Indo-European
Geographic distribution:	Before the 16th century, Europe, and South, Central and Southwest Asia; today worldwide.
Linguistic classification:	One of the world's major language families
Proto-language:	Proto-Indo-European
Subdivisions:	Albanian Anatolian (extinct) Armenian Balto-Slavic (Baltic and Slavic) Celtic Germanic Hellenic (Greek) Indo-Iranian Italic (includes Romance) Tocharian (extinct)
ISO 639-2 and 639-5:	ine
Countries with a majority of speakers of IE languages   Countries with an IE minority language with official status

The Indo-European languages are a family (or phylum) of several hundred related languages and dialects,^[1] including most major current languages of Europe, the Iranian plateau, and South Asia and also historically predominant in Anatolia. With written attestations appearing since the Bronze Age, in the form of the Anatolian languages and Mycenaean Greek, the Indo-European family is significant to the field of historical linguistics as possessing the longest recorded history after the Afroasiatic family.

Indo-European languages are spoken by almost three billion native speakers,^[2] the largest number for any recognised language family. Of the twenty languages with the largest numbers of native speakers according to SIL Ethnologue, twelve are Indo-European: Spanish, English, Hindi, Portuguese, Bengali, Russian, German, Marathi, French, Italian, Punjabi, and Urdu, accounting for over 1.7 billion native speakers.^[3] Several disputed proposals link Indo-European to other major language families.

History of Indo-European linguistics[link]

Suggestions of similarities between Indian and European languages began to be made by European visitors to India in the 16th century. In 1583 Thomas Stephens, an English Jesuit missionary in Goa, noted similarities between Indian languages, specifically Konkani, and Greek and Latin. These observations, however, were included in a letter to his brother which was not published until the twentieth century.^[4]

The first account by a western European to mention the ancient language Sanskrit came from Filippo Sassetti (born in Florence, Italy in 1540), a merchant who traveled 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", nava/nove "nine").^[4] However, neither Stephens's nor Sassetti's observations led to further scholarly inquiry.^[4]

In 1647, Dutch linguist and scholar Marcus Zuerius van Boxhorn noted the similarity among Indo-European languages, and supposed that they derived from a primitive common language which he called "Scythian". He included in his hypothesis Dutch, Albanian, Greek, Latin, Persian, and German, later adding Slavic, Celtic and Baltic languages. However, Van Boxhorn's suggestions did not become widely known and did not stimulate further research.

Franz Bopp, pioneer in the field of comparative linguistic studies.

Gaston Coeurdoux and others had 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 between them. Similarly, Mikhail Lomonosov compared different languages groups of the world including Slavic, Baltic ("Kurlandic"), Iranian ("Medic"), Finnish, Chinese, "Hottentot", and others. He emphatically expressed the antiquity of the linguistic stages accessible to comparative method in the drafts for his Russian Grammar (published 1755).^[5]

The hypothesis reappeared in 1786 when Sir William Jones first lectured on the striking similarities between three of the oldest languages known in his time: Latin, Greek, and Sanskrit, to which he tentatively added Gothic, Celtic, and Old Persian,^[6] though his classification contained some inaccuracies and omissions.^{[7][dead link]}

It was Thomas Young who in 1813^[8] first used the term Indo-European, which became the standard scientific term through the work of Franz Bopp, whose systematic comparison of these and other old languages supported the theory. In some nations, the term Indo-Germanic is in use; in Germany as the standard scientific term, while in other languages it is the more common term.^[9] Bopp's Comparative Grammar, appearing between 1833 and 1852, counts as the starting point of Indo-European studies as an academic discipline.

The classical phase of Indo-European comparative linguistics leads from Franz Bopp's Comparative Grammar (1833) to August Schleicher's 1861 Compendium and up to Karl Brugmann's Grundriss, published in the 1880s. Brugmann's junggrammatische 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, in the wake of Kuryłowicz's 1956 Apophonie, understanding of the ablaut.

Classification[link]

Indo-European language family

The approximate present-day distribution of the Indo-European branches within their homelands of Europe and Asia:

  Hellenic (Greek)

  Indo-Iranian

  Italic (includes Romance)

  Celtic

  Germanic

  Armenian

  Balto-Slavic (Baltic)

  Balto-Slavic (Slavic)

  Albanian

  Non-Indo-European languages

Dotted/striped areas indicate where multilingualism is common.

The various subgroups of the Indo-European language family include ten major branches, given in the chronological order of their earliest surviving written attestations:

1. Anatolian, the earliest attested branch. Isolated terms in Old Assyrian sources from the 19th century BC, Hittite texts from about the 16th century BC; extinct by Late Antiquity.
2. Hellenic, fragmentary records in Mycenaean Greek from between 1350 and 1450 BC have been found.^[10] Homeric texts date to the 8th century BC. (See Proto-Greek, History of the Greek.)
3. Indo-Iranian, descended from Proto-Indo-Iranian (dated to the late 3rd millennium BC).
   • Iranian, attested from roughly 1000 BC in the form of Avestan. Epigraphically from 520 BC in the form of Old Persian (Behistun inscription).
   • Indo-Aryan or Indic languages, attested from the late 15th to the early 14th century BC in Mitanni texts showing traces of Indo-Aryan. Epigraphically from the 3rd century BC in the form of Prakrit (Edicts of Ashoka). The Rigveda is assumed to preserve intact records via oral tradition dating from about the mid-2nd millennium BC in the form of Vedic Sanskrit.
   • Dardic
   • Nuristani
4. Italic, including Latin and its descendants (the Romance), attested from the 7th century BC.
5. Celtic, descended from Proto-Celtic. Tartessian dated from 8th century BC,^[11][12] Gaulish inscriptions date as early as the 6th century BC; Celtiberian from the 2nd century BC; Old Irish manuscript tradition from about the 8th century AD, and there are inscriptions in Old Welsh from the same period.
6. Germanic (from Proto-Germanic), earliest testimonies in runic inscriptions from around the 2nd century AD, earliest coherent texts in Gothic, 4th century AD. Old English manuscript tradition from about the 8th century AD.
7. Armenian, alphabet writings known from the beginning of the 5th century AD.
8. Tocharian, extant in two dialects (Turfanian and Kuchean), attested from roughly the 6th to the 9th century AD. Marginalized by the Old Turkic Uyghur Khaganate and probably extinct by the 10th century.
9. Balto-Slavic, believed by most Indo-Europeanists^[13] to form a phylogenetic unit, while a minority ascribes similarities to prolonged language contact.
   • Slavic (from Proto-Slavic), attested from the 9th century AD (possibly earlier; see Slavic runes), earliest texts in Old Church Slavonic.
   • Baltic, attested from the 14th century AD; for languages attested that late, they retain unusually many archaic features attributed to Proto-Indo-European (PIE).
10. Albanian, attested from the 14th century AD; Proto-Albanian likely emerged from Paleo-Balkan predecessors.^[14][15]

In addition to the classical ten branches listed above, several extinct and little-known languages have existed:

• Illyrian — related to Messapian.
• Venetic — close to Italic and possibly Continental Celtic.
• Liburnian — apparently grouped with Venetic.
• Messapian — not conclusively deciphered.
• Phrygian — language of the ancient Phrygians, possibly close to Thracian, Greek^{[citation needed]}.
• Paionian — extinct language once spoken north of Macedon.
• Thracian — possibly including Dacian.
• Dacian — possibly very close to Thracian.
• Ancient Macedonian — proposed relationships to Greek, Illyrian, Thracian, and Phrygian.
• Ligurian language — possibly not Indo-European; possibly close to or part of Celtic.
• Lusitanian — possibly related to (or part of) Celtic, or Ligurian, or Italic.

Grouping[link]

Membership of these languages in the Indo-European language family is determined by genetic relationships, meaning that all members are presumed to be descendants of a common ancestor, Proto-Indo-European. Membership in the various branches, groups and subgroups or Indo-European is also genetic, 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 so be stated in rules that apply to all of them. Many of their common features are presumed to be innovations that took place in Proto-Germanic, the source of all the Germanic languages.

Tree versus wave model[link]

To the evolutionary history of a language family, a genetic "tree model" is considered appropriate especially if communities do not remain in effective contact as their languages diverge. Exempted from this concept are shared innovations acquired by borrowing (or other means of convergence), that cannot be considered genetic. In this case the so-called "wave model" applies, featuring borrowings and no clear underlying genetic tree. 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, since 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 to be 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.

Using an extension to the Ringe-Warnow model of language evolution, early IE was confirmed to have featured limited contact between distinct lineages, while only the Germanic subfamily exhibited a less treelike behaviour as it acquired some characteristics from neighbours early in its evolution rather than from its direct ancestors. The internal diversification of especially West Germanic is cited to have been radically non-treelike.^[16]

Proposed subgroupings[link]

Specialists have postulated the existence of such subfamilies (subgroups) as Italo-Celtic, Graeco-Armenian, Graeco-Aryan, and Germanic with Balto-Slavic. The vogue for such subgroups waxes and wanes; Italo-Celtic for example used to be a standard subgroup of Indo-European, but it is now little honored, in part because much of the evidence on which it was based has turned out to have been misinterpreted.^[17]

Subgroupings of the Indo-European languages are commonly held to reflect genetic relationships and linguistic change. The generic differentiation of Proto-Indo-European into dialects and languages happened hand in hand with language contact and the spread of innovations over different territories.

Rather than being entirely genetic, the grouping of satem languages is commonly inferred as an innovative change that occurred just once, and subsequently spread over a large cohesive territory or PIE continuum that affected all but the peripheral areas.^[18] Kortlandt proposes the ancestors of Balts and Slavs took part in satemization and were then drawn into the western Indo-European sphere.^[19]

Shared features of Phrygian and Greek^[20] and of Thracian and Armenian^[21] group together with the Indo-Iranian family of Indo-European languages.^[22] 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^[23] and Tocharian. Shared features with Balto-Slavic languages, on the other hand (especially present and preterit formations), might be due to later contacts.^[24]

The Indo-Hittite hypothesis proposes the Indo-European language family to consist 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^[25] and the preservation of laryngeals.^[26] 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 early separation, rather than indicating a special ancestral relationship.^[27] Hans J. Holm, based on lexical calculations, arrives at a picture roughly replicating the general scholarly opinion and refuting the Indo-Hittite hypothesis.^[28]

Satem and centum languages[link]

The division of the Indo-European languages into a Satem vs. a Centum group was devised by von Bradke in the late 19th century.

Suggested macrofamilies[link]

Some linguists propose that Indo-European languages form part of a hypothetical Nostratic macrofamily, and attempt to relate Indo-European to other language families, such as South Caucasian, Uralic (the Indo-Uralic proposal), Dravidian, and Afroasiatic. This theory, like the similar Eurasiatic theory of Joseph Greenberg, and the Proto-Pontic postulation of John Colarusso, remains highly controversial, however, and is not accepted by most linguists in the field. Objections to such groupings are not based on any theoretical claim about the likely historical existence or non-existence 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; 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). Since the signal-to-noise ratio in historical linguistics declines steadily over time, at great enough time-depths it becomes open to reasonable doubt that it can even be possible to distinguish between signal and noise.

Evolution[link]

Proto-Indo-European[link]

Scheme of Indo-European migrations from ca. 4000 to 1000 BC according to the Kurgan hypothesis.

The Proto-Indo-European language (PIE) is the 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.

PIE was an inflected language, in which the grammatical relationships between words were signaled through inflectional morphemes (usually endings). The roots of PIE are basic morphemes carrying a lexical meaning. By addition of suffixes, they form stems, and by addition of desinences (usually endings), these form grammatically inflected words (nouns or verbs). The hypothetical Indo-European verb system is complex and, like the noun, exhibits a system of ablaut.

Diversification[link]

This unreferenced section requires citations to ensure verifiability.

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.

Indo-European languages ca. 1500 BC

Indo-European languages ca. 500 BC

Indo-European languages ca. 500 AD

• 2500 BC–2000 BC: The breakup into the proto-languages of the attested dialects is complete. Proto-Greek is spoken in the Balkans, Proto-Indo-Iranian north of the Caspian in the emerging Andronovo culture. The Bronze Age reaches Central Europe with the Beaker culture, likely composed of various Centum dialects. The Tarim mummies possibly correspond to proto-Tocharians.
• 2000 BC–1500 BC: Catacomb culture north of the Black Sea. The chariot is invented, leading to the split and rapid spread of Iranian and Indo-Aryan from the Bactria-Margiana Archaeological Complex over much of Central Asia, Northern India, Iran and Eastern Anatolia. Proto-Anatolian is split into Hittite and Luwian. The pre-Proto-Celtic Unetice culture has an active metal industry (Nebra skydisk).
• 1500 BC–1000 BC: The Nordic Bronze Age develops pre-Proto-Germanic, and the (pre)-Proto-Celtic Urnfield and Hallstatt cultures emerge in Central Europe, introducing the Iron Age. Migration of the Proto-Italic speakers into the Italian peninsula (Bagnolo stele). Redaction of the Rigveda and rise of the Vedic civilization in the Punjab. The Mycenaean civilization gives way to the Greek Dark Ages.
• 1000 BC–500 BC: The Celtic languages spread over Central and Western Europe. Baltic languages are spoken in a huge area from present-day Poland to the Ural Mountains.^[29] Proto Germanic. Homer and the beginning of Classical Antiquity. The Vedic Civilization gives way to the Mahajanapadas. Siddhartha Gautama preaches Buddhism. Zoroaster composes the Gathas, rise of the Achaemenid Empire, replacing the Elamites and Babylonia. Separation of Proto-Italic into Osco-Umbrian and Latin-Faliscan. Genesis of the Greek and Old Italic alphabets. A variety of Paleo-Balkan languages are spoken in Southern Europe.
• 500 BC–1 BC/AD: Classical Antiquity: spread of Greek and Latin throughout the Mediterranean, and during the Hellenistic period (Indo-Greeks) to Central Asia and the Hindukush. Kushan Empire, Mauryan Empire. Proto-Germanic. The Anatolian languages are extinct.
• 1 BC/AD 500: Late Antiquity, Gupta period; attestation of Armenian. Proto-Slavic. The Roman Empire and then the Migration period marginalize the Celtic languages to the British Isles.
• 500–1000: Early Middle Ages. The Viking Age forms an Old Norse koine spanning Scandinavia, the British Isles and Iceland. The Islamic conquest and the Turkic expansion results in the Arabization and Turkification of significant areas where Indo-European languages were spoken. Tocharian is extinct in the course of the Turkic expansion while Northeastern Iranian (Scytho-Sarmatian) is reduced to small refugia. Slavic languages spread over wide areas in eastern and southeastern Europe, largely replacing Romance in the Balkans (with the exception of Romanian) and whatever was left of the paleo-Balkan languages (with the exception of Albanian).
• 1000–1500: Late Middle Ages: Attestation of Albanian and Baltic.
• 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, French Canada, 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.

Sound changes[link]

As the Proto-Indo-European (PIE) language broke up, its sound system diverged as well, changing according to various sound laws evidenced in the daughter languages.

PIE is normally reconstructed with a complex system of 15 stop consonants, including an unusual three-way phonation (voicing) distinction between voiceless, voiced and "voiced aspirated" (i.e. breathy voiced) stops, and a three-way distinction among velar consonants (k-type sounds) between "palatal" ḱ ǵ ǵh, "plain velar" k g gh and labiovelar kʷ gʷ gʷh. (The correctness of the terms palatal and plain velar is disputed; see Proto-Indo-European phonology.) All daughter languages have reduced the number of distinctions among these sounds, often in divergent ways.

As an example, in English, one of the Germanic languages, the following are some of the major changes that happened:

1. As in other centum languages, the "plain velar" and "palatal" stops merged, reducing the number of stops from 15 to 12.
2. 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 → h

   gʷʰ → gʷ → kʷ → 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

3. 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).