View source for Indo-European languages

{{Short description|Language family native to Eurasia}}
{{Redirect|Indo-European|Eurasian people living in or connected with Indonesia|Indo people|other uses}}
{{Pp-move|small pp=yes}}

{{Use Oxford spelling|date=March 2025}}
{{Use dmy dates|date=March 2025}}
{{Infobox language family
| name          = Indo-European
| region        = Worldwide
| familycolor   = Indo-European
| speakers      = {{est.}} 3.4 billion
| family        = One of the world's primary [[language families]]
| protoname     = [[Proto-Indo-European]]
| child1        = Currently spoken:{{indent|1}}{{*}}[[Albanoid]]{{indent|1}}{{*}}[[Armenian language|Armenian]]{{indent|1}}{{*}}[[Balto-Slavic]]{{indent|1}}{{*}}[[Celtic languages|Celtic]]{{indent|1}}{{*}}[[Germanic languages|Germanic]]{{indent|1}}{{*}}[[Hellenic languages|Hellenic]]{{indent|1}}{{*}}[[Indo-Iranian languages|Indo-Iranian]]{{indent|1}}{{*}}[[Italic languages|Italic]]
| child2       = Extinct:{{indent|1}}{{*}}[[Anatolian languages|Anatolian]] {{Extinct}}{{indent|1}}{{*}}[[Tocharian languages|Tocharian]] {{Extinct}}
| child3       = Unclassified or poorly attested:{{indent|1}}{{*}}[[Ancient Belgian language|Ancient Belgian]] {{Extinct}}{{indent|1}}{{*}}[[Dacian language|Dacian]] {{Extinct}}{{indent|1}}{{*}}[[Dardani#language|Dardanian]] {{Extinct}}{{indent|1}}{{*}}[[Elymian language|Elymian]] {{Extinct}}{{indent|1}}{{*}}[[Liburnian language|Liburnian]] {{Extinct}}{{indent|1}}{{*}}[[Ligurian language (ancient)|Ligurian]] {{Extinct}}{{indent|1}}{{*}}[[Lusitanian language|Lusitanian]] {{Extinct}}{{indent|1}}{{*}}[[Paeonian language|Paeonian]] {{Extinct}}{{indent|1}}{{*}}[[Philistine language|Philistine]]? {{Extinct}}{{indent|1}}{{*}}[[Phrygian language|Phrygian]] {{Extinct}}{{indent|1}}{{*}}[[Thracian language|Thracian]] {{Extinct}}{{indent|1}}{{*}}[[Venetic language|Venetic]] {{Extinct}}
| iso2          = ine
| iso5          = ine
| glotto        = indo1319
| glottorefname = Indo-European
| map           = Indo-European Language Family Branches in Eurasia.png
| mapcaption    = Present-day distribution of Indo-European languages in Eurasia:
{{legend|#00CCFE|[[Albanoid]] ([[Albanian language|Albanian]])}}
{{legend|#7F007F|[[Armenian language|Armenian]]}}
{{legend|#3D6098|[[Baltic languages|Baltic]] ([[East Baltic languages|East]])}}
{{legend|#007F00|[[Slavic languages|Slavic]]}}{{legend|#FEA600|[[Celtic languages|Celtic]] ([[Brittonic languages|Brittonic]] and [[Goidelic]])}}
{{legend|#D30000|[[Germanic languages|Germanic]] ([[North Germanic languages|North]] and [[West Germanic languages|West]])}}
{{legend|#FEDC55|[[Hellenic languages|Hellenic]] ([[Greek language|Greek]])}}
{{legend|#00007F|[[Iranian languages|Iranian]]}}
{{legend|#751EB4|[[Indo-Aryan languages|Indo-Aryan]]}}
{{legend|#587F00|[[Nuristani languages|Nuristani]]}}
{{legend|#967F12|[[Italic languages|Italic]] ([[Romance languages|Romance]])}}
{{legend|#BEBEBE|Non-Indo-European languages}}
Dotted/striped areas indicate where [[multilingualism]] is common (more visible upon full enlargement of the map).
| notes         = {{ublist|{{Extinct}} indicates this branch of the language family is extinct}}
}}
{{Indo-European topics|wide=300px}}
The '''Indo-European languages''' are a [[language family]] native to the northern [[Indian subcontinent]], most of [[Europe]], and the [[Iranian plateau]], with additional native branches found in regions such as parts of [[Central Asia]] (e.g., [[Tajikistan]] and [[Afghanistan]]), southern Indian subcontinent ([[Sri Lanka]] and the [[Maldives]]) and [[Armenia]]. Historically, Indo-European languages were also spoken in [[Anatolia]] and [[Tarim Basin|Northwestern China]]. Some European languages of this family—[[English language|English]], [[French language|French]], [[Portuguese language|Portuguese]], [[Italian language|Italian]], [[Russian language|Russian]], [[Spanish language|Spanish]], and [[Dutch language|Dutch]]—have expanded through [[colonialism]] in the modern period and are now spoken across several continents. The Indo-European family is divided into several branches or sub-families, including [[Albanian language|Albanian]], [[Armenian language|Armenian]], [[Balto-Slavic]], [[Celtic languages|Celtic]], [[Germanic languages|Germanic]], [[Hellenic languages|Hellenic]], [[Indo-Iranian languages|Indo-Iranian]], and [[Italic languages|Italic]], all of which contain present-day living languages, as well as many more [[Extinct language|extinct]] branches.

Today the individual Indo-European languages with the most native speakers are English, Spanish, Portuguese, Russian, [[Hindustani language|Hindustani]], [[Bengali language|Bengali]], [[Punjabi language|Punjabi]], French, and [[German language|German]]; many others spoken by smaller groups are in danger of extinction. Over 3.4&nbsp;billion people (42% of the global population) speak an Indo-European language as a [[first language]]—by far the most of any language family. There are about 446 living Indo-European languages, according to an estimate by ''[[Ethnologue]]'', of which 313 belong to the Indo-Iranian branch.<ref>{{cite web |title=What are the largest language families? |url=http://www.ethnologue.com/guides/largest-families |publisher=Ethnologue}}</ref>

All Indo-European languages are descended from a single prehistoric language, [[linguistically reconstructed]] as [[Proto-Indo-European]], spoken sometime during the [[Neolithic]] or early [[Bronze Age]] ({{circa|3300|1200&nbsp;BC}}). The geographical location where it was spoken, the [[Proto-Indo-European homeland]], has been the object of many competing hypotheses; the academic consensus supports the [[Kurgan hypothesis]], which posits the homeland to be the [[Pontic–Caspian steppe]] in what is now [[Ukraine]] and [[Southern Russia]], associated with the [[Yamnaya culture]] and other related archaeological cultures during the 4th and early 3rd millennia&nbsp;BC. By the time the first written records appeared, Indo-European had already evolved into numerous languages, spoken across much of Europe, [[South Asia]], and part of [[Western Asia]]. Written evidence of Indo-European appeared during the Bronze Age in the form of [[Mycenaean Greek]] and the [[Anatolian languages]] of [[Hittite language|Hittite]] and [[Luwian]]. The oldest records are isolated Hittite words and names, interspersed in texts that are otherwise in the unrelated [[Akkadian language]] (a [[Semitic language]]) found in texts of the [[Assyria]]n colony of [[Kültepe]] in eastern [[Anatolia]] dating to the 20th century&nbsp;BC.<ref>{{cite book |last=Bryce |first=Trevor |date=2005 |title=Kingdom of the Hittites |edition=New |publisher=Oxford University Press |page=37 |isbn=978-0-19-928132-9}}</ref> Although no older written records of the original [[Proto-Indo-Europeans|Proto-Indo-European population]] remain, some aspects of [[Proto-Indo-European society|their culture]] and [[Proto-Indo-European mythology|their religion]] can be reconstructed from later evidence in the daughter cultures.<ref>{{Cite book |last=Mallory |first=J. P. |date=2006 |title=The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World |publisher=Oxford University Press |isbn=978-0-19-928791-8 |page=442}}</ref> The Indo-European family is significant to the field of [[historical linguistics]] as it possesses the second-longest [[recorded history]] of any known family after [[Egyptian language|Egyptian]] and the [[Semitic languages]], which belong to the [[Afroasiatic language family]]. The analysis of the family relationships between the Indo-European languages, and the reconstruction of their common source, was central to the development of the methodology of historical linguistics as an academic discipline in the 19th century.

The Indo-European language family is not considered by the current academic consensus in the field of linguistics to have any [[Genetic relationship (linguistics)|genetic relationships]] with other language families, although several [[#Proposed external relations|disputed hypotheses]] propose such relations.

== History of Indo-European linguistics ==
{{See also|Indo-European studies#History}}
During the 16th century, European visitors to the [[Indian subcontinent]] began to notice similarities among [[Indo-Aryan languages|Indo-Aryan]], [[Iranian languages|Iranian]], and [[languages of Europe|European]] languages. In 1583, English [[Jesuit]] missionary and [[Konkani language|Konkani]] scholar [[Thomas Stephens (Jesuit)|Thomas Stephens]] wrote a letter from [[Goa]] to his brother (not published until the 20th century){{sfn|Auroux|2000|p=1156}} in which he noted similarities between North Indian languages and [[Greek language|Greek]] and [[Latin]].

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').{{sfn|Auroux|2000|p=1156}} However, neither Stephens' nor Sassetti's observations led to further scholarly inquiry.{{sfn|Auroux|2000|p=1156}}

In 1647, [[Dutch people|Dutch]] linguist and scholar [[Marcus Zuerius van Boxhorn]] noted the similarity among certain Asian and European languages and theorized that they were derived from a primitive common language that he called Scythian.{{sfn|Beekes|2011|p=[https://books.google.com/books?id=W-HXnIG75PYC&pg=PA12 12] }} He included in his hypothesis [[Dutch language|Dutch]], [[Albanian language|Albanian]], [[Greek language|Greek]], [[Latin]], [[Persian language|Persian]], and [[German language|German]], later adding [[Slavic languages|Slavic]], [[Celtic languages|Celtic]], and [[Baltic languages]]. However, Van Boxhorn's suggestions did not become widely known and did not stimulate further research.

Ottoman Turkish traveller [[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-Laurent Coeurdoux|Gaston Coeurdoux]] and others made observations of the same type. Coeurdoux made a thorough comparison of Sanskrit, Latin, and Greek [[grammatical conjugation|conjugations]] in the late 1760s to suggest a relationship among them. Meanwhile, [[Mikhail Lomonosov]] compared different language groups, including Slavic, Baltic ("[[Courland|Kurlandic]]"), Iranian ("[[Median language|Medic]]"), [[Finnish language|Finnish]], [[Chinese language|Chinese]], "Hottentot" ([[Khoekhoe language|Khoekhoe]]), and others, noting that related languages (including Latin, Greek, German, and Russian) must have separated in antiquity from common ancestors.<ref name=Lomonosov>[http://feb-web.ru/feb/lomonos/texts/lo0/lo7/lo7-5952.htm M. V. Lomonosov (drafts for ''Russian Grammar'', published 1755). In: Complete Edition, Moscow, 1952, vol. 7, pp. 652–659] {{Webarchive|url=https://web.archive.org/web/20200801211720/http://feb-web.ru/feb/lomonos/texts/lo0/lo7/lo7-5952.htm |date=1 August 2020 }}:
Представимъ долготу времени, которою сіи языки раздѣлились. ... Польской и россійской языкъ коль давно раздѣлились! Подумай же, когда курляндской! Подумай же, когда латинской, греч., нѣм., росс. О глубокая древность! [Imagine the depth of time when these languages separated! ... Polish and Russian separated so long ago! Now think how long ago [this happened to] Kurlandic! Think when [this happened to] Latin, Greek, German, and Russian! Oh, great antiquity!]</ref>

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 language|Greek]], and [[Sanskrit]], to which he tentatively added [[Gothic language|Gothic]], [[Celtic languages|Celtic]], and [[Persian language|Persian]],<ref>{{cite book |last1=Poser |first1=William J. |last2=Campbell |first2=Lyle |date=1992 |chapter=Indo-European Practice and Historical Methodology |title=Proceedings of the Eighteenth Annual Meeting of the Berkeley Linguistics Society: General Session and Parasession on The Place of Morphology in a Grammar |volume=18 |issue=1 |publisher=Berkeley Linguistics Society |pages=227–228 |doi=10.3765/bls.v18i1.1574 |access-date=7 December 2022 |url=http://journals.linguisticsociety.org/proceedings/index.php/BLS/article/view/1574}}</ref> though his classification contained some inaccuracies and omissions.<ref>{{cite book |first=Roger |last=Blench |date=2004 |chapter=Archaeology and Language: methods and issues |editor=John Bintliff |title=A Companion To Archaeology |location=Oxford |publisher=Blackwell |pages=52–74 |chapter-url=http://www.rogerblench.info/Archaeology%20data/CH4-BLENCH.pdf |archive-url=https://web.archive.org/web/20060517091902/http://www.rogerblench.info/Archaeology%20data/CH4-BLENCH.pdf |archive-date=17 May 2006 |access-date=29 May 2010}} Blench erroneously included [[Egyptian language|Egyptian]], [[Japanese language|Japanese]], and [[Chinese language|Chinese]] in the Indo-European languages, while omitting [[Hindi]].</ref> 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:
{{Blockquote
 |text=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 [[Philology|philologer]] could examine them all three, without believing them to have sprung from some common source, which, perhaps, no longer exists.{{notetag|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."}}
 |author=Sir William Jones
 |title=Third Anniversary Discourse delivered 2 February 1786
 |source=ELIOHS<ref name=Jones-1807>{{cite web |title=The Third Anniversary Discourse |last1=Jones |first1=William |url=http://www.eliohs.unifi.it/testi/700/jones/Jones_Discourse_3.html |date=2 February 1786 |website=Electronic Library of Historiography |publisher=Universita degli Studi Firenze |postscript=,}} taken from: {{cite book |title=The Works of Sir William Jones. With a Life of the Author |last1=Shore |first1=John |date=1807 |volume=III |publisher=John Stockdale and John Walker |pages=24–46 |oclc=899731310}}</ref>
}}

[[Thomas Young (scientist)|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]].<ref>{{cite book |last=Robinson |first=Andrew |title=The Last Man Who Knew Everything: Thomas Young, the Anonymous Genius who Proved Newton Wrong and Deciphered the Rosetta Stone, among Other Surprising Feats |publisher=Penguin |year=2007 |isbn=978-0-13-134304-7 |url-access=registration |url=https://archive.org/details/lastmanwhoknewev00robi}}</ref><ref>In ''London Quarterly Review'' X/2 1813.; cf. {{harvnb|Szemerényi|Jones|Jones|1999|loc=p. 12 footnote 6.}}</ref> 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 [[Indo-European studies#Naming|number of other synonymous terms]] have also been used.

[[File:Franz Bopp (2).jpg|left|thumb|upright=0.75|[[Franz Bopp]] was a pioneer in the field of comparative linguistic studies.]]
[[Franz Bopp]] wrote in 1816 ''On the conjugational system of the Sanskrit language compared with that of Greek, Latin, Persian and Germanic''<ref>{{cite book |title=Über das Conjugationssystem der Sanskritsprache: in Vergleichung mit jenem der griechischen, lateinischen, persischen und germanischen Sprache |first=Franz |last=Bopp |location=Hildesheim |publisher=Olms |date=2010 |edition=2nd |series=Documenta Semiotica: Serie 1, Linguistik |orig-year=1816 |language=de}}</ref> 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 [[Jerzy Kuryłowicz|Kuryłowicz]]'s 1956 ''Apophony in Indo-European'', who in 1927 pointed out the existence of the [[Hittite phonology|Hittite consonant]] ḫ.<ref>{{Cite book |chapter=ə indo-européen et ḫ hittite |editor1-last=Taszycki |editor1-first=W. |editor2-last=Doroszewski |editor2-first=W. |title=Symbolae grammaticae in honorem Ioannis Rozwadowski |last=Kurylowicz |first=Jerzy |date=1927 |volume=1 |pages=95–104}}</ref> Kuryłowicz's discovery supported Ferdinand de Saussure's 1879 proposal of the existence of {{lang|fr|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.{{citation needed|date=May 2016}}

== Classification ==
{{See also|List of Indo-European languages}}
The various subgroups of the Indo-European language family include ten major branches, listed below in alphabetical order:
* [[Albanian language|Albanian]], attested from the 13th century;<ref name="dictalit">{{cite encyclopedia |last=Elsie |first=Robert |author-link=Robert Elsie |title=Theodor of Shkodra (1210) and Other Early Texts |encyclopedia=Albanian Literature: A Short History |page=5 |publisher=[[I. B. Tauris]] |location=New York |date=2005}}</ref> [[Proto-Albanian]] evolved from an ancient [[Paleo-Balkan language]], traditionally thought to be [[Illyrian languages|Illyrian]], or otherwise a totally unattested Balkan [[Indo-European language]] that was closely related to Illyrian and [[Messapic]].<ref>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 ({{harvnb|Hamp|2007}}).</ref><ref name="De Vaan">{{Cite book |last=De Vaan |first=Michiel |author-link=Michiel de Vaan |chapter=The phonology of Albanian |chapter-url=https://books.google.com/books?id=SuR8DwAAQBAJ&q=Ylli+Proto-Albanian&pg=PA1732 |title=Handbook of Comparative and Historical Indo-European Linguistics |editor-last=Klein |editor-first=Jared |editor-last2=Joseph |editor-first2=Brian |editor-last3=Fritz |editor-first3=Matthias |date=11 June 2018 |publisher=Walter de Gruyter |isbn=978-3-11-054243-1 |pages=1732–1749}}</ref><ref>{{cite book |last1=Curtis |first1=Matthew Cowan |title=Slavic–Albanian Language Contact, Convergence, and Coexistence |url=https://eric.ed.gov/?id=ED546136 |access-date=31 March 2017 |page=18 |quote=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 |isbn=978-1-267-58033-7 |date=30 November 2011}}</ref>
* [[Anatolian languages|Anatolian]], extinct by [[Late Antiquity]], spoken in [[Anatolia]], attested in isolated terms in [[Luwian]]/[[Hittites|Hittite]] mentioned in Semitic [[Akkadian language|Old Assyrian]] texts from the 20th and 19th centuries&nbsp;BC, [[Hittite texts]] from about 1650&nbsp;BC.<ref>{{cite web |url=http://www.leidenuniv.nl/en/researcharchive/index.php3-c=178.htm |title=The peaks and troughs of Hittite |date=2 May 2006 |website=www.leidenuniv.nl |access-date=25 November 2013 |archive-date=3 February 2017 |archive-url=https://web.archive.org/web/20170203061604/http://www.leidenuniv.nl/en/researcharchive/index.php3-c=178.htm |url-status=dead}}</ref><ref>{{cite web |url=http://oi.uchicago.edu/pdf/ar/61-70/65-66/65-66_CHD.pdf |title=The Hittite Computer Analysis Project |first=Hans G. |last=Güterbock |access-date=25 November 2013 |archive-date=2 December 2013 |archive-url=https://web.archive.org/web/20131202224845/http://oi.uchicago.edu/pdf/ar/61-70/65-66/65-66_CHD.pdf |url-status=dead}}</ref> Among the text is the  [[Anitta text]] in the [[Hittite language]], which is also the oldest known text in an Indo-European language. It is dated to 1700 BCE.<ref name="d093">{{cite web | title=Proceedings Volume 12 | website=Google | date=2009-10-14 | url=https://www.google.com/books/edition/Proceedings/Hz_lAAAAMAAJ?hl=en | access-date=2025-10-20|page=61}}</ref><ref name="f026">{{cite web | title=Anitta Text | website=Schlager Group Inc | url=https://library.schlagergroup.com/chapter/9781961844193-book-part-013 | access-date=2025-10-20}}</ref><ref name="d441">{{cite book | last=Art | first=Percival David Foundation of Chinese | title=Decorative Techniques and Styles in Asian Ceramics: A Colloquy Held 26-28 June 1978 | publisher=Percival David Foundation of Chinese Art | date=1979 | isbn=978-0-7286-0067-6 | url=https://books.google.com/books?id=W3HrAAAAMAAJ| access-date=2025-10-20 | page=36}}</ref>
* [[Armenian language|Armenian]], attested from the early 5th century&nbsp;AD. It evolved from the [[Proto-Armenian language]] which, according to the [[Armenian hypothesis]], developed ''in situ'' from the [[Proto-Indo-European language]] of the 3rd millennium&nbsp;BC.<ref>[[Tamaz V. Gamkrelidze|Gamkrelidze, Tamaz V.]]; [[Ivanov, Vyacheslav]] (1995). ''Indo-European and the Indo-Europeans: A Reconstruction and Historical Analysis of a Proto-Language and Proto-Culture. Part I: The Text. Part II: Bibliography, Indexes''. Walter de Gruyter. {{ISBN|978-3-11-081503-0}}.</ref><ref>Haber, Marc; Mezzavilla, Massimo; Xue, Yali; Comas, David; Gasparini, Paolo; Zalloua, Pierre; Tyler-Smith, Chris (2015). "Genetic evidence for an origin of the Armenians from Bronze Age mixing of multiple populations". ''European Journal of Human Genetics''. '''24''' (6): 931–936. [[bioRxiv]]&nbsp;10.1101/015396. [[Doi (identifier)|doi]]:10.1038/ejhg.2015.206. [[PMC (identifier)|PMC]]&nbsp;4820045. [[PMID]]&nbsp;26486470.</ref>
* [[Balto-Slavic]], believed by most Indo-Europeanists<ref>Such as {{harvnb|Schleicher|1874–1877|p=8}}, {{harvnb|Szemerényi|1957}}, {{harvnb|Collinge|1985}}, and {{harvnb|Beekes|1995|p=22}}.</ref> to form a phylogenetic unit, while a minority ascribes similarities to prolonged language-contact.
** [[Slavic languages|Slavic]] (from [[Proto-Slavic]]), attested from the 9th century&nbsp;AD ([[Pre-Christian Slavic writing|possibly earlier]]), earliest texts in [[Old Church Slavonic]]. Slavic languages include [[Bulgarian language|Bulgarian]], [[Russian language|Russian]], [[Polish language|Polish]], [[Czech language|Czech]], [[Slovak language|Slovak]], [[Silesian language|Silesian]], [[Kashubian language|Kashubian]], [[Macedonian language|Macedonian]], [[Serbo-Croatian]] ([[Bosnian language|Bosnian]], [[Croatian language|Croatian]], [[Montenegrin language|Montenegrin]], [[Serbian language|Serbian]]), [[Sorbian language|Sorbian]], [[Slovenian language|Slovenian]], [[Ukrainian language|Ukrainian]], [[Belarusian language|Belarusian]], and [[Rusyn language|Rusyn]].
** [[Baltic languages|Baltic]], attested from the 14th century; although attested relatively recently, they retain many archaic features attributed to [[Proto-Indo-European]] (PIE). Living examples are [[Lithuanian language|Lithuanian]] and [[Latvian language|Latvian]].
* [[Celtic languages|Celtic]] (from [[Proto-Celtic]]), attested since the 6th century&nbsp;BC; [[Lepontic]] inscriptions date as early as the 6th century&nbsp;BC; [[Celtiberian language|Celtiberian]] from the 2nd century&nbsp;BC; Primitive Irish [[Ogham inscription]]s from the 4th or 5th century&nbsp;AD, earliest inscriptions in [[Old Welsh]] from the 7th century&nbsp;AD. Modern Celtic languages include [[Welsh language|Welsh]], [[Cornish language|Cornish]], [[Breton language|Breton]], [[Scottish Gaelic]], [[Irish language|Irish]] and [[Manx language|Manx]].
* [[Germanic languages|Germanic]] (from [[Proto-Germanic]]), earliest attestations in [[runic]] inscriptions from around the 2nd century&nbsp;AD, earliest coherent texts in [[Gothic language|Gothic]], 4th century&nbsp;AD. [[Old English]] manuscript tradition from about the 8th century&nbsp;AD. Includes [[English language|English]], [[Frisian languages|Frisian]], [[German language|German]], [[Dutch language|Dutch]], [[Scots language|Scots]], [[Danish language|Danish]], [[Swedish language|Swedish]], [[Norwegian language|Norwegian]], [[Afrikaans]], [[Yiddish]], [[Low German]], [[Icelandic language|Icelandic]], [[Elfdalian]], and [[Faroese language|Faroese]].
* [[Hellenic languages|Hellenic]] (from [[Proto-Greek]], see also [[History of Greek]]); fragmentary records in [[Mycenaean language|Mycenaean]] Greek from between 1450 and 1350&nbsp;BC have been found.<ref>{{cite web |url=http://www.science20.com/news_articles/tablet_discovery_pushes_earliest_european_writing_back_150_years-77650 |title=Tablet Discovery Pushes Earliest European Writing Back 150 Years |website=Science 2.0 |date=30 March 2011}}</ref> [[Homer]]ic texts date to the 8th century&nbsp;BC.
* [[Indo-Iranian languages|Indo-Iranian]], attested {{Circa|1400&nbsp;BC|lk=no}}, descended from [[Proto-Indo-Iranian]] (dated to the late 3rd millennium&nbsp;BC).
** [[Indo-Aryan languages|Indo-Aryan]], attested from around 1400&nbsp;BC in [[Hittite language|Hittite]] texts from [[Anatolia]], showing [[Indo-Aryan superstrate in Mitanni|traces of Indo-Aryan]] words.<ref>{{cite book |title=Indian History |url=https://books.google.com/books?id=MazdaWXQFuQC&pg=SL1-PA114 |publisher=Allied Publishers |isbn=978-81-8424-568-4 |page=114 |date=1988}}</ref><ref>{{cite web |url=https://www.worldhistory.org/Mitanni/ |title=Mitanni |first=Joshua J. |last=Mark |date=28 April 2011 |website=[[World History Encyclopedia]]}}</ref> Epigraphically from the 3rd century&nbsp;BC in the form of [[Prakrit]] ([[Edicts of Ashoka]]). The [[Rigveda]] is assumed to preserve intact records [[Patha|via oral tradition]] dating from c.&nbsp;the mid-2nd millennium&nbsp;BC in the form of [[Vedic Sanskrit]]. Includes a wide range of modern languages from [[North India]], Eastern Pakistan and Bangladesh, including [[Hindustani language|Hindustani]] ([[Hindi]], [[Urdu]]), [[Bengali language|Bengali]], [[Odia language|Odia]], [[Assamese language|Assamese]], [[Punjabi language|Punjabi]], [[Kashmiri language|Kashmiri]], [[Gujarati language|Gujarati]], [[Marathi language|Marathi]], [[Sindhi language|Sindhi]] and [[Nepali language|Nepali]], as well as [[Sinhala language|Sinhala]] of [[Sri Lanka]] and [[Maldivian language|Dhivehi]] of the [[Maldives]] and [[Minicoy]].
** [[Iranian languages|Iranian]] or Iranic, attested from roughly 1000&nbsp;BC in the form of [[Avestan]]. Epigraphically from 520&nbsp;BC in the form of [[Old Persian]] ([[Behistun inscription]]). Includes [[Persian language|Persian]], [[Pashto]], [[Kurdish languages|Kurdish]], [[Balochi language|Balochi]], [[Luri language|Luri]], [[Tajik language|Tajik]], and [[Ossetian language|Ossetian]].
** [[Nuristani languages|Nuristani]], attested since the 20th century, are among the newest Indo-European languages to be studied. Includes [[Katë]], [[Wasi-wari|Prasun]], [[Askunu language|Ashkun]], [[Nuristani Kalasha]], [[Tregami]], and [[Zemiaki]].
* [[Italic languages|Italic]] (from [[Proto-Italic]]), attested from the 7th century&nbsp;BC. Includes the ancient [[Osco-Umbrian languages]], [[Faliscan language|Faliscan]], as well as [[Latin]] and its descendants, the [[Romance languages]], such as [[Italian language|Italian]] and [[French language|French]].
* [[Tocharian languages|Tocharian]], with proposed links to the [[Afanasevo culture]] of Southern Siberia.<ref>{{cite journal |first=David W. |last=Anthony |title=Two IE phylogenies, three PIE migrations, and four kinds of steppe pastoralism |journal=Journal of Language Relationship |volume=9 |date=2013 |pages=1–22 |doi=10.31826/jlr-2013-090105 |s2cid=132712913 |doi-access=free}}</ref> Extant in two dialects (Turfanian and Kuchean, or Tocharian A and B), attested during roughly the 6th–9th centuries&nbsp;AD. Marginalized by the Old Turkic [[Uyghur 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.<ref>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.</ref><ref name="Bernard">{{cite book |last1=Bernard |first1=Sergent |title=Les Indo-Européens: Histoire, langues, mythes |date=1995 |publisher=Bibliothèques scientifiques Payot |location=Paris |pages=84–85 |language=fr}}</ref>
* [[Cimmerian language|Cimmerian]]: possibly Iranic, Thracian, or Celtic
* [[Dacian language|Dacian]]: possibly very close to Thracian
* [[Elymian language|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.<ref name="Olga">{{cite book |last1=Tribulato |first1=Olga |title=Language and Linguistic Contact in Ancient Sicily |date=December 2012 |publisher=[[Cambridge University Press]] |isbn=978-1-139-24893-8 |pages=95–114}}</ref><ref>{{cite book |last1=Price |first1=Glanville |title=Encyclopedia of the languages of Europe |date=April 2000 |publisher=[[John Wiley & Sons]] |isbn=0-631-22039-9 |page=136}}</ref>
* [[Illyrian languages|Illyrian]]: possibly related to Albanian, Messapian, or both
* [[Liburnian language|Liburnian]]: evidence too scant and uncertain to determine anything with certainty
* [[Ligurian language (ancient)|Ligurian]]: possibly close to or part of Celtic.<ref name=kruta1>{{cite book |last=Kruta |first=Venceslas |date=1991 |title=The Celts |publisher=Thames and Hudson |page=54}}</ref>
* [[Lusitanian language|Lusitanian]]: possibly related to (or part of) Celtic, Ligurian, or Italic
* [[Ancient Macedonian language|Ancient Macedonian]]: proposed relationship to Greek.
* [[Messapic]]: not conclusively deciphered, often considered to be related to Albanian as the available fragmentary linguistic evidence shows common characteristic innovations and a number of significant lexical correspondences between the two languages<ref>{{cite book |last=Trumper |first=John |chapter=Some Celto-Albanian isoglosses and their implications |editor1-last=Grimaldi |editor1-first=Mirko |editor2-last=Lai |editor2-first=Rosangela |editor3-last=Franco |editor3-first=Ludovico |editor4-last=Baldi |editor4-first=Benedetta |title=Structuring Variation in Romance Linguistics and Beyond: In Honour of Leonardo M. Savoia |year=2018 |publisher=John Benjamins Publishing Company |isbn=9789027263179 |url=https://books.google.com/books?id=kAR-DwAAQBAJ}} pp. 283–286.</ref><ref>{{cite book |last=Friedman |first=Victor A. |title=The Routledge Handbook of Language Contact |chapter=The Balkans |series=Routledge Handbooks in Linguistics |editor=[[Evangelia Adamou]], [[Yaron Matras]] |publisher=Routledge |year=2020 |isbn=978-1-351-10914-7 |pages=385–403 |url=https://books.google.com/books?id=x4rvDwAAQBAJ}} p. 388</ref><ref>{{cite journal |last=Friedman |first=Victor A. |title=The Balkan Languages and Balkan Linguistics |journal=Annual Review of Anthropology |volume=40 |year=2011 |pages=275–291 |doi=10.1146/annurev-anthro-081309-145932}}</ref>
* [[Paionian language|Paionian]]: extinct language once spoken north of Macedon
* [[Phrygian language|Phrygian]]: language of the ancient [[Phrygians]]. Very likely, but not certainly, a sister group to Hellenic.
* [[Sicel language|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.<ref>{{cite book |last=Fine |first=John |date=1985 |title=The ancient Greeks: a critical history |publisher=[[Harvard University Press]] |page=72 |isbn=978-0-674-03314-6 |quote=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.}}</ref>
* [[Sorothaptic]]: proposed, pre-Celtic, Iberian language
* [[Thracian language|Thracian]]: possibly including Dacian
* [[Venetic]]: shares several similarities with Latin and the Italic languages, but also has some affinities with other IE languages, especially Germanic and Celtic.<ref>{{cite book |last1=Lejeune |first1=Michel |title=Manuel de la langue vénète |date=1974 |publisher=C. Winter |location=Heidelberg |page=341}}</ref><ref>{{cite book |last1=Pokorny |first1=Julius |title=Indogermanisches Etymologisches Wörterbuch |language=de |trans-title=Indogermanic Etymological Dictionary |date=1959 |location=Bern |publisher=Francke |pages=708–709, 882–884}}</ref>

[[File:Indo-European language tree (with major international languages highlighted).svg|thumb|upright=1.8|Indo-European family tree in order of first attestation]]
[[File:IndoEuropeanLanguageFamilyRelationsChart.jpg|thumb|upright=1.8|Indo-European language family tree based on "Ancestry-constrained phylogenetic analysis of Indo-European languages" by Chang et al.<ref name=chang />]]
Membership of languages in the Indo-European language family is determined by [[Genetic (linguistics)|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.<ref name=remco>{{cite journal |last1=Bouckaert |first1=Remco |last2=Lemey |first2=Philippe |date=24 August 2012 |title=Mapping the Origins and Expansion of the Indo-European Language Family |url= |journal=Science |volume=337 |issue=6097 |pages=957–960 |doi=10.1126/science.1219669 |pmid=22923579 |pmc=4112997 |bibcode=2012Sci...337..957B |hdl=11858/00-001M-0000-000F-EADF-A}}</ref><ref name=drinka>{{cite journal |last1=Drinka |first1=Bridget |author-link=Bridget Drinka |date=1 January 2013 |title=Phylogenetic and areal models of Indo-European relatedness: The role of contact in reconstruction |journal=Journal of Language Contact |volume=6 |issue=2 |pages=379–410 |doi=10.1163/19552629-00602009 |doi-access=free}}</ref><ref name=chang>{{cite journal |last1=Chang |first1=Will |last2=Chundra |first2=Cathcart |date=January 2015 |title=Ancestry-constrained phylogenetic analysis supports the Indo-European steppe hypothesis |url=https://www.linguisticsociety.org/sites/default/files/news/ChangEtAlPreprint.pdf |journal=[[Language (journal)|Language]] |volume=91 |issue=1 |pages=194–244 |doi=10.1353/lan.2015.0005 |s2cid=143978664 |access-date=30 September 2020}}</ref> 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.

=== Tree versus wave model ===
{{See also|Language change}}
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.<ref>{{Citation |last=François |first=Alexandre |authorlink=Alexandre François (linguist) |contribution=Trees, Waves and Linkages: Models of Language Diversification |editor1-last=Bowern |editor1-first=Claire |editor2-last=Evans |editor2-first=Bethwyn |title=The Routledge Handbook of Historical Linguistics |pages=161–189 |publisher=[[Routledge]] |place=London |year=2014 |isbn=978-0-415-52789-7 |contribution-url=https://marama.huma-num.fr/data/AlexFrancois_2014_HHL_Trees-waves-linkages_Diversification.pdf |ref=francois}}.</ref> Most approaches to Indo-European subgrouping to date have assumed that the tree model is by-and-large valid for Indo-European;<ref>{{cite journal |title=From August Schleicher to Sergei Starostin: on the development of the tree-diagram models of the Indo-European languages |last=Blažek |first=Václav |journal=[[Journal of Indo-European Studies]] |year=2007 |volume=35 |issue=1–2 |pages=82–109}}</ref> however, there is also a long tradition of wave-model approaches.<ref>{{cite book |title=Les dialectes indo-européens |language=fr |trans-title=The Indo-European dialects |publisher=Honoré Champion |last=Meillet |first=Antoine |year=1908 |location=Paris}}</ref><ref>{{cite book |title=I dialetti indoeuropei |publisher=Paideia |last=Bonfante |first=Giuliano |year=1931 |location=Brescia}}</ref>{{sfn|Porzig|1954}}

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 vowel]]s 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 ''[[Donald Ringe|Ringe]]-[[Tandy Warnow|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.<ref>{{Cite journal |last1=Nakhleh |first1=Luay |last2=Ringe |first2=Don |last3=Warnow |first3=Tandy |author3-link=Tandy Warnow |title=Perfect Phylogenetic Networks: A New Methodology for Reconstructing the Evolutionary History of Natural Languages |name-list-style=amp |date=2005 |journal=[[Language (journal)|Language]] |volume=81 |issue=2 |pages=382–420 |doi=10.1353/lan.2005.0078 |citeseerx=10.1.1.65.1791 |s2cid=162958 |url=http://www.cs.rice.edu/~nakhleh/Papers/NRWlanguage.pdf}}</ref>

=== Proposed subgroupings ===
{{Hypothetical Indo-European subfamilies}}
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.<ref>{{cite book |title=Encyclopedia of Indo-European Culture |publisher=Fitzroy Dearborn |last1=Mallory |first1=J. P. |last2=Adams |first2=D. Q. |year=1997 |location=London}}</ref>

The Italo-Celtic subgroup was at one point uncontroversial, considered by [[Antoine Meillet]] to be even better established than Balto-Slavic.{{sfn|Porzig|1954|p=39}} 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 {{lang|la|quīnque}}, Old Irish {{lang|sga|cóic}}); and the subjunctive morpheme ''-ā-''.{{sfn|Fortson|2004|p=247}} This evidence was prominently challenged by [[Calvert Watkins]],<ref>{{cite encyclopedia |title=Italo-Celtic revisited |encyclopedia=Ancient Indo-European dialects |publisher=[[University of California Press]] |last=Watkins |first=Calvert |editor1-last=Birnbaum |editor1-first=Henrik |editor2-last=Puhvel |editor2-first=Jaan |year=1966 |location=Berkeley |pages=29–50}}</ref> while Michael Weiss has argued for the subgroup.<ref>{{cite conference |title=Italo-Celtica: linguistic and cultural points of contact between Italic and Celtic |conference=Proceedings of the 23rd annual UCLA Indo-European Conference |publisher=Hempen |last=Weiss |first=Michael |editor1-last=Jamison |editor1-first=Stephanie W. |editor2-last=Melchert |editor2-first=H. Craig |editor3-last=Vine |editor3-first=Brent |year=2012 |location=Bremen |pages=151–173 |url=https://www.academia.edu/3249855 |access-date=19 February 2018 |isbn=978-3-934106-99-4}}</ref>

Evidence for a relationship between Greek and Armenian includes the regular change of the [[Laryngeal theory|second laryngeal]] to ''a'' at the beginnings of words, as well as terms for "woman" and "sheep".<ref>{{cite journal |title=Review of ''The linguistic relationship between Armenian and Greek'' by James Clackson |last=Greppin |first=James |journal=[[Language (journal)|Language]] |year=1996 |volume=72 |issue=4 |pages=804–807 |doi=10.2307/416105 |jstor=416105}}</ref> Greek and Indo-Iranian share innovations mainly in verbal morphology and patterns of nominal derivation.<ref>{{cite book |title=Indoiranisch-griechische Gemeinsamkeiten der Nominalbildung und deren indogermanische Grundlagen |language=de |trans-title=Indo-Iranian-Greek similarities in nominal formation and their Indo-European foundations |publisher=Institut für Sprachwissenschaft der Universität Innsbruck |last=Euler |first=Wolfram |author-link=Wolfram Euler |year=1979 |location=Innsbruck}}</ref> Relations have also been proposed between Phrygian and Greek,{{sfn|Lubotsky|1988}} and between Thracian and Armenian.{{sfn|Kortlandt|1988}}<ref>{{cite book |last=Renfrew |first=Colin |author-link=Colin Renfrew |date=1987 |title=Archaeology & Language. The Puzzle of the Indo-European Origins |location=London |publisher=Jonathan Cape |isbn=978-0-224-02495-2}}</ref> 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{{sfn|Encyclopædia Britannica|1981|p=593}} and Tocharian. Shared features with Balto-Slavic languages, on the other hand (especially present and preterit formations), might be due to later contacts.{{sfn|Encyclopædia Britannica|1981|loc=p. 667 George S. Lane, Douglas Q. Adams, ''The Tocharian problem''}}

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<ref>The supposed autochthony of Hittites, the Indo-Hittite hypothesis and migration of agricultural "Indo-European" societies became intrinsically linked together by Colin Renfrew ({{harvnb|Renfrew|2001|pp=36–73}}).</ref> and the preservation of laryngeals.{{sfn|Encyclopædia Britannica|1981|loc=Houwink ten Cate, H. J.; Melchert, H. Craig & van den Hout, Theo P. J. p. 586 ''The parent language, Laryngeal theory''; pp. 589, 593 ''Anatolian languages''}} 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.{{sfn|Encyclopædia Britannica|1981|loc=p. 594, ''Indo-Hittite hypothesis''}} Hans J. Holm, based on lexical calculations, arrives at a picture roughly replicating the general scholarly opinion and refuting the Indo-Hittite hypothesis.<ref>{{harvnb|Holm|2008|pp=629–636}}. 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.</ref>

=== Satem and centum languages ===
{{Main|Centum and satem languages}}
[[File:Indo-European isoglosses.png|thumb|upright=1.6|Some significant isoglosses in Indo-European daughter languages at around 500&nbsp;BC.
{{Legend|#9fc7f3|Blue: centum languages}}
{{Legend|#ef7a6e|Red: satem languages}}
{{Legend|#f6a20f|Orange: languages with [[Augment (Indo-European)|augment]]}}
{{Legend|#a1f091|Green: languages with PIE *-tt- > -ss-}}
{{Legend|#f6d3ab|Tan: languages with PIE *-tt- > -st-}}
{{Legend|#fdd1d1|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 phonology#Consonants|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 ({{lang|ae|satem}}) and Latin ({{lang|la|centum}})—the initial palatovelar developed into a fricative {{IPA|[s]}} in the former, but became an ordinary velar {{IPA|[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.{{sfn|Encyclopædia Britannica|1981|pp=588, 594}} [[Frederik Kortlandt|Kortlandt]] proposes that the ancestors of Balts and Slavs took part in satemization before being drawn later into the western Indo-European sphere.{{sfn|Kortlandt|1990}}

== Proposed external relations ==
{{More citations needed section|date=June 2021}}
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.<ref name=Kallio2018>{{cite book |last1=Kallio |first1=Petri |last2=Koivulehto |first2=Jorma |date=2018 |chapter=More remote relationships of Proto-Indo-European |editor1=Jared Klein |editor2=Brian Joseph |editor3=Matthias Fritz |title=Handbook of Comparative and Historical Indo-European Linguistics |pages=2280–2291}}</ref>

Proposals linking the Indo-European languages with a single language family include:<ref name=Kallio2018 />
* [[Indo-Uralic]], joining Indo-European with [[Uralic]]
* [[Pontic languages|Pontic]], postulated by [[John Colarusso]], which joins Indo-European with [[Northwest Caucasian]]

Other proposed families include:<ref name=Kallio2018 />
* [[Nostratic]], comprising all or some of the Eurasiatic languages and the [[Kartvelian languages|Kartvelian]], [[Dravidian languages|Dravidian]] (or wider, [[Elamo-Dravidian]]) and [[Afroasiatic]] language families
* [[Eurasiatic]], a theory championed by [[Joseph Greenberg]], comprising the [[Uralic]], [[Altaic]] and various '[[Paleosiberian]]' families ([[Ainu languages|Ainu]], [[Yukaghir languages|Yukaghir]], [[Nivkh languages|Nivkh]], [[Chukotko-Kamchatkan]], [[Eskimo–Aleut]]) and possibly others

Nostratic and Eurasiatic, in turn, have been included in even wider groupings, such as [[Borean]], a language family separately proposed by [[Harold C. Fleming]] and [[Sergei Starostin]] that encompasses almost all of the world's natural languages with the exception of those native to [[sub-Saharan Africa]], [[New Guinea]], [[Australia]], and the [[Andaman Islands]].

== Evolution ==

=== Proto-Indo-European ===
{{Main|Proto-Indo-European language}}
[[File:Indo-European expansions.jpg|thumb|upright=1.35| Scheme of Indo-European language dispersals from c.&nbsp;4000 to 1000&nbsp;BC, according to the widely held [[Kurgan hypothesis]].<br />– Center: Steppe cultures<br />1 (black): Anatolian languages (archaic PIE)<br />2 (black): Afanasievo culture (early PIE)<br />3 (black) Yamnaya culture expansion (Pontic-Caspian steppe, Danube Valley) (late PIE)<br />4A (black): Western Corded Ware<br />4B-C (blue & dark blue): Bell Beaker; adopted by Indo-European speakers<br />5A-B (red): Eastern Corded ware<br />5C (red): Sintashta (Proto-Indo-Iranian)<br />6 (magenta): Andronovo<br />7A (purple): Indo-Aryans (Mittani)<br />7B (purple): Indo-Aryans (India)<br />[NN] (dark yellow): Proto-Balto-Slavic<br />8 (grey): Greek<br />9 (yellow):Iranians<br />– [not drawn]: Armenian, expanding from western steppe]]
The proposed Proto-Indo-European language (PIE) is the [[Comparative method|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.

PIE is an [[inflected language]], in which the grammatical relationships between words were signalled through inflectional morphemes (usually endings). The [[root (linguistics)|roots]] of PIE are basic [[morpheme]]s carrying a [[lexical (semiotics)|lexical]] meaning. By addition of [[suffix]]es, they form [[stem (linguistics)|stems]], and by addition of [[Ending (linguistics)|endings]], these form grammatically inflected words ([[Indo-European noun|nouns]] or [[Indo-European verb|verbs]]). The reconstructed [[Indo-European verb]] system is complex and, like the noun, exhibits a system of [[ablaut]].

=== Diversification ===
{{See also|Indo-European migrations}}
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:{{sfn|Anthony|2007|pp=56–58}}
* Pre-[[Anatolian languages|Anatolian]] (before 3500&nbsp;BC)
* Pre-[[Tocharian languages|Tocharian]]
* Pre-Italic and Pre-Celtic (before 2500&nbsp;BC)
* Pre-Armenian and Pre-Greek (after 2500&nbsp;BC)
* Proto-[[Indo-Iranian languages|Indo-Iranian]] (2000&nbsp;BC)
* Pre-Germanic and Pre-Balto-Slavic;{{sfn|Anthony|2007|pp=56–58}} Proto-Germanic {{Circa|500&nbsp;BC|lk=no}}{{sfn|Ringe|2006|p=67}}

David Anthony proposes the following sequence:{{sfn|Anthony|2007|p=100}}
* Pre-[[Anatolian languages|Anatolian]] (4200&nbsp;BC)
* Pre-[[Tocharian languages|Tocharian]] (3700&nbsp;BC)
* [[Germanic parent language|Pre-Germanic]] (3300&nbsp;BC)
* Pre-Italic and Pre-Celtic (3000&nbsp;BC)
* Pre-Armenian (2800&nbsp;BC)
* Pre-Balto-Slavic (2800&nbsp;BC)
* Pre-Greek (2500&nbsp;BC)
* Proto-[[Indo-Iranian languages|Indo-Iranian]] (2200&nbsp;BC); split into Iranian and Old Indic 1800&nbsp;BC

From 1500&nbsp;BC the following sequence may be given:{{Citation needed|date=November 2019}}
* 1500–1000&nbsp;BC: The [[Nordic Bronze Age]] of [[Scandinavia]] develops [[pre-Proto-Germanic]], and the (pre-) Proto-Celtic [[Urnfield]] and [[Hallstatt culture|Hallstatt]] cultures emerge in Central Europe, introducing the [[Iron Age]]. Migration of the Proto-[[Italic languages|Italic]] speakers into the Italian peninsula ([[Bagnolo stele]]). [[Indo-Aryan migrations|Migration of Aryans to India]] followed by the redaction of the [[Rigveda]]; rise of the [[Vedic civilization]] and [[Iron Age in India|beginning of Iron Age]] in the [[Punjab]]. The [[Mycenaean civilization]] gives way to the [[Greek Dark Ages]]. Hittite goes extinct. [[Iranian languages|Iranian speakers]] start migrating southwards to [[Greater Iran]]. [[Balto-Slavic]] splits into ancestors of modern [[Baltic languages|Baltic]] and [[Slavic languages|Slavic]].
* 1000–500&nbsp;BC: The [[Celtic languages]] spread over Central and Western Europe, including [[Great Britain|Britain]]. [[Baltic languages]] are spoken in a huge area from present-day Poland to [[Moscow]].<ref>{{cite web |last1=Vijay |first1=John |last2=Slocum |first2=Jonathan |date=10 November 2008 |title=Indo-European Languages: Balto-Slavic Family |publisher=Linguistics Research Center, University of Texas |access-date=7 August 2010 |url=http://www.utexas.edu/cola/centers/lrc/iedocctr/ie-lg/Balto-Slavic.html |archive-url=https://web.archive.org/web/20110604200234/http://www.utexas.edu/cola/centers/lrc/iedocctr/ie-lg/Balto-Slavic.html |archive-date=4 June 2011}}</ref> [[Germanic parent language|Pre-Proto-Germanic]] gives rise to [[Proto-Germanic]] in southern Scandinavia. [[Homer]] and the beginning of [[Classical Antiquity]]. The Vedic civilization gives way to the [[Mahajanapadas]] as the Indo-Aryan tongue reaches eastwards, giving rise to the [[Greater Magadha]] cultural sphere, where [[Mahavira]] preaches [[Jainism]] and [[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]], [[Latin-Faliscan languages|Latin-Faliscan]], and possibly [[Venetic]] and [[Siculian]]. A variety of [[Paleo-Balkan languages]] besides Greek are spoken in Southern Europe, including [[Thracian language|Thracian]], [[Dacian language|Dacian]] and [[Illyrian language|Illyrian]], and in [[Anatolia]] ([[Phrygian language|Phrygian]]). Development of [[Prakrits]] across the northern Indian subcontinent, as well as migration of Indo-Aryan speakers to [[Sri Lanka]] and the [[Maldives]].
* 500–1&nbsp;BC: [[Classical Antiquity]]: spread of [[Ancient Greek|Greek]] and [[Latin]] throughout the Mediterranean and, during the [[Hellenistic period]] ([[Indo-Greeks]]), to Central Asia and the [[Hindukush]]. The Magadhan power and influence rises in ancient India, especially with the conquests of the [[Nanda Empire|Nandan]] and [[Mauryan empire]]s. Germanic speakers start migrating southwards to occupy formerly Celtic territories. [[Scythian cultures]] extend from Eastern Europe ([[Scythians|Pontic Scythians]]) to Northwest China ([[Ordos culture]]).
* 1&nbsp;BC–AD 500: [[Late Antiquity]], [[Gupta period]]; attestation of [[Armenian language|Armenian]]. [[Proto-Slavic]]. The [[Roman Empire]] and then the [[Germanic migrations]] marginalize the Celtic languages to the British Isles. [[Sogdian language|Sogdian]], an [[eastern Iranian language]], becomes the ''[[lingua franca]]'' of the [[Silk Road]] in Central Asia leading to China, due to the proliferation of [[Sogdia]]n merchants there. Greek settlements and [[Byzantine]] rule make the last Anatolian languages [[language death|extinct]]. [[Turkic languages]] start replacing [[Scythian languages]].
* 500–1000: [[Early Middle Ages]]. The [[Viking Age]] forms an Old Norse [[Koiné language|koine]] spanning Scandinavia, the British Isles and Iceland. Phrygian becomes extinct. The [[Islamic conquests]] and the [[Turkic expansion]] result in the [[Arabization]] and [[Turkification]] of significant areas where Indo-European languages were spoken, but [[Persian language|Persian]] still develops under Islamic rule and extends into [[Afghanistan]] and [[Tajikistan]]. Due to further [[Turkic migrations]], [[Tocharian languages|Tocharian]] becomes fully extinct while Scythian languages are overwhelmingly replaced. Slavic languages spread over wide areas in central, 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. Pannonian Basin is taken by the [[Magyars]] from the western [[Slavs]].
* 1000–1500: [[Late Middle Ages]]: Attestation of [[Albanian language|Albanian]] and [[Baltic languages|Baltic]]. Modern dialects of Indo-European languages start emerging.
* 1500–2000: [[Early modern Europe|early modern period]] to present: Colonialism results in the spread of Indo-European languages to every habitable continent, most notably [[Romance language|Romance]] (North, Central and South America, North and Sub-Saharan Africa, West Asia), [[West Germanic]] ([[English language|English]] in North America, Sub-Saharan Africa, East Asia and Australia; to a lesser extent Dutch and German), and [[Russian language|Russian]] to Central Asia and North Asia.

=== Key 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 [[conservative (language)|linguistically conservative]] (most notably, [[Lithuanian language|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 [[manuscript]]s.

Most noticeably:{{sfn|Beekes|2011|loc=[https://books.google.com/books?id=W-HXnIG75PYC&pg=PA30 p. 30], [https://books.google.com/books?id=W-HXnIG75PYC&pg=PA13 Skt: 13], [https://books.google.com/books?id=W-HXnIG75PYC&pg=PA20 Hitt: 20], [https://books.google.com/books?id=W-HXnIG75PYC&pg=PA24 Gk: 24]}}
* [[Vedic Sanskrit]] ({{Circa|1500–500&nbsp;BC|lk=no}}). 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]] ({{Circa|1500&nbsp;BC|lk=no}})). The oldest inscriptions in  the language of the ''Rigveda'', are [[Indo-Aryan superstrate in Mitanni|found in northern Syria]], where the  [[Mitanni|Mitanni kingdom]] was located.<ref name="k396">See [https://www.google.fr/books/edition/The_Horse_the_Wheel_and_Language/0FDqf415wqgC?hl=en&gbpv=1&pg=PA49&printsec=frontcover p.49] of [[#HWL|Anthony (2010)]].</ref>
* [[Ancient Greek]] ({{Circa|750–400&nbsp;BC|lk=no}}). [[Mycenaean Greek]] ({{Circa|1450&nbsp;BC|lk=no}}) 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]]'', {{Circa|750&nbsp;BC|lk=no}}).
* [[Hittite language|Hittite]] ({{Circa|1700–1200&nbsp;BC|lk=no}}). 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 Latin|Classical]] period ({{Circa|200&nbsp;BC{{snd}}AD&nbsp;100|lk=no}}) and limited [[Old Latin]] material from as early as {{Circa|600&nbsp;BC|lk=no}}.
* [[Gothic language|Gothic]] (the most archaic well-documented [[Germanic language]], {{Circa|AD&nbsp;350|lk=no}}), along with the combined witness of the other old Germanic languages: most importantly, [[Old English]] ({{Circa|800–1000|lk=no}}), [[Old High German]] ({{Circa|750–1000|lk=no}}) and [[Old Norse]] ({{Circa|1100–1300|lk=no}}, with limited earlier sources dating to {{Circa|AD&nbsp;200|lk=no}}).
* [[Old Avestan]] ({{Circa|1700–1200&nbsp;BC|lk=no}}) and [[Younger Avestan]] ({{Circa|900&nbsp;BC|lk=no}})). Documentation is sparse, but nonetheless quite important due to its highly archaic nature.
* Modern [[Lithuanian language|Lithuanian]], with limited records in [[Old Lithuanian]] ({{Circa|1500–1700|lk=no}}).
* [[Old Church Slavonic]] ({{Circa|900–1000|lk=no}}).

Other secondary sources, due to poor attestation:
* [[Luwian]], [[Lycian language|Lycian]], [[Lydian language|Lydian]] and other [[Anatolian languages]] ({{Circa|1400–400&nbsp;BC|lk=no}}).
* [[Oscan]], [[Umbrian]] and other [[Italic languages|Old Italic]] languages ({{Circa|600–200&nbsp;BC|lk=no}})).
* [[Old Persian]] ({{Circa|500&nbsp;BC|lk=no}}).
* [[Old Prussian]] ({{Circa|1350–1600|lk=no}}); even more archaic than Lithuanian.

Other secondary sources, due to extensive phonological changes and relatively limited attestation:{{sfn|Beekes|2011|loc=p. 30, [https://books.google.com/books?id=W-HXnIG75PYC&pg=PA19 Toch: 19], Arm: 20, Alb: 25 & [https://books.google.com/books?id=W-HXnIG75PYC&pg=PA124 124], [https://books.google.com/books?id=W-HXnIG75PYC&pg=PA27 OIr:27]}}
* [[Old Irish]] ({{Circa|AD&nbsp;700–850|lk=no}}).
* [[Tocharian language|Tocharian]] ({{Circa|AD&nbsp;500–800|lk=no}}), underwent large phonetic shifts and mergers in the proto-language, and has an almost entirely reworked declension system.
* [[Classical Armenian]] ({{Circa|AD&nbsp;400–1000|lk=no}}).<!--<ref name="Strazny2013">{{cite book |author=Philipp Strazny |title=Encyclopedia of Linguistics |url=https://books.google.com/books?id=27JOMobauYAC&pg=PA86 |date=2013 |publisher=Routledge |isbn=978-1-135-45522-4 |page=86}}</ref>-->
* [[Albanian language|Albanian]] ({{Circa|1284|lk=no}}{{snd}}present).

=== Sound changes ===
{{Main|Indo-European sound laws}}
As speakers of Proto-Indo-European (PIE) dispersed, the language's sound system diverged as well, changing according to various [[sound law]]s evidenced in the [[daughter language]]s.

PIE is normally reconstructed with a complex system of 15 [[stop consonant]]s, including an unusual three-way [[phonation]] ([[voice (phonetics)|voicing]]) distinction between [[voiceless]], [[voiced]] and "[[voiced aspirated]]" (i.e. [[breathy voiced]]) stops, and a three-way distinction among [[velar consonant]]s (''k''-type sounds) between "palatal" ''ḱ ǵ ǵh'', "plain velar" ''k g gh'' and [[Labialized velar consonant|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 language|English]], one of the [[Germanic language]]s, the following are some of the major changes that happened:
{{ordered list
|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:
: {{lang|ine-x-proto|bʰ}} → {{lang|ine-x-proto|b}} → {{lang|ine-x-proto|p}} → {{lang|ine-x-proto|f}}
: {{lang|ine-x-proto|dʰ}} → {{lang|ine-x-proto|d}} → {{lang|ine-x-proto|t}} → {{lang|ine-x-proto|θ}}
: {{lang|ine-x-proto|gʰ}} → {{lang|ine-x-proto|g}} → {{lang|ine-x-proto|k}} → {{lang|ine-x-proto|x}} (Later initial {{lang|ine-x-proto|x}} →{{lang|ine-x-proto|h}})
: {{lang|ine-x-proto|gʷʰ}} → {{lang|ine-x-proto|gʷ}} → {{lang|ine-x-proto|kʷ}} → {{lang|ine-x-proto|xʷ}} (Later initial {{lang|ine-x-proto|xʷ}} →{{lang|ine-x-proto|hʷ}})
Each original consonant shifted one position to the right. For example, original {{lang|ine-x-proto|dʰ}} became {{lang|ine-x-proto|d}}, while original {{lang|ine-x-proto|d}} became {{lang|ine-x-proto|t}} and original {{lang|ine-x-proto|t}} became {{lang|ine-x-proto|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 language|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 languages|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-satem isogloss|''centum'' and ''satem'']] languages corresponds to the outcome of the PIE plain velars:
* The "central" ''satem'' languages ([[Indo-Iranian languages|Indo-Iranian]], [[Balto-Slavic]], [[Albanian language|Albanian]], and [[Armenian language|Armenian]]) reflect both "plain velar" and labiovelar stops as plain velars, often with secondary [[Palatalization (sound change)|palatalization]] before a [[front vowel]] (''e i ē ī''). The "palatal" stops are palatalized and often appear as [[sibilant]]s (usually but not always distinct from the secondarily palatalized stops).
* The "peripheral" ''centum'' languages ([[Germanic languages|Germanic]], [[Italic languages|Italic]], [[Celtic languages|Celtic]], [[Greek language|Greek]], [[Anatolian languages|Anatolian]] and [[Tocharian language|Tocharian]]) reflect both "palatal" and "plain velar" stops as plain velars, while the labiovelars continue unchanged, often with later reduction into plain [[labial consonant|labial]] or [[velar consonant]]s.

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 language]]s preserve the three series unchanged but have evolved a fourth series of voiceless aspirated consonants.
* The [[Iranian language]]s probably passed through the same stage, subsequently changing the aspirated stops into fricatives.
* [[Greek language|Greek]] converted the voiced aspirates into voiceless aspirates.
* [[Italic languages|Italic]] probably passed through the same stage, but reflects the voiced aspirates as ''f'' or ''h'' (or sometimes plain voiced stops in [[Latin]]).
* [[Celtic languages|Celtic]], [[Balto-Slavic]], [[Anatolian languages|Anatolian]], and [[Albanian language|Albanian]] merge the voiced aspirated into plain voiced stops.
* [[Germanic languages|Germanic]] and [[Armenian language|Armenian]] change all three series in a [[chain shift]] (e.g. with ''bh b p'' becoming ''b p f'' (known as ''[[Grimm's law]]'' in Germanic)).

Among the other notable changes affecting consonants are:
* The [[Ruki sound law]] (''s'' becomes {{IPA|/ʃ/}} before ''r, u, k, i'') in the ''[[satem]]'' languages.
* Loss of prevocalic ''p'' in [[Proto-Celtic]].
* Development of prevocalic ''s'' to ''h'' in [[Proto-Greek]], with later loss of ''h'' between vowels.
* [[Verner's law]] in [[Proto-Germanic]].
* [[Grassmann's law]] (dissimilation of aspirates) independently in Proto-Greek and Proto-Indo-Iranian.

The following table shows the basic outcomes of PIE consonants in some of the most important daughter languages for the purposes of reconstruction. For a fuller table, see [[Indo-European sound laws]].
<div style="overflow-x:auto;">
{| class="wikitable" style="white-space: nowrap;"
|+ Proto-Indo-European consonants and their [[Reflex (linguistics)|reflexes]] in selected Indo-European daughter languages
! rowspan=2|PIE !! rowspan=2|[[Sanskrit|Skr.]] !! rowspan=2|[[Old Church Slavonic|O.C.S.]] !! rowspan=2|[[Lithuanian language|Lith.]] !! rowspan=2|[[Greek language|Greek]] !! rowspan=2|[[Latin]] !! rowspan=2|[[Old Irish]] !! rowspan=2|[[Gothic language|Gothic]] !! rowspan=2|English !! colspan=6|Examples
!
|- align=center
! PIE !! Eng. !! [[Sanskrit|Skr.]] !! [[Ancient Greek|Gk.]] !! [[Latin|Lat.]] !! [[Lithuanian language|Lith.]] etc.
![[Persian language|Prs]].
|- align=center
!'''{{lang|ine-x-proto|p}}'''
|'''{{lang|ine-x-proto|p}}'''; '''{{lang|ine-x-proto|ph}}'''<sup>H</sup>
| colspan="4"|'''{{lang|ine-x-proto|p}}'''
|'''{{lang|ine-x-proto|Ø}}''';<br />'''{{lang|ine-x-proto|ch}}'''<sup>T</sup> {{IPA|[x]}}
|'''{{lang|ine-x-proto|f}}''';<br />`-'''{{lang|ine-x-proto|b}}'''- {{IPA|[β]}}
|'''{{lang|ine-x-proto|f}}''';<br />-'''{{lang|ine-x-proto|v/f}}'''-
|''*pṓds ~ *ped-'' || ''foot'' || ''pád-'' || ''poús (podós)'' || ''pēs (pedis)'' || ''pãdas''
|Pi''á''de
|- align=center
!'''{{lang|ine-x-proto|t}}'''
|'''{{lang|ine-x-proto|t}}'''; '''{{lang|ine-x-proto|th}}'''<sup>H</sup>
| colspan="4"|'''{{lang|ine-x-proto|t}}'''
|'''{{lang|ine-x-proto|t}}''';<br />-'''{{lang|ine-x-proto|th}}'''- {{IPA|[θ]}}
|'''{{lang|ine-x-proto|þ}}''' {{IPA|[θ]}};<br />`-'''{{lang|ine-x-proto|d}}'''- {{IPA|[ð]}};<br />'''{{lang|ine-x-proto|t}}'''<sup>T-</sup>
|'''{{lang|ine-x-proto|th}}''';<br />`-'''{{lang|ine-x-proto|d}}'''-;<br />'''{{lang|ine-x-proto|t}}'''<sup>T-</sup>
|''*tréyes'' || ''three'' || ''tráyas''|| ''treĩs'' || ''trēs'' || ''trỹs''
|thri (old Persian)
|- align=center
!'''{{lang|ine-x-proto|ḱ}}'''
|'''{{lang|ine-x-proto|ś}}''' {{IPA|[ɕ]}}
|'''{{lang|ine-x-proto|s}}'''
|'''{{lang|ine-x-proto|š}}''' {{IPA|[ʃ]}}
| rowspan="2"|'''{{lang|ine-x-proto|k}}'''
| rowspan="2"|'''{{lang|ine-x-proto|c}}''' {{IPA|[k]}}
| rowspan="4"|'''{{lang|ine-x-proto|c}}''' {{IPA|[k]}};<br />-'''{{lang|ine-x-proto|ch}}'''- {{IPA|[x]}}
| rowspan="2"|'''{{lang|ine-x-proto|h}}''';<br />`-'''{{lang|ine-x-proto|g}}'''- {{IPA|[ɣ]}}
| rowspan="2"|'''{{lang|ine-x-proto|h}}''';<br />-'''{{lang|ine-x-proto|Ø}}'''-;<br />`-'''{{lang|ine-x-proto|y}}'''-
|''*ḱm̥tóm'' || ''hund(red)'' || ''śatám'' || ''he-katón'' || ''centum'' || ''šimtas''
|sad
|- align=center
!'''{{lang|ine-x-proto|k}}'''
| rowspan="3"|'''{{lang|ine-x-proto|k}}'''; '''{{lang|ine-x-proto|c}}'''<sup>E</sup> {{IPA|[tʃ]}};<br />'''{{lang|ine-x-proto|kh}}'''<sup>H</sup>
| rowspan="3"|'''{{lang|ine-x-proto|k}}''';<br />'''{{lang|ine-x-proto|č}}'''<sup>E</sup> {{IPA|[tʃ]}};<br />'''{{lang|ine-x-proto|c}}'''<sup>E'</sup> {{IPA|[ts]}}
| rowspan="3"|'''{{lang|ine-x-proto|k}}'''
|''*kreuh₂''<br /> "raw meat" || OE ''hrēaw''<br /> ''raw'' || ''kravíṣ-'' || ''kréas'' || ''cruor'' || ''kraûjas''
|xore''š''
|- align=center
!rowspan=2|'''{{lang|ine-x-proto|kʷ}}'''
|rowspan=2|'''{{lang|ine-x-proto|p}}''';<br />'''{{lang|ine-x-proto|t}}'''<sup>E</sup>;<br />'''{{lang|ine-x-proto|k}}'''<sup>(u)</sup>
|rowspan=2|'''{{lang|ine-x-proto|qu}}''' {{IPA|[kʷ]}};<br />'''{{lang|ine-x-proto|c}}'''<sup>(O)</sup> {{IPA|[k]}}
|rowspan=2|'''{{lang|ine-x-proto|ƕ}}''' {{IPA|[ʍ]}};<br />`-'''{{lang|ine-x-proto|gw/w}}'''-
|rowspan=2|'''{{lang|ine-x-proto|wh}}''';<br />`-'''{{lang|ine-x-proto|w}}'''-
| ''*kʷid, kʷod'' || ''what'' || ''kím'' || ''tí'' || ''quid, quod'' ||''kas'', ''kad''
|ce, ci
|- align=center
| ''*kʷekʷlom'' || ''wheel'' || ''cakrá-'' || ''kúklos'' || || ''kãklas''
|carx
|- align=center
!'''{{lang|ine-x-proto|b}}'''
|'''{{lang|ine-x-proto|b}}'''; '''{{lang|ine-x-proto|bh}}'''<sup>H</sup>
| colspan="4"|'''{{lang|ine-x-proto|b}}'''
|'''{{lang|ine-x-proto|b}}''' {{IPA|[b]}};<br />-'''{{IPA|[β]}}'''-
| colspan="2"|'''{{lang|ine-x-proto|p}}'''
|- align=center
!'''{{lang|ine-x-proto|d}}'''
|'''{{lang|ine-x-proto|d}}'''; '''{{lang|ine-x-proto|dh}}'''<sup>H</sup>
| colspan="4"|'''{{lang|ine-x-proto|d}}'''
|'''{{lang|ine-x-proto|d}}''' {{IPA|[d]}};<br />-{{IPA|[ð]}}-
| colspan="2"|'''{{lang|ine-x-proto|t}}'''
| ''*déḱm̥(t)'' || ''ten'',<br />[[Gothic language|Goth.]] ''taíhun'' || ''dáśa'' || ''déka'' || ''decem'' || ''dẽšimt''
|dah
|- align=center
!'''{{lang|ine-x-proto|ǵ}}'''
|'''{{lang|ine-x-proto|j}}''' {{IPA|[dʒ]}};<br />'''{{lang|ine-x-proto|h}}'''<sup>H</sup> {{IPA|[ɦ]}}
|'''{{lang|ine-x-proto|z}}'''
|'''{{lang|ine-x-proto|ž}}''' {{IPA|[ʒ]}}
| colspan="2" rowspan="2"|'''{{lang|ine-x-proto|g}}'''
| rowspan="2"|'''{{lang|ine-x-proto|g}}''' {{IPA|[ɡ]}};<br />-{{IPA|[ɣ]}}-
| rowspan="2"|'''{{lang|ine-x-proto|k}}'''
| rowspan="2"|'''{{lang|ine-x-proto|c / k}}''';<br />'''{{lang|ine-x-proto|ch}}'''<sup>E'</sup>
| ''*ǵénu, *ǵnéu-'' || OE ''cnēo''<br /> ''knee'' || ''jā́nu'' || ''gónu'' || ''genu'' ||
|z''ánu''
|- align=center
!'''{{lang|ine-x-proto|g}}'''
| rowspan="2"|'''{{lang|ine-x-proto|g}}''';<br /> '''{{lang|ine-x-proto|j}}'''<sup>E</sup> {{IPA|[dʒ]}};<br />'''{{lang|ine-x-proto|gh}}'''<sup>H</sup>;<br /> '''{{lang|ine-x-proto|h}}'''<sup>H,E</sup> {{IPA|[ɦ]}}
| rowspan="2"|'''{{lang|ine-x-proto|g}}''';<br />'''{{lang|ine-x-proto|ž}}'''<sup>E</sup> {{IPA|[ʒ]}};<br />'''{{lang|ine-x-proto|dz}}'''<sup>E'</sup>
| rowspan="2"|'''{{lang|ine-x-proto|g}}'''
|''*yugóm'' || ''yoke'' || ''yugám'' || ''zugón'' || ''iugum'' || ''jùngas''
|yugh
|- align=center
!'''{{lang|ine-x-proto|gʷ}}'''
|'''{{lang|ine-x-proto|b}}''';<br />'''{{lang|ine-x-proto|d}}'''<sup>e</sup>;<br />'''{{lang|ine-x-proto|g}}'''<sup>(u)</sup>
|'''{{lang|ine-x-proto|u}}''' {{IPA|[w > v]}};<br />'''{{lang|ine-x-proto|gu}}'''<sup>n−</sup> {{IPA|[ɡʷ]}}
| rowspan="2"|'''{{lang|ine-x-proto|b}}''' {{IPA|[b]}};<br />-{{IPA|[β]}}-
|'''{{lang|ine-x-proto|q}}''' {{IPA|[kʷ]}}
|'''{{lang|ine-x-proto|qu}}'''
| ''*gʷīw-'' || ''quick''<br />"alive" || ''jīvá-'' || ''bíos'',<br />''bíotos'' || ''vīvus'' || ''gývas''
|ze-
|- align=center
!'''{{lang|ine-x-proto|bʰ}}'''
|'''{{lang|ine-x-proto|bh}}''';<br /> '''{{lang|ine-x-proto|b}}'''<sup>..Ch</sup>
| colspan="2"|'''{{lang|ine-x-proto|b}}'''
|'''{{lang|ine-x-proto|ph}}''';<br /> '''{{lang|ine-x-proto|p}}'''<sup>..Ch</sup>
|'''{{lang|ine-x-proto|f}}'''-;<br />'''{{lang|ine-x-proto|b}}'''
|'''{{lang|ine-x-proto|b}}''' {{IPA|[b]}};<br />-{{IPA|[β]}}-;<br />-'''{{lang|ine-x-proto|f}}'''
|'''{{lang|ine-x-proto|b}}''';<br />-'''{{lang|ine-x-proto|v/f}}'''-<sup>(rl)</sup>
| ''*bʰéroh₂'' || ''bear'' "carry" || ''bhar-'' || ''phérō'' || ''ferō'' || [[Old Church Slavonic|OCS]] ''berǫ''
|bar-
|- align=center
!'''{{lang|ine-x-proto|dʰ}}'''
|'''{{lang|ine-x-proto|dh}}''';<br /> '''{{lang|ine-x-proto|d}}'''<sup>..Ch</sup>
| colspan="2"|'''{{lang|ine-x-proto|d}}'''
|'''{{lang|ine-x-proto|th}}''';<br /> '''{{lang|ine-x-proto|t}}'''<sup>..Ch</sup>
|'''{{lang|ine-x-proto|f}}'''-;<br />'''{{lang|ine-x-proto|d}}''';<br />'''{{lang|ine-x-proto|b}}'''<sup>(r),l,u-</sup>
|'''{{lang|ine-x-proto|d}}''' {{IPA|[d]}};<br />-{{IPA|[ð]}}-
|'''{{lang|ine-x-proto|d}}''' {{IPA|[d]}};<br />-{{IPA|[ð]}}-;<br />-'''{{lang|ine-x-proto|þ}}'''
|'''{{lang|ine-x-proto|d}}'''
|''*dʰwer-, dʰur-'' || ''door'' || ''dvā́raḥ'' || ''thurā́'' || ''forēs'' || ''dùrys''
|dar
|- align=center
!'''{{lang|ine-x-proto|ǵʰ}}'''
|'''{{lang|ine-x-proto|h}}''' {{IPA|[ɦ]}};<br /> '''{{lang|ine-x-proto|j}}'''<sup>..Ch</sup>
|'''{{lang|ine-x-proto|z}}'''
|'''{{lang|ine-x-proto|ž}}''' {{IPA|[ʒ]}}
| rowspan="2"|'''{{lang|ine-x-proto|kh}}''';<br /> '''{{lang|ine-x-proto|k}}'''<sup>..Ch</sup>
| rowspan="2"|'''{{lang|ine-x-proto|h}}''';<br />'''{{lang|ine-x-proto|h/g}}'''<sup>R</sup>
| rowspan="4"|'''{{lang|ine-x-proto|g}}''' {{IPA|[ɡ]}};<br />-{{IPA|[ɣ]}}-
| rowspan="2"|'''{{lang|ine-x-proto|g}}''';<br />-'''{{lang|ine-x-proto|g}}'''- {{IPA|[ɣ]}};<br />-'''{{lang|ine-x-proto|g}}''' {{IPA|[x]}}
| rowspan="2"|'''{{lang|ine-x-proto|g}}''';<br />-'''{{lang|ine-x-proto|y/w}}'''-<sup>(rl)</sup>
| ''*ǵʰans-'' || ''goose'',<br /> [[Old High German|OHG]] ''gans'' || ''haṁsáḥ'' || ''khḗn'' || ''(h)ānser'' || ''žąsìs''
|gh''áz''
|- align=center
!'''{{lang|ine-x-proto|gʰ}}'''
| rowspan="3"|'''{{lang|ine-x-proto|gh}}''';<br />'''{{lang|ine-x-proto|h}}'''<sup>E</sup> {{IPA|[ɦ]}};<br /> '''{{lang|ine-x-proto|g}}'''<sup>..Ch</sup>;<br /> '''{{lang|ine-x-proto|j}}'''<sup>E..Ch</sup>
| rowspan="3"|'''{{lang|ine-x-proto|g}}''';<br />'''{{lang|ine-x-proto|ž}}'''<sup>E</sup> {{IPA|[ʒ]}};<br />'''{{lang|ine-x-proto|dz}}'''<sup>E'</sup>
| rowspan="3"|'''{{lang|ine-x-proto|g}}'''
|- align=center
!rowspan=2|'''{{lang|ine-x-proto|gʷʰ}}'''
|rowspan=2|'''{{lang|ine-x-proto|ph}}''';<br />'''{{lang|ine-x-proto|th}}'''<sup>E</sup>;<br />'''{{lang|ine-x-proto|kh}}'''<sup>(u)</sup>;<br /> '''{{lang|ine-x-proto|p}}'''<sup>..Ch</sup>;<br />'''{{lang|ine-x-proto|t}}'''<sup>E..Ch</sup>;<br />'''{{lang|ine-x-proto|k}}'''<sup>(u)..Ch</sup>
|rowspan=2|'''{{lang|ine-x-proto|f}}'''-;<br />'''{{lang|ine-x-proto|g}}''' /<br />-'''{{lang|ine-x-proto|u}}'''- {{IPA|[w]}};<br /><sup>n</sup>'''{{lang|ine-x-proto|gu}}''' {{IPA|[ɡʷ]}}
|rowspan=2|'''{{lang|ine-x-proto|g}}''';<br />'''{{lang|ine-x-proto|b}}'''-;<br />-'''{{lang|ine-x-proto|w}}'''-;<br /><sup>n</sup>'''{{lang|ine-x-proto|gw}}'''
|rowspan=2|'''{{lang|ine-x-proto|g}}''';<br />'''{{lang|ine-x-proto|b}}'''-;<br />-'''{{lang|ine-x-proto|w}}'''-
| ''*sneigʷʰ-'' || ''snow'' || ''sneha-'' || ''nípha'' || ''nivis'' || ''sniẽgas''
|barf
|- align=center
| ''*gʷʰerm-'' || ??''warm'' || ''gharmáḥ'' || ''thermós'' || ''formus'' || [[Latvian language|Latv.]] ''gar̂me''
|garm
|- align=center
! rowspan="2"|'''{{lang|ine-x-proto|s}}'''
| colspan="3"|'''{{lang|ine-x-proto|s}}'''
| rowspan="2"|'''{{lang|ine-x-proto|h}}'''-;<br />-'''{{lang|ine-x-proto|s}}''';<br />'''{{lang|ine-x-proto|s}}'''<sup>(T)</sup>;<br />-'''{{lang|ine-x-proto|Ø}}'''-;<br />{{IPA|[¯]}}<sup>(R)</sup>
| rowspan="2"|'''{{lang|ine-x-proto|s}}''';<br />-'''{{lang|ine-x-proto|r}}'''-
| rowspan="2"|'''{{lang|ine-x-proto|s}}''' {{IPA|[s]}};<br />-{{IPA|[h]}}-
| rowspan="2"|'''{{lang|ine-x-proto|s}}''';<br />`-'''{{lang|ine-x-proto|z}}'''-
| rowspan="2"|'''{{lang|ine-x-proto|s}}''';<br />`-'''{{lang|ine-x-proto|r}}'''-
| ''*septḿ̥'' || ''seven'' || ''saptá'' || ''heptá'' || ''septem'' || ''septynì''
|haft
|- align=center
|'''{{lang|ine-x-proto|ṣ}}'''<sup>ruki-</sup> {{IPA|[ʂ]}}
|'''{{lang|ine-x-proto|x}}'''<sup>ruki-</sup> {{IPA|[x]}}
|'''{{lang|ine-x-proto|š}}'''<sup>ruki-</sup> {{IPA|[ʃ]}}
| ''*h₂eusōs''<br />"dawn" || ''east'' || ''uṣā́ḥ'' || ''āṓs'' || ''aurōra'' || ''aušra''
|b''á''xtar
|- align=center
! '''{{lang|ine-x-proto|m}}'''
| colspan="5"|'''{{lang|ine-x-proto|m}}'''
| '''{{lang|ine-x-proto|m}}''' {{IPA|[m]}};<br />-{{IPA|[w̃]}}-
| colspan="2"|'''{{lang|ine-x-proto|m}}'''
| ''*mūs'' || ''mouse'' || ''mū́ṣ-'' || ''mũs'' || ''mūs'' || [[Old Church Slavonic|OCS]] ''myšĭ''
|mu''š''
|- align=center
! '''{{lang|ine-x-proto|-m}}'''
| -'''{{lang|ine-x-proto|m}}'''
| -'''{{lang|ine-x-proto|˛}}''' {{IPA|[˜]}}
| colspan="2"| -'''{{lang|ine-x-proto|n}}'''
| -'''{{lang|ine-x-proto|m}}'''
| -'''{{lang|ine-x-proto|n}}'''
| colspan="2"| -'''{{lang|ine-x-proto|Ø}}'''
| ''*ḱm̥tóm'' || ''hund(red)'' || ''śatám'' || ''(he)katón'' || ''centum'' || [[Old Prussian|OPrus]] ''simtan''
|sad
|- align=center
! '''{{lang|ine-x-proto|n}}'''
|'''{{lang|ine-x-proto|n}}'''
|'''{{lang|ine-x-proto|n}}''';<br />-'''{{lang|ine-x-proto|˛}}''' {{IPA|[˜]}}
| colspan="6"|'''{{lang|ine-x-proto|n}}'''
| ''*nokʷt-'' || ''night'' || ''nákt-'' || ''núkt-'' || ''noct-'' || ''naktis''
|n''áštá''
|- align=center
! '''{{lang|ine-x-proto|l}}'''
|'''{{lang|ine-x-proto|r}}''' (dial. '''{{lang|ine-x-proto|l}}''')
| colspan="7"|'''{{lang|ine-x-proto|l}}'''
| ''*leuk-'' || ''light'' || ''ruc-'' || ''leukós'' || ''lūx'' || ''laũkas''
|ruz
|- align=center
! '''{{lang|ine-x-proto|r}}'''
| colspan="8"|'''{{lang|ine-x-proto|r}}'''
| ''*h₁reudʰ-'' || ''red'' || ''rudhirá-'' || ''eruthrós'' || ''ruber'' || ''raũdas''
|sorx
|- align=center
! '''{{lang|ine-x-proto|i̯}}'''
| '''{{lang|ine-x-proto|y}}''' {{IPA|[j]}}
| colspan="2"|'''{{lang|ine-x-proto|j}}''' {{IPA|[j]}}
|'''{{lang|ine-x-proto|z}}''' {{IPA|[dz > zd, z]}} /<br />'''{{lang|ine-x-proto|h}}''';<br />-'''{{lang|ine-x-proto|Ø}}'''-
|'''{{lang|ine-x-proto|i}}''' {{IPA|[j]}};<br />-'''{{lang|ine-x-proto|Ø}}'''-
|'''{{lang|ine-x-proto|Ø}}'''
|'''{{lang|ine-x-proto|j}}'''
|'''{{lang|ine-x-proto|y}}'''
|''*yugóm'' || ''yoke'' || ''yugám'' || ''zugón'' || ''iugum'' || ''jùngas''
|yugh
|- align=center
! '''{{lang|ine-x-proto|u̯}}'''
|'''{{lang|ine-x-proto|v}}''' {{IPA|[ʋ]}}
|'''{{lang|ine-x-proto|v}}'''
|'''{{lang|ine-x-proto|v}}''' {{IPA|[ʋ]}}
|'''{{lang|ine-x-proto|w > h / Ø}}'''
|'''{{lang|ine-x-proto|u}}''' {{IPA|[w > v]}}
|'''{{lang|ine-x-proto|f}}''';<br />-'''{{lang|ine-x-proto|Ø}}'''-
| colspan="2"|'''{{lang|ine-x-proto|w}}'''
|''*h₂weh₁n̥to-'' || ''wind'' || ''vā́taḥ'' || ''áenta'' || ''ventus'' || ''vėtra''
|b''ád''
|-
! PIE !! [[Sanskrit|Skr.]] !! [[Old Church Slavonic|O.C.S.]] !! [[Lithuanian language|Lith.]] !! [[Greek language|Greek]] !! [[Latin]] !! [[Old Irish]] !! [[Gothic language|Gothic]] !! English
|}
</div>
:Notes:
* '''C'''- At the beginning of a word.
* -'''C'''- Between vowels.
* -'''C''' At the end of a word.
* `-'''C'''- Following an unstressed vowel ([[Verner's law]]).
* -'''C'''-<sup>(rl)</sup> Between vowels, or between a vowel and '''{{lang|ine-x-proto|r, l}}''' (on either side).
* '''C'''<sup>T</sup> Before a (PIE) stop ('''{{lang|ine-x-proto|p, t, k}}''').
* '''C'''<sup>T−</sup> After a (PIE) obstruent ('''{{lang|ine-x-proto|p, t, k}}''', etc.; '''{{lang|ine-x-proto|s}}''').
* '''C'''<sup>(T)</sup> Before or after an obstruent ('''{{lang|ine-x-proto|p, t, k}}''', etc.; '''{{lang|ine-x-proto|s}}''').
* '''C'''<sup>H</sup> Before an original laryngeal.
* '''C'''<sup>E</sup> Before a (PIE) front vowel ('''{{lang|ine-x-proto|i, e}}''').
* '''C'''<sup>E'</sup> Before secondary (post-PIE) front-vowels.
* '''C'''<sup>e</sup> Before '''{{lang|ine-x-proto|e}}'''.
* '''C'''<sup>(u)</sup> Before or after a (PIE) '''{{lang|ine-x-proto|u}}''' ([[boukólos rule]]).
* '''C'''<sup>(O)</sup> Before or after a (PIE) '''{{lang|ine-x-proto|o, u}}''' ([[boukólos rule]]).
* '''C'''<sup>n−</sup> After '''{{lang|ine-x-proto|n}}'''.
* '''C'''<sup>R</sup> Before a [[sonorant]] ('''{{lang|ine-x-proto|r, l, m, n}}''').
* '''C'''<sup>(R)</sup> Before or after a [[sonorant]] ('''{{lang|ine-x-proto|r, l, m, n}}''').
* '''C'''<sup>(r),l,u−</sup> Before '''{{lang|ine-x-proto|r, l}}''' or after '''{{lang|ine-x-proto|r, u}}'''.
* '''C'''<sup>ruki−</sup> After '''{{lang|ine-x-proto|r, u, k, i}}''' ([[Ruki sound law]]).
* '''C'''<sup>..Ch</sup> Before an aspirated consonant in the next syllable ([[Grassmann's law]], also known as [[dissimilation of aspirates]]).
* '''C'''<sup>E..Ch</sup> Before a (PIE) front vowel ('''{{lang|ine-x-proto|i, e}}''') as well as before an aspirated consonant in the next syllable ([[Grassmann's law]], also known as [[dissimilation of aspirates]]).
* '''C'''<sup>(u)..Ch</sup> Before or after a (PIE) '''{{lang|ine-x-proto|u}}''' as well as before an aspirated consonant in the next syllable ([[Grassmann's law]], also known as [[dissimilation of aspirates]]).

=== Comparison of conjugations ===

The following table presents a comparison of conjugations of the [[vowel stems|thematic]] [[present indicative]] of the verbal root {{lang|ine-x-proto|bʰer-}} of the English verb ''[[wikt:bear|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.

{| class="wikitable" style="text-align: center;"
|+
|-
!
! [[Proto-Indo-European]]<br /> ({{lang|ine-x-proto|[[wikt:Reconstruction:Proto-Indo-European/bʰer-|bʰer-]]}} 'to carry, to bear')
|-
! I (1st sg.)
| {{lang|ine-x-proto|bʰéroh₂}}
|-
! You (2nd sg.)
| {{lang|ine-x-proto|bʰéresi}}
|-
! He/She/It (3rd sg.)
| {{lang|ine-x-proto|bʰéreti}}
|-
! We two (1st [[Dual (grammatical number)|dual]])
| {{lang|ine-x-proto|bʰérowos}}
|-
! You two (2nd dual)
| {{lang|ine-x-proto|bʰéreth₁es}}
|-
! They two (3rd dual)
| {{lang|ine-x-proto|bʰéretes}}
|-
! We (1st pl.)
| {{lang|ine-x-proto|bʰéromos}}
|-
! You (2nd pl.)
| {{lang|ine-x-proto|bʰérete}}
|-
! They (3rd pl.)
| {{lang|ine-x-proto|bʰéronti}}
|}<!-- Indo-Iranian -->
<!-- Balto-Slavic -->{| class="wikitable" style="text-align: center;"
|-
! rowspan="2" | Major subgroup
! rowspan="2" |[[Hellenic languages|Hellenic]]
! colspan="2" |[[Indo-Iranian languages|Indo-Iranian]]
! rowspan="2" |[[Italic languages|Italic]]
! rowspan="2" |[[Celtic languages|Celtic]]
! rowspan="2" |[[Armenian languages|Armenian]]
! rowspan="2" |[[Germanic languages|Germanic]]
! colspan="2" |[[Balto-Slavic]]
! rowspan="2" |[[Albanian languages|Albanian]]
|-
![[Indo-Aryan languages|Indo-Aryan]]
![[Iranian languages|Iranian]]
![[Baltic languages|Baltic]]
![[Slavic languages|Slavic]]
|-
! Ancient representative
![[Ancient Greek]]
![[Vedic Sanskrit]]
![[Avestan]]
![[Latin]]
![[Old Irish]]
![[Classical Armenian]]
![[Gothic language|Gothic]]
![[Old Prussian]]
![[Old Church Slavic|Old Church Sl.]]
![[Old Albanian]]
|-
! I (1st sg.)
|[[wikt:φέρω|phérō]]
| bʰárāmi
| barāmi
|[[wikt:fero#Latin|ferō]]
| biru; berim
| berem
| baíra {{nobreak|/bɛra/}}
| *bera
| berǫ
| *berja
|-
! You (2nd sg.)
| phéreis
| bʰárasi
| barahi
| fers
| biri; berir
| beres
| baíris
| *bera
| bereši
| *berje
|-
! He/She/It (3rd sg.)
| phérei
| bʰárati
| baraiti
| fert
| berid
| berē
| baíriþ
| *bera
| beretъ
| *berjet
|-
! We two (1st dual)
| —
| bʰárāvas
| barāvahi
| —
| —
| —
| baíros
|—
| berevě
|—
|-
! You two (2nd dual)
| phéreton
| bʰárathas
| —
| —
| —
| —
| baírats
|—
| bereta
|—
|-
! They two (3rd dual)
| phéreton
| bʰáratas
| baratō
| —
| —
| —
| —
|—
| berete
|—
|-
! We (1st pl.)
| phéromen
| bʰárāmas
| barāmahi
| ferimus
| bermai
| beremkʿ
| baíram
| *beramai
| beremъ
| *berjame
|-
! You (2nd pl.)
| phérete
| bʰáratha
| baraθa
| fertis
| beirthe
| berēkʿ
| baíriþ
| *beratei
| berete
| *berjeju
|-
! They (3rd pl.)
| phérousi
| bʰáranti
| barəṇti
| ferunt
| berait
| beren
| baírand
| *bera
| berǫtъ
| *berjanti
|-
! Modern representative
![[Modern Greek]]
![[Hindustani language|Hindustani]]
![[Persian language|Persian]]
![[Portuguese language|Portuguese]]
![[Irish language|Irish]]
![[Armenian language|Armenian (Eastern; Western)]]
![[German language|German]]
![[Lithuanian language|Lithuanian]]
![[Slovene language|Slovene]]
![[Albanian language|Albanian]]
|-
! I (1st sg.)
| férno
| (ma͠i) bʰarūm̥
| (man) {mi}baram
| {con}firo
|[[wikt:beir#Irish|beirim]]
| berum em; g'perem
| (ich) {ge}bäre
| beriu
| bérem
| (unë) bie
|-
! You (2nd sg.)
| férnis
| (tū) bʰarē
| (tu) {mi}bari
| {con}feres
| beirir
| berum es; g'peres
| (du) {ge}bierst
| beri
| béreš
| (ti) bie
|-
! He/She/It (3rd sg.)
| férni
| (ye/vo) bʰarē
| (ān) {mi}barad
| {con}fere
| beiridh
| berum ē; g'perē
| (er/sie/es) {ge}biert
| beria
| bére
| (ai/ajo) bie
|-
! We two (1st dual)
|—
|—
|—
|—
|—
|—
|—
| beriava
| béreva
|—
|-
! You two (2nd dual)
|—
|—
|—
|—
|—
|—
|—
|beriata
|béreta
|—
|-
! They two (3rd dual)
|—
|—
|—
|—
|—
|—
|—
| beria
| béreta
|—
|-
! We (1st pl.)
| férnume
| (ham) bʰarēm̥
| (mā) {mi}barim
| {con}ferimos
| beirimid; beiream
| berum enkʿ; g'perenkʿ
| (wir) {ge}bären
| beriame
| béremo
| (ne) biem
|-
! You (2nd pl.)
| férnete
| (tum) bʰaro
| (šomā) {mi}barid
| {con}feris
| beirthidh
| berum ekʿ; g'perekʿ
| (ihr) {ge}bärt
| beriate
| bérete
| (ju) bini
|-
! They (3rd pl.)
| férnun
| (ye/vo) bʰarēm̥
| (ānān) {mi}barand
| {con}ferem
| beirid
| berum en; g'peren
| (sie) {ge}bären
| beria
| bérejo; berọ́
| (ata/ato) bien
|}

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 language|synthetic]] verb systems to largely [[periphrastic]] systems. In addition, the [[pronoun]]s of periphrastic forms are in parentheses when they appear. Some of these verbs have undergone a change in meaning as well.
* In [[Modern Irish]] ''beir'' 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 [[periphrasis|periphrastically]] by adding a pronoun after the verb: ''beireann tú, beireann sé/sí, beireann sibh, beireann siad''.
* The [[Hindustani grammar|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 [[Subjunctive mood|future subjunctive]].<ref name=":1">{{Cite journal |last=van Olphen |first=Herman |date=1975 |title=Aspect, Tense, and Mood in the Hindi Verb |journal=Indo-Iranian Journal |volume=16 |issue=4 |pages=284–301 |doi=10.1163/000000075791615397 |jstor=24651488 |s2cid=161530848 |issn=0019-7246 |url=http://www.jstor.org/stable/24651488 |url-access=subscription}}</ref> The loss of the [[present indicative]] in Hindustani is roughly compensated by the periphrastic [[Habitual aspect|habitual indicative]] construction, using the [[Habitual aspect|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 {{Circa|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 {{lang|pt|sofrer}} "to suffer" (from Latin ''sub-'' and ''ferre'') and {{lang|pt|conferir}} "to confer" (from Latin ''con-'' and ''ferre'').
* In Modern [[Greek language|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 now used only in some dialects (e.g. [[Samogitian dialect|Samogitian]]).
* Among modern Slavic languages, only Slovene continues to have a dual number in the standard variety.

== Comparison of cognates ==
{{Main|Indo-European vocabulary}}
{{See also|Proto-Indo-European numerals}}

== Present distribution ==
{{See also|List of Indo-European languages}}
[[File:Indo-European distribution.svg|thumb|upright=1.55|
{{legend|#045a8d|An Indo-European language is the majority native language
}}
{{legend|#0674b6|An Indo-European language is a co-official and majority native language}}
{{legend|#439dd4|An Indo-European language is an official but minority native language}}
{{legend|#9bbae1 |An Indo-European language is a cultural or secondary language}}
{{legend|#c0c0c0|An Indo-European language is not widely spoken}}]]
[[File:Americaslanguages (orthographic projection)-2.png|thumb|upright=1.27|Distribution of Indo-European languages in the [[Americas]]
<br />
[[romance languages|Romance]]:
{{Legend|#4CC200|[[Spanish language|Spanish]]}}
{{Legend|#FF8800|[[Portuguese language|Portuguese]]}}
{{Legend|#00269F|[[French language|French]]}}
[[Germanic languages|Germanic]]:
{{Legend|#CD0000|[[English language|English]]}}
{{Legend|#FFD800|[[Dutch language|Dutch]]}}
]]

Today, Indo-European languages are spoken by billions of [[Native speaker#Defining "native speaker"|native speakers]] across all inhabited continents,<ref>{{cite web |title=Ethnologue list of language families |publisher=[[Ethnologue]] |edition=22nd |date=25 May 2019 |access-date=2 July 2019 |url=http://www.ethnologue.com/ethno_docs/distribution.asp?by=family |url-access=subscription}}</ref> the largest number by far for any recognized language family. Of the [[List of languages by total number of speakers|20 languages with the largest numbers of speakers]] according to ''Ethnologue'', 10 are Indo-European: [[English language|English]], [[Hindustani language|Hindustani]], [[Spanish language|Spanish]], [[Bengali language|Bengali]], [[French language|French]], [[Russian language|Russian]], [[Portuguese language|Portuguese]], [[German language|German]], [[Persian language|Persian]] and [[Punjabi language|Punjabi]], each with 100&nbsp;million speakers or more.<ref>{{cite web |title=Ethnologue list of languages by number of speakers |date=3 October 2018 |publisher=[[Ethnologue]] |access-date=29 July 2021 |url=http://www.ethnologue.com/ethno_docs/distribution.asp?by=size |url-access=subscription}}</ref> Additionally, hundreds of millions of persons worldwide study Indo-European languages as secondary or tertiary languages, including in cultures which have completely different language families and historical backgrounds—there are around 600 million<ref>{{cite web |title=English |publisher=[[Ethnologue]] |access-date=17 January 2017 |url=https://www.ethnologue.com/language/eng |url-access=subscription}}</ref><!-- and one&nbsp;billion<ref>{{cite web |url=http://blog.oxforddictionaries.com/2015/08/ten-things-you-might-not-have-known-about-the-english-language/ |archive-url=https://web.archive.org/web/20150813233120/http://blog.oxforddictionaries.com/2015/08/ten-things-you-might-not-have-known-about-the-english-language/ |url-status=dead |archive-date=13 August 2015 |title=Ten Things You Might Not Have Known About the English Language |publisher=[[Oxford Dictionaries (website)|Oxford Dictionaries]] |date=12 August 2015}}</ref> L2--> learners of English alone.

The success of the language family, including the large number of speakers and the vast portions of the Earth that they inhabit, is due to several factors. The ancient [[Indo-European migrations]] and widespread dissemination of [[Indo-European culture]] throughout [[Eurasia]], including that of the [[Proto-Indo-Europeans]] themselves, and that of their daughter cultures including the [[Indo-Aryan migration theory|Indo-Aryans]], [[Iranian peoples]], [[Celts]], [[Hellenistic period|Greeks]], [[Roman Empire|Romans]], [[Germanic peoples]], and [[Slavs]], led to these peoples' branches of the language family already taking a dominant foothold in virtually all of [[Eurasia]] except for swathes of the [[Near East]], [[North Asia|North]] and [[East Asia]], replacing many (but not all) of the previously-spoken [[pre-Indo-European languages]] of this extensive area. However [[Semitic languages]] remain dominant in much of the [[Middle East]] and [[North Africa]], and [[Caucasian languages]] in much of the [[Caucasus]] region. Similarly in [[Europe]] and the [[Urals]] the [[Uralic languages]] (such as Hungarian, Finnish, Estonian etc.) remain, as does [[Basque language|Basque]], a pre-Indo-European isolate.

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 languages|Semitic]], [[Dravidian languages|Dravidian]], [[Languages of the Caucasus|Caucasian]], and [[Uralic languages]], and the language isolate [[Basque language|Basque]] remained of the (relatively) [[Paleo-European languages|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 language|English]] continuing to lead the group; English in general has in many respects [[English as a lingua franca|become the ''lingua franca'']] of global communication.

{{Clear}}

== See also ==
{{Wiktionary|Appendix:Indo-European Swadesh lists}}
{{Commons category}}
* [https://en.wiktionary.org/wiki/Appendix:Indo-European_Swadesh_lists Indo-European Swadesh lists]

{{col div|colwidth=20em}}
* [[Grammatical conjugation]]
* ''[[The Horse, the Wheel, and Language]]'' (book)
* [[Indo-European copula]]
* [[Indo-European sound laws]]
* [[Indo-European studies]]
* [[Indo-Semitic languages]]
* [[Indo-Uralic languages]]
* [[Eurasiatic languages]]
* [[Language family]]
* [[Languages of Asia]]
* [[Languages of Europe]]
* [[Languages of India]]
* [[Linguistics]]
* [[List of Indo-European languages]]
* [[Proto-Indo-European root]]
* [[Proto-Indo-European religion]]
{{colend}}

== Notes ==
{{NoteFoot}}

== References ==
=== Citations ===
{{Reflist}}

=== Sources ===
{{sfn whitelist |CITEREFRinge2006}}
{{refbegin}}
* {{cite encyclopedia |author=AA. VV. |date=1981 |encyclopedia=Encyclopædia Britannica |title=Indo-European languages |volume=22 |edition=15th |publisher=Helen Hemingway Benton |location=Chicago |ref=CITEREFEncyclopædia Britannica1981}}
* {{cite book |last=Anthony |first=David W. |title=The Horse, the Wheel, and Language: How Bronze-Age Riders from the Eurasian Steppes Shaped the Modern World |publisher=Princeton University Press |url=https://www.google.com/books/edition/The_Horse_the_Wheel_and_Language/0FDqf415wqgC?hl=en&gbpv=1&dq=isbn:9781400831104&printsec=frontcover |year=2007 |ref=HWL |isbn=978-0-691-05887-0}}
* {{cite book |last=Auroux |first=Sylvain |title=History of the Language Sciences |publisher=Walter de Gruyter |location=Berlin |date=2000 |isbn=978-3-11-016735-1 |url=https://books.google.com/books?id=yasNy365EywC&q=3110167352&pg=PA1156}}
* {{cite book |last=Beekes |first=Robert S. P. |author-link=Robert S. P. Beekes |date=1995 |translator-last1=Vertalers |translator-first1=Uva |translator-last2=Gabriner |translator-first2=Paul |title=Comparative Indo-European Linguistics: An Introduction |edition=1st |location=Amsterdam |publisher=John Benjamins |isbn=9027221510}}
* {{cite book |last=Beekes |first=Robert S. P. |author-link=Robert S. P. Beekes |others=Revised and corrected by [[Michiel de Vaan]] |date=2011 |title=Comparative Indo-European linguistics: An Introduction |edition=2nd |location=Amsterdam |publisher=John Benjamins |isbn=978-9027285003 |url=https://books.google.com/books?id=W-HXnIG75PYC}} Paperback: {{ISBN|978-9027211866}}.
* {{cite book |last=Brugmann |first=Karl |author-link=Karl Brugmann |date=1886 |title=Grundriss der Vergleichenden Grammatik der indogermanischen Sprachen |volume=Erster Band |location=Strassburg |publisher=Karl J. Trübner |language=de}}
* {{cite book |last=Collinge |first=N.E. |date=1985 |title=The Laws of Indo-European |location=Amsterdam |publisher=John Benjamins |isbn=9789027235305 |url=https://archive.org/details/lawsofindoeurope0000coll |url-access=registration}}
* {{cite book |last=Fortson |first=Benjamin W. |authorlink=Benjamin W. Fortson IV |title=Indo-European Language and Culture: An Introduction |location=Malden, Massachusetts |publisher=Blackwell |year=2004 |isbn=978-1-4051-0315-2}}
* {{cite book |last=Hamp |first=Eric |date=2007 |title=Studime krahasuese për shqipen |trans-title=Comparative studies on Albanian |editor=Rexhep Ismajli |publisher=Akademia e Shkencave dhe e Arteve e Kosovës, Prishtinë |language=sq}}
* {{cite book |last=Holm |first=Hans J. |date=2008 |chapter=The Distribution of Data in Word Lists and its Impact on the Subgrouping of Languages |chapter-url=http://www.hjholm.de/ |editor1-last=Preisach |editor1-first=Christine |editor2-last=Burkhardt |editor2-first=Hans |editor3-last=Schmidt-Thieme |editor3-first=Lars |editor4-last=Decker |editor4-first=Reinhold |display-editors=3 |title=Data analysis, machine learning and applications |series=Proceedings of the 31st Annual Conference of the German Classification Society (GfKl), University of Freiburg, 7–9 March 2007 |location=Heidelberg |publisher=Springer-Verlag |isbn=978-3-540-78239-1 |url=https://archive.org/details/springer_10.1007-978-3-540-78246-9}}
* {{cite journal |last=Kortlandt |first=Frederik |authorlink=Frederik Kortlandt |date=1988 |title=The Thraco-Armenian consonant shift |journal=Linguistique Balkanique |volume=31 |pages=71–74}}
* {{cite journal |last=Kortlandt |first=Frederik |date=1990 |orig-date=1989 |title=The Spread of the Indo-Europeans |journal=Journal of Indo-European Studies |volume=18 |issue=1–2 |pages=131–140 |url=http://www.kortlandt.nl/publications/art111e.pdf}}
* {{cite journal |last=Lubotsky |first=Alexander |authorlink=Alexander Lubotsky|date=1988 |title=The Old Phrygian Areyastis-inscription |journal=Kadmos |volume=27 |pages=9–26 |doi=10.1515/kadmos-1988-0103 |hdl=1887/2660 |s2cid=162944161 |hdl-access=free |url=https://openaccess.leidenuniv.nl/bitstream/handle/1887/2660/299_011.pdf}}
* {{cite book |last=Porzig |first=Walter |date=1954 |title=Die Gliederung des indogermanischen Sprachgebiets |publisher=Carl Winter Universitätsverlag |location=Heidelberg}}
* {{cite book |last=Renfrew |first=C. |author-link=Colin Renfrew |date=2001 |chapter=The Anatolian origins of Proto-Indo-European and the autochthony of the Hittites |editor-first=R. |editor-last=Drews |editor-link=Robert Drews |title=Greater Anatolia and the Indo-Hittite language family |location=Washington, DC |publisher=Institute for the Study of Man |isbn=978-0-941694-77-3}}
* {{cite Q |Q131605459 |first=Don |last=Ringe |author-link=Donald Ringe |url=https://archive.org/details/anglosaxondictionary_202001/From%20Proto-Indo-European%20to%20Proto-Germanic/mode/2up |mode=cs1}}
* {{cite book |last=Schleicher |first=August |author-link=August Schleicher |date=1861 |title=Compendium der vergleichenden Grammatik der indogermanischen Sprachen |location=Weimar |publisher=Böhlau (reprinted by Minerva GmbH, Wissenschaftlicher Verlag) |isbn=978-3-8102-1071-5 |language=de}}
* {{cite book |last=Schleicher |first=August |author-link=August Schleicher |date=1874–1877 |translator-first=Herbert |translator-last=Bendall |title=A Compendium of the Comparative Grammar of the Indo-European, Sanskrit, Greek and Latin languages |series=Part I and Part II |location=London |publisher=Trübner & Co. |url=https://archive.org/details/in.ernet.dli.2015.13063/page/n2 |url-access=registration}} [https://archive.org/details/acompendiumcomp00schlgoog/page/n8 Part II via Internet Archive].
* {{cite journal |last=Szemerényi |first=Oswald John Louis |author-link=Oswald Szemerényi |date=1957 |title=The Problem of Balto-Slav Unity: A Critical Survey |journal=Kratylos |volume=2 |pages=97–123 |publisher=O. Harrassowitz}}
** Reprinted in {{cite book |last1=Szemerényi |first1=Oswald John Louis |date=1991 |title=Scripta Minora: Selected Essays in Indo-European, Greek, and Latin |volume=IV: Indo-European Languages other than Latin and Greek |publisher=Institut für Sprachwissenschaft der Universität Innsbruck |series=Innsbrucker Beiträge zur Sprachwissenschaft |editor1-first=P. |editor1-last=Considine |editor2-first=James T. |editor2-last=Hooker |isbn=978-3-85124-611-7 |issn=1816-3920 |pages=2145–2171}}
* {{cite book |last1=Szemerényi |first1=Oswald John Louis |author-link=Oswald Szemerényi |first2=David |last2=Jones |first3=Irene |last3=Jones |date=1999 |title=Introduction to Indo-European Linguistics |publisher=Oxford University Press |isbn=978-0-19-823870-6}}
* {{cite book |title=Über Methode und Ergebnisse der arischen (indogermanischen) Alterthumswissenshaft |first=Peter |last=von Bradke |language=de |date=1890 |location=Giessen |publisher=J. Ricker'che Buchhandlung}}
{{refend}}

== Further reading ==
* {{cite journal |last=Bjørn |first=Rasmus G. |title=Indo-European Loanwords and Exchange in Bronze Age Central and East Asia |journal=Evolutionary Human Sciences |date=2022 |volume=4 |pages=e23 |doi=10.1017/ehs.2022.16 |pmid=37599704 |pmc=10432883 |s2cid=248358873 |doi-access=free}}
* {{cite book |author-link=Byomkes Chakrabarti |last=Chakrabarti |first=Byomkes |date=1994 |title=A Comparative Study of Santali and Bengali |location=Calcutta |publisher=K. P. Bagchi & Co. |isbn=978-81-7074-128-2}}
* {{cite book |author-link=Pierre Chantraine |last=Chantraine |first=Pierre |date=1968 |url=https://archive.org/details/Dictionnaire-Etymologique-Grec |title=Dictionnaire étymologique de la langue grecque |url-access=registration |via=Internet Archive |location=Paris |publisher=Klincksieck}}
* {{Cite book |title=The Kurgan Culture and The Indo-Europeanization of Europe |last=Gimbutas |first=Marija |date=1997 |isbn=0-941694-56-9 |url=https://www.jies.org/DOCS/monojpgs/Mon18.html |editor-last=Robbins Dexter |editor-first=Miriam |series=JIES Monograph |volume=18 |author-link=Marija Gimbutas |editor-last2=Jones-Bley |editor-first2=Karlene}}
* {{Cite book |title=Talking Neolithic: Proceedings of the Workshop on Indo-European Origins held at the Max Planck Institute for Evolutionary Anthropology, Leipzig, December 2–3, 2013 |date=2018 |isbn=978-0-9983669-2-0 |url=https://www.jies.org/DOCS/monojpgs/Mon65.html |editor-last=Kroonen |editor-first=Guus |series=JIES Monograph |volume=65 |editor-last2=Mallory |editor-first2=James P. |editor-last3=Comrie |editor-first3=Bernard}}
* {{cite book |author-link=J. P. Mallory |last=Mallory |first=J. P. |date=1989 |title=In Search of the Indo-Europeans |url=https://archive.org/details/insearchofindoeu00jpma |via=Internet Archive |url-access=registration |location=London |publisher=Thames and Hudson |isbn=978-0-500-27616-7}}
* {{Cite book |title=Revisiting Dispersions Celtic and Germanic ca. 400 BC–ca. 400 AD Proceedings of the International Interdisciplinary Conference held at Dolenjski muzej, Novo mesto, Slovenia; October 12th–14th, 2018 |date=2020 |isbn=978-0-9845353-7-8 |url=https://www.jies.org/DOCS/monojpgs/Mon67.html |editor-last=Markey |editor-first=T. L. |series=JIES Monograph |volume=67 |editor-last2=Repanšek |editor-first2=Luka}}
* {{cite book |author-link=Antoine Meillet |last=Meillet |first=Antoine |title=Esquisse d'une grammaire comparée de l'arménien classique |date=1936 |edition=2nd |url=https://archive.org/details/esquissedunegram0000meil |url-access=registration |via=Internet Archive |publisher=[[Mekhitarist Monastery, Vienna|Mekhitarist Monastery]] |location=Vienna}}
* {{cite book |editor1-last=Olander |editor1-first=Thomas |title=The Indo-European Language Family: A Phylogenetic Perspective |date=September 2022 |doi=10.1017/9781108758666 |publisher=Cambridge University Press |isbn=978-1-108-75866-6 |s2cid=161016819 |s2cid-access=free}}
* {{cite book |editor-last1=Ramat |editor-first1=Paolo |editor-last2=Giacalone Ramat |editor-first2=Anna |date=1998 |title=The Indo-European Languages |location=London |isbn=0-415-06449-X |publisher=Routledge}}
* {{cite journal |last=Remys |first=Edmund |title=General distinguishing features of various Indo-European languages and their relationship to Lithuanian |journal=Indogermanische Forschungen |issn=0019-7262 |volume=112 |date=17 December 2007 |issue=2007 |pages=244–276 |doi=10.1515/9783110192858.1.244 |isbn=978-3-11-019285-8 |s2cid=169996117}}
* {{cite book |editor1-last=Strazny |editor1-first=Philip |editor2-last=Trask |editor2-first=R. L. |editor2-link=Larry Trask |date=2000 |title=Dictionary of Historical and Comparative Linguistics |publisher=Routledge |edition=1st |isbn=978-1-57958-218-0}}
* {{cite book |last=Watkins |first=Calvert |author-link=Calvert Watkins |title=The American Heritage Dictionary of Indo-European Roots |publisher=Houghton Mifflin |date=2000 |isbn=978-0-618-08250-6}}
* Asadpour, Hiwa, and Thomas Jügel, eds. Word Order Variation: Semitic, Turkic and Indo-European Languages in Contact. Vol. 31. Walter de Gruyter GmbH & Co KG, 2022.

== External links ==
{{Commons category|Indo-European languages}}
{{EB1911 poster|Indo-European Languages}}
{{Library resources box |by=no |onlinebooks=yes |others=yes |about=yes |label=Indo-European languages
 |viaf= |lccn= |lcheading= |wikititle= }}
* [https://archive.org/details/EncyclopediaOfIndoEuropeanCulture/mode/2up Encyclopedia of Indo-European Culture (1997)]

=== Databases ===
* {{cite web |title=Comparative Indo-European |url=http://www.wordgumbo.com/ie/cmp/ |first1=Isidore |last1=Dyen |first2=Joseph |last2=Kruskal |first3=Paul |last3=Black |date=1997 |access-date=13 December 2009 |publisher=wordgumbo |archive-date=22 May 2010 |archive-url=https://web.archive.org/web/20100522002324/http://www.wordgumbo.com/ie/cmp/ |url-status=dead }}
* {{cite web |title=Indo-European |url=http://languageserver.uni-graz.at/ls/group?id=4 |publisher=LLOW Languages of the World |access-date=14 December 2009 |archive-date=10 October 2017 |archive-url=https://web.archive.org/web/20171010183735/http://languageserver.uni-graz.at/ls/group?id=4 |url-status=dead}}
* {{cite web |title=Indo-European Documentation Center |url=http://www.utexas.edu/cola/centers/lrc/iedocctr/ie.html |publisher=Linguistics Research Center, [[University of Texas at Austin]] |date=2009 |access-date=14 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090903062241/http://www.utexas.edu/cola/centers/lrc/iedocctr/ie.html |archive-date=3 September 2009}}
* {{Cite book |editor-last=Lewis |editor-first=M. Paul |date=2009 |title=Ethnologue: Languages of the World, Online version |edition=16th |location=Dallas |publisher=SIL International |contribution=Language Family Trees: Indo-European |url=http://www.ethnologue.com/show_family.asp?subid=2-16}}.
* {{cite web |title=Thesaurus Indogermanischer Text- und Sprachmaterialien: TITUS |url=http://titus.uni-frankfurt.de/indexe.htm |date=2003 |publisher=TITUS, University of Frankfurt |language=de |access-date=13 December 2009}}
* {{cite web |title=Indo-European Lexical Cognacy Database (IELex) |date=2021 |url=https://github.com/evotext/ielex-data-and-tree |publisher=Uppsala University}}
* [https://spw.uni-goettingen.de/projects/aig/index.html Glottothèque: Ancient Indo-European Grammars online], an online collection of introductory videos to Ancient Indo-European languages produced by the University of Göttingen

=== Lexica ===
* {{cite web |title=Indo-European Etymological Dictionary (IEED) |url=http://www.indoeuropean.nl |publisher=Department of Comparative Indo-European Linguistics, Leiden University |location=Leiden, Netherlands |access-date=14 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20060207135952/http://www.indoeuropean.nl/ |archive-date=7 February 2006}}
* {{cite book |title=The American Heritage Dictionary of the English Language |edition=4th |orig-year=2000 |chapter=Indo-European Roots Index |date=22 August 2008 |publisher=Internet Archive: Wayback Machine |chapter-url=http://www.bartleby.com/61/IEroots.html |access-date=9 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090217023123/http://bartleby.com/61/IEroots.html |archive-date=17 February 2009}}
* {{cite book |last=Köbler |first=Gerhard |title=Indogermanisches Wörterbuch |url=http://www.koeblergerhard.de/idgwbhin.html |edition=5th |date=2014 |publisher=Gerhard Köbler |language=de |access-date=29 March 2015}}
* {{cite web |last=Schalin |first=Johan |title=Lexicon of Early Indo-European Loanwords Preserved in Finnish |url=http://www.iki.fi/jschalin/?cat=10 |publisher=Johan Schalin |date=2009 |access-date=9 December 2009}}

{{Indo-European languages}}
{{Language families}}
{{Eurasian languages}}
{{Authority control}}

[[Category:Indo-European languages| ]]
[[Category:Language families]]