63. Washington, DC: Institute for the Study of Man).
^Britannica 15th edition, 22 p. 586 "Indo-European languages, The parent language, Laryngeal theory" – W.C.; pp. 589, 593 "Anatolian languages" – Philo H.J. Houwink ten Cate, H. Craig Melchert and Theo P.J. van den Hout
^Britannica 15th edition, 22 p. 594, "Indo-Hittite hypothesis"
^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; et al. (eds.). Data Analysis, Machine Learning, and Applications. Proc. of the 31st Annual Conference of the German Classification Society (GfKl), University of Freiburg, March 7–9, 2007. Studies in Classification, Data Analysis, and Knowledge Organization. Heidelberg-Berlin: Springer-Verlag. ISBN978-3-540-78239-1. The result is a partly new chain of separation for the main Indo-European branches, which fits well to the grammatical facts, as well as to the geographical distribution of these branches. In particular it clearly demonstrates that the Anatolian languages did not part as first ones and thereby refutes the Indo-Hittite hypothesis.
^Britannica 15th edition, vol.22, 1981, pp. 588, 594
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