View source for Proto-Indo-European language

{{Short description|Ancestor of the Indo-European languages}}
{{redirect2|PIE|Proto-Indo-European|the people|Proto-Indo-Europeans|other uses|PIE (disambiguation)}}
{{Distinguish|Pre-Indo-European languages|Paleo-European languages}}
{{Infobox proto-language
| name        = Proto-Indo-European
| altname     = PIE
| region      = [[Proto-Indo-European homeland]], most likely on the {{nbr|[[Pontic–Caspian steppe]]}}
| era         = {{circa|4500|2500 BC}}
| familycolor = Indo-European
| target      = [[Indo-European languages]]
| child1      = [[Proto-Albanian language|Proto-Albanian]]
| child2      = [[Proto-Anatolian language|Proto-Anatolian]]
| child3      = [[Proto-Armenian language|Proto-Armenian]]
| child4      = [[Proto-Balto-Slavic language|Proto-Balto-Slavic]]
| child5      = [[Proto-Celtic language|Proto-Celtic]]
| child6      = [[Proto-Germanic language|Proto-Germanic]]
| child7      = [[Proto-Greek language|Proto-Greek]]
| child8      = [[Proto-Indo-Iranian language|Proto-Indo-Iranian]]
| child9      = [[Proto-Italic language|Proto-Italic]]
| child10     = [[Proto-Tocharian language|Proto-Tocharian]]
| listclass   = 
| boxsize     = 
| module      = 
| notes       = 
}}
{{Contains special characters|PIE}}
'''Proto-Indo-European''' ('''PIE''') is the reconstructed [[Proto-language|common ancestor]] of the [[Indo-European language family]].<ref>{{Cite encyclopedia|title=Indo-European languages |at=The parent language: Proto-Indo-European|url=https://www.britannica.com/topic/Indo-European-languages|access-date=2021-09-19|encyclopedia=Encyclopædia Britannica|language=en}}</ref> No direct record of Proto-Indo-European has been discovered; its proposed features have been derived by [[linguistic reconstruction]] from documented Indo-European languages. Far more work has gone into reconstructing PIE than any other [[proto-language]], and it is the best understood of all proto-languages of its age. The majority of linguistic work during the 19th century was devoted to the reconstruction of PIE and its [[daughter language]]s, and many of the modern techniques of linguistic reconstruction (such as the [[comparative method]]) were developed as a result.<ref>{{Cite encyclopedia |last1=Ivić |first1=Pavle |last2=Hamp |first2=Eric P. |last3=Lyons |first3=John |date=March 5, 2024 |title=Linguistics |url=https://www.britannica.com/science/linguistics/The-comparative-method |access-date=August 9, 2024 |encyclopedia=Encyclopædia Britannica}}</ref>

PIE is hypothesized to have been spoken as a single language from approximately 4500&nbsp;BCE to 2500&nbsp;BCE<ref>{{Cite magazine |url=https://archaeology.org/issues/september-october-2013/features/timber-grave-culture-krasnosamarskoe-bronze-age/ |title=Wolf Rites of Winter |date=September–October 2013 |magazine=Archaeology |last=Powell |first=Eric A. |access-date=2025-04-23 |issn=0003-8113}}</ref> during the Late [[Neolithic]] to Early [[Bronze Age]], though estimates vary by more than a thousand years. According to the prevailing [[Kurgan hypothesis]], the [[proto-Indo-European homeland|original homeland]] of the [[Proto-Indo-Europeans]] may have been in the [[Pontic–Caspian steppe]] of eastern Europe. The linguistic reconstruction of PIE has provided insight into the pastoral [[proto-Indo-European culture|culture]] and patriarchal [[proto-Indo-European religion|religion]] of its speakers.{{sfnp|Fortson|2010|p=16}} As speakers of Proto-Indo-European became isolated from each other through the [[Indo-European migrations]], the regional [[dialect]]s of Proto-Indo-European spoken by the various groups diverged, as each dialect underwent shifts in pronunciation (the [[Indo-European sound laws]]), morphology, and vocabulary. Over many centuries, these dialects transformed into the known ancient Indo-European languages. From there, further linguistic divergence led to the evolution of their current descendants, the modern Indo-European languages.

PIE is believed to have had an elaborate system of [[morphology (linguistics)|morphology]] that included [[inflection|inflectional suffixes]] (analogous to English ''child, child's, children, children's'') as well as [[Indo-European ablaut|ablaut]] (vowel alterations, as preserved in English ''sing, sang, sung, song'') and [[proto-Indo-European accent|accent]]. PIE [[proto-Indo-European nominals|nominals]] and [[proto-Indo-European pronouns|pronouns]] had a complex system of [[declension]], and [[Proto-Indo-European verbs|verbs]] similarly had a complex system of [[Grammatical conjugation|conjugation]]. The PIE [[proto-Indo-European phonology|phonology]], [[proto-Indo-European particles|particles]], [[proto-Indo-European numerals|numerals]], and [[indo-European copula|copula]] are also well-reconstructed. Asterisks are used by linguists as a conventional mark of reconstructed words, such as {{lang|ine-x-proto|wódr̥}}, {{lang|ine-x-proto|ḱwn̥tós}}, or {{lang|ine-x-proto|tréyes}}; these forms are the reconstructed ancestors of the modern English words ''water'', ''hound'', and ''three'', respectively.

==Development of the hypothesis==
{{Indo-European topics}}
No direct evidence of PIE exists; scholars have reconstructed PIE from its present-day descendants using the [[comparative method (linguistics)|comparative method]].<ref>{{cite web |url=https://www.britannica.com/science/linguistics/The-comparative-method#toc35116 |title=Linguistics – The comparative method |series=Science |publisher=Encyclopedia Britannica |access-date=27 July 2016}}</ref> For example, compare the pairs of words in Italian and English: {{lang|it|piede}} and ''foot'', {{lang|it|padre}} and ''father'', {{lang|it|pesce}} and ''fish''. Since there is a consistent correspondence of the initial consonants (''p'' and ''f'') that emerges far too frequently to be unrelated coincidence, one can infer that these languages stem from a common [[parent language]].<ref name="comp-ling">{{cite encyclopedia |title=Comparative linguistics |url=https://www.britannica.com/science/comparative-linguistics |encyclopedia=[[Encyclopædia Britannica]] |access-date=27 August 2016}}</ref> Detailed analysis suggests a system of [[Indo-European sound laws|sound laws]] to describe the [[phonetics|phonetic]] and [[Phonology|phonological]] changes from the hypothetical ancestral words to the modern ones. These laws have become so detailed and reliable as to support the [[Neogrammarian hypothesis]]: the Indo-European sound laws apply without exception.

[[William Jones (philologist)|William Jones]], an [[Anglo-Welsh]] [[Philology|philologist]] and [[puisne judge]] in [[Bengal]], caused an academic sensation when in 1786 he postulated the common ancestry of [[Sanskrit]], [[Greek language|Greek]], [[Latin]], [[Gothic language|Gothic]], the [[Celtic languages]], and [[Old Persian]],<ref>{{cite encyclopedia |url=https://www.britannica.com/biography/William-Jones-British-orientalist-and-jurist |title=Sir William Jones, British orientalist and jurist |encyclopedia=[[Encyclopædia Britannica]] |access-date=3 September 2016}}</ref> but he was not the first to state such a hypothesis. In the 16th century, European visitors to the [[Indian subcontinent]] became aware of similarities between [[Indo-Iranian language]]s and European languages,<ref name="auroux">{{cite book |first=Sylvain |last=Auroux |title=History of the Language Sciences |page=1156 |isbn=3-11-016735-2 |publisher=[[Walter de Gruyter]] |year=2000 |url=https://books.google.com/books?id=yasNy365EywC&q=3110167352&pg=PA1156}}</ref> and as early as 1653, [[Marcus Zuerius van Boxhorn]] had published a proposal for a [[proto-language]] ("Scythian") for the following language families: [[Germanic languages|Germanic]], [[Romance languages|Romance]], [[Hellenic languages|Greek]], [[Baltic languages|Baltic]], [[Slavic languages|Slavic]], [[Celtic languages|Celtic]], and [[Iranian languages|Iranian]].<ref name="Blench">{{cite book |author-link=Roger Blench |first=Roger |last=Blench |url=http://www.rogerblench.info/Archaeology/World/CH4-BLENCH.pdf |article=Archaeology and language: Methods and issues |title=A Companion to Archaeology |editor=Bintliff, J. |pages=52–74 |place=Oxford, UK |publisher=Basil Blackwell |year=2004}}</ref> In a memoir sent to the {{lang|fr|[[Académie des Inscriptions et Belles-Lettres]]|italic=no}} in 1767, {{lang|fr|[[Gaston-Laurent Coeurdoux]]|italic=no}}, a French [[Jesuit]] who spent most of his life in India, had specifically demonstrated the analogy between Sanskrit and European languages.<ref>{{cite web |first=Kip |last=Wheeler |title= The Sanskrit Connection: Keeping Up With the Joneses |url=http://web.cn.edu/kwheeler/IE_Main4_Sanskrit.html |publisher=[[Carson–Newman University]] |access-date=16 April 2013 }}</ref> According to current academic consensus, Jones's famous work of 1786 was less accurate than his predecessors', as he erroneously included [[Egyptian language|Egyptian]], [[Japanese language|Japanese]] and [[Chinese language|Chinese]] in the Indo-European languages, while omitting [[Hindi]].

In 1818, Danish linguist [[Rasmus Christian Rask]] elaborated the set of correspondences in his prize essay {{lang|da|Undersøgelse om det gamle Nordiske eller Islandske Sprogs Oprindelse}} ('Investigation of the Origin of the Old Norse or Icelandic Language'), where he argued that [[Old Norse]] was related to the Germanic languages, and had even suggested a relation to the Baltic, Slavic, Greek, Latin and Romance languages.<ref>{{Cite book |last=Momma |first=Haruko |url=https://books.google.com/books?id=WGYzp7olz6QC |title=From Philology to English Studies: Language and Culture in the Nineteenth Century |date=2013 |publisher=[[Cambridge University Press]] |isbn=978-0-521-51886-4 |pages=65–66 |language=en |author-link=Haruko Momma}}</ref> In 1816, [[Franz Bopp]] published ''On the System of Conjugation in Sanskrit'', in which he investigated the common origin of Sanskrit, Persian, Greek, Latin, and German. In 1833, he began publishing the ''Comparative Grammar of Sanskrit, [[Avestan|Zend]], Greek, Latin, Lithuanian, Old Slavic, Gothic, and German''.<ref>{{Cite encyclopedia |url= https://www.britannica.com/biography/Franz-Bopp |title=Franz Bopp, German philologist |encyclopedia=[[Encyclopædia Britannica]] |access-date=26 August 2016}}</ref>

In 1822, [[Jacob Grimm]] formulated what became known as [[Grimm's law]] as a general rule in his {{lang|de|Deutsche Grammatik}}. Grimm showed correlations between the Germanic and other Indo-European languages and demonstrated that sound change systematically transforms all words of a language.<ref>{{Cite encyclopedia |url=https://www.britannica.com/topic/Grimms-law |title=Grimm's law, linguistics |encyclopedia=[[Encyclopædia Britannica]] |access-date=26 August 2016}}</ref> From the 1870s, the Neogrammarians proposed that sound laws have no exceptions, as illustrated by [[Verner's law]], published in 1876, which resolved apparent exceptions to Grimm's law by exploring the role of accent (stress) in language change.<ref>{{Cite encyclopedia |url=https://www.britannica.com/science/Neogrammarian |title=Neogrammarian, German scholar |encyclopedia=[[Encyclopædia Britannica]] |access-date=26 August 2016}}</ref>

[[August Schleicher]]'s ''A Compendium of the Comparative Grammar of the Indo-European, Sanskrit, Greek and Latin Languages'' (1874–77) represented an early attempt to reconstruct the Proto-Indo-European language.<ref>{{Cite encyclopedia |url=https://www.britannica.com/biography/August-Schleicher |title=August Schleicher, German linguist |encyclopedia=[[Encyclopædia Britannica]] |access-date=26 August 2016 }}</ref>

By the early 1900s, [[Indo-Europeanist]]s had developed well-defined descriptions of PIE which scholars still accept today. Later, the discovery of the [[Anatolian languages|Anatolian]] and [[Tocharian languages]] added to the corpus of descendant languages. A subtle new principle won wide acceptance: the [[laryngeal theory]], which explained irregularities in the reconstruction of Proto-Indo-European phonology as the effects of hypothetical sounds which no longer exist in all languages documented prior to the excavation of [[cuneiform]] tablets in Anatolian. This theory was first proposed by [[Ferdinand de Saussure]] in 1879 on the basis of internal reconstruction only,<ref>{{Cite book |last=Saussure |first=Ferdinand de |url=http://archive.org/details/memoiresurlesyst00saus |title=Mémoire sur le système primitif des voyelles dans les langues indo-européennes |date=1879 |publisher=Leipsick : B. G. Teubner |others=University of California Libraries}}</ref> and progressively won general acceptance after [[Jerzy Kuryłowicz]]'s discovery of consonantal reflexes of these reconstructed sounds in Hittite.<ref>Kuryłowicz, Jerzy (1927). "''ə'' indo-européen et ''ḫ'' hittite". In: Witold Taszycki and Witold Doroszewki (eds.), ''Symbolae Grammaticae in honorem Ioannis Rozwadowski'', v. 1, 95–104. Krakow: Uniwersytet Jagielloński.</ref>

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

In ''The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World'', Mallory and Adams illustrate the resemblance with the following examples of [[cognate]] forms (with the addition of Old English for further comparison):{{sfn|Mallory|Adams|2006|pp=3, 5, 135, 209–210}}
:{| class="wikitable"  style="vertical-align:center;"
|+ Examples of cognate words in Indo-European languages
|- style="vertical-align:bottom;"
!  {{nobr|&emsp; PIE &emsp;}}
! [[English language|Modern<br/>&nbsp;English&nbsp;]]
! [[Old English language|Old<br/>&nbsp;English&nbsp;]]
! &nbsp;&nbsp;[[Latin language|Latin]]&nbsp;&nbsp;
! &nbsp;&nbsp;[[Greek language|Greek]]&nbsp;&nbsp;
! &nbsp;[[Sanskrit language|Sanskrit]]&nbsp;
|- style="vertical-align:center;"
| &nbsp;*méh₂tēr&nbsp;
| &nbsp;mother
| &nbsp;mōdor
| &nbsp;māter
| &nbsp;mḗtēr
| &nbsp;mātár-
|- style="vertical-align:center;"
| &nbsp;*ph₂tḗr&nbsp;
| &nbsp;father
| &nbsp;fæder
| &nbsp;pater
| &nbsp;patḗr
| &nbsp;pitár-
|- style="vertical-align:center;"
| &nbsp;*bʰréh₂tēr&nbsp;
| &nbsp;brother
| &nbsp;brōþor
| &nbsp;frāter
| &nbsp;phrḗtēr
| &nbsp;bhrā́tar-
|- style="vertical-align:center;"
| &nbsp;*swésōr&nbsp;
| &nbsp;sister
| &nbsp;sweostor
| &nbsp;soror
| &nbsp;éor
| &nbsp;svásar-
|- style="vertical-align:center;"
| &nbsp;*suHnús,&nbsp;<br/>&nbsp;*suHyús&nbsp;
| &nbsp;son
| &nbsp;sunu
| {{center| — }}
| &nbsp;huiús
| &nbsp;sūnú-
|- style="vertical-align:center;"
| &nbsp;*dʰugh₂tḗr&nbsp;
| &nbsp;daughter
| &nbsp;dohtor
| {{center| — }}
| &nbsp;thugátēr
| &nbsp;duhitár-
|- style="vertical-align:center;"
| &nbsp;*gʷṓus&nbsp;
| &nbsp;cow
| &nbsp;cū
| &nbsp;bōs
| &nbsp;boûs
| &nbsp;gáu-
|}

==Historical and geographical setting==
{{main|Proto-Indo-European homeland}}
[[File:Indo-European migrations.jpg|thumb|300px|Early [[Indo-European migrations]] from the [[Pontic steppes]] and across Central Asia according to the widely held Kurgan hypothesis]]
{{anchor|Era}}{{anchor|Region}}Scholars have proposed multiple hypotheses about when, where, and by whom PIE was spoken. The [[Kurgan hypothesis]], first put forward in 1956 by [[Marija Gimbutas]], has become the most popular.{{efn|See:
* Bomhard: "This scenario is supported not only by linguistic evidence, but also by a growing body of archeological and genetic evidence. The Indo-Europeans have been identified with several cultural complexes existing in that area between 4,500—3,500 BCE. The literature supporting such a homeland is both extensive and persuasive [...]. Consequently, other scenarios regarding the possible Indo-European homeland, such as Anatolia, have now been mostly abandoned."{{sfn|Bomhard|2019|p=2}}
*Anthony & Ringe: "Archaeological evidence and linguistic evidence converge in support of an origin of Indo-European languages on the Pontic-Caspian steppes around 4,000 years BCE. The evidence is so strong that arguments in support of other hypotheses should be reexamined."{{sfn|Anthony|Ringe|2015|pp=199–219}}
* Mallory: "The Kurgan solution is attractive and has been accepted by many archaeologists and linguists, in part or total. It is the solution one encounters in the ''Encyclopædia Britannica'' and the ''Grand Dictionnaire Encyclopédique Larousse''."{{sfn|Mallory|1989|p=185}}
* Strazny: "The single most popular proposal is the Pontic steppes (see the Kurgan hypothesis)..."{{sfn|Strazny|2000|p=163}}}} It proposes that the original speakers of PIE were the [[Yamnaya culture]] associated with the [[kurgan]]s (burial mounds) on the [[Pontic–Caspian steppe]] north of the Black Sea.<ref>{{cite book|title= The horse, the wheel, and language: how bronze-age riders from the Eurasian steppes shaped the modern world|date= 2007|publisher= Princeton University Press|isbn= 978-0-691-05887-0|edition= 8th reprint|location= Princeton, N.J.|last1= Anthony|first1= David W.|author-link1= David W. Anthony|title-link= The Horse, the Wheel, and Language}}</ref>{{rp|305–7}}<ref name="Science">{{cite journal|url= https://www.science.org/content/article/mysterious-indo-european-homeland-may-have-been-steppes-ukraine-and-russia|title= Mysterious Indo-European homeland may have been in the steppes of Ukraine and Russia|last= Balter|first= Michael|date= 13 February 2015|journal= Science|doi= 10.1126/science.aaa7858|access-date= 17 February 2015|url-access= subscription}}</ref> According to the theory, they were [[Eurasian nomads|nomadic pastoralists]] who [[domestication of the horse|domesticated the horse]], which allowed them to migrate across Europe and Asia in wagons and chariots.<ref name="Science" /> By the early 3rd millennium BCE, they had expanded throughout the Pontic–Caspian steppe and into eastern Europe.<ref>{{Cite journal|last= Gimbutas|first= Marija|year= 1985|title= Primary and Secondary Homeland of the Indo-Europeans: comments on Gamkrelidze-Ivanov articles|journal= Journal of Indo-European Studies|volume= 13|issue= 1–2|pages= 185–202}}</ref> In 2024, a pair of studies led by Harvard biologist [[David Reich (geneticist)|David Reich]] argued that the original speakers of PIE originated in the Caucusus-Lower Volga region during the [[Eneolithic Period]].<ref>{{Cite web |title=Harvard Researchers Discover Origin of Indo-European Language Family {{!}} News {{!}} The Harvard Crimson |url=https://www.thecrimson.com/article/2025/2/12/indo-european-language-research/ |access-date=2025-06-16 |website=www.thecrimson.com}}</ref>

Other theories include the [[Anatolian hypothesis]],<ref name="bouckaert">{{Citation|title= Mapping the Origins and Expansion of the Indo-European Language Family|date= 24 August 2012|last1= Bouckaert|last2= Lemey|last3= Dunn|last4= Greenhill|last5= Alekseyenko|last6= Drummond|last7= Gray|last8= Suchard|first1= Remco|first2= P.|first3= M.|first4= S. J.|first5= A. V.|first6= A. J.|first7= R. D.|first8= M. A.|journal= Science|volume= 337|issue= 6097|pages= 957–960|doi= 10.1126/science.1219669|pmc= 4112997|pmid=22923579|display-authors= etal|bibcode= 2012Sci...337..957B|url= http://pubman.mpdl.mpg.de/pubman/item/escidoc:1539154/component/escidoc:1539165/Bouckaert_2012.pdf|hdl= 11858/00-001M-0000-000F-EADF-A}}</ref> which posits that PIE spread out from Anatolia with agriculture beginning {{circa}} 7500–6000 BCE,<ref>{{Cite journal|last1=Chang|first1=Will|last2=Cathcart|first2=Chundra|last3=Hall|first3=David|last4=Garrett|first4=Andrew|date=2015|title=Ancestry-constrained phylogenetic analysis supports the Indo-European steppe hypothesis|url=https://muse.jhu.edu/content/crossref/journals/language/v091/91.1.chang.html|journal=Language|language=en|volume=91|issue=1|pages=194–244|doi=10.1353/lan.2015.0005| s2cid=143978664 |issn=1535-0665}}</ref> the [[Armenian hypothesis]], the [[Paleolithic continuity paradigm]], and the [[indigenous Aryans]] theory. The last two of these theories are not regarded as credible within academia.<ref>[[Romila Thapar|Thapar, Romila]] (2006). ''[https://books.google.com/books?id=sDBuAAAAMAAJ&q=%22there+is+no+scholar+at+this+time+seriously%22 India: Historical Beginnings and the Concept of the Aryan]''. National Book Trust. p. 127. {{ISBN|9788123747798}}.</ref><ref>"The opposing argument, that speakers of Indo-European languages were indigenous to the Indian subcontinent, is not supported by any reliable scholarship". [[Wendy Doniger|Doniger, Wendy]] (2017). [https://inference-review.com/article/another-great-story "Another Great Story"] {{Webarchive|url=https://web.archive.org/web/20230514094423/https://inference-review.com/article/another-great-story |date=14 May 2023 }}", review of Asko Parpola's ''The Roots of Hinduism''. In: ''Inference, International Review of Science'', Volume 3, Issue 2.</ref> Out of all the theories for a PIE homeland, the Kurgan and Anatolian hypotheses are the ones most widely accepted, and also the ones most debated against each other.<ref>{{Cite book |last=Mallory |first=J. P. |title=The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World |date=2006 |publisher=Oxford University Press |others=Douglas Q. Adams |isbn=978-1-4294-7104-6 |location=New York |oclc=139999117}}</ref> Following the publication of several studies on ancient DNA in 2015, Colin Renfrew, the original author and proponent of the Anatolian hypothesis, has accepted the reality of migrations of populations speaking one or several Indo-European languages from the Pontic steppe towards Northwestern Europe.<ref>Renfrew, Colin (2017) "[https://www.youtube.com/watch?v=pmv3J55bdZc Marija Redivia : DNA and Indo-European origins]" (''The Oriental Institute lecture series : Marija Gimbutas memorial lecture'', Chicago. November 8, 2017).</ref><ref name=":4">{{Cite journal|last1=Pellard|first1=Thomas|last2=Sagart|first2=Laurent|author-link2=Laurent Sagart|last3=Jacques|first3=Guillaume|date=2018|title=L'indo-européen n'est pas un mythe|journal=Bulletin de la Société de Linguistique de Paris|volume=113|issue=1|pages=79–102|doi=10.2143/BSL.113.1.3285465|s2cid=171874630 }}</ref>

[[File:IndoEuropeanTree.svg|thumb|center|upright=2.5|Classification of Indo-European languages.{{citation needed|date=December 2024|reason=Graphic doesn't identify sources supporting this organization (even at Commons).}} Red: Extinct languages. White: categories or unattested proto-languages. Left half: [[centum]] languages; right half: [[satem]] languages]]

==Descendants==
{{main|Indo-European languages}}
The antiquity of the earliest attestation (in units of 500 years) of each Indo-European group is: 2000–1500 BCE for Anatolian; 1500–1000 BCE for Indo-Aryan and Greek; 1000–500 BCE for Iranic, Celtic, Italic, Phrygian, Illyric, Messapic, South Picene, and Venetic; 500–1 BCE for Thracian and Ancient Macedonian; 1–500 CE for Germanic, Armenian, Lusitanian, and Tocharian; 500–1000 CE for Slavic; 1500–2000 CE for Albanian and Baltic.{{sfn|Mallory|Adams|2006|p=14}}

The table lists the main Indo-European language families, comprising the languages descended from Proto-Indo-European.
{| class="wikitable"
!Clade
!Proto-language
!Description
!Historical languages
!Modern descendants
|-
|[[Anatolian languages|Anatolian]]
|[[Proto-Anatolian language|Proto-Anatolian]]
|All now extinct, the best attested being the [[Hittite language]].
|[[Hittite language|Hittite]], [[Luwian language|Luwian]], [[Palaic]], [[Lycian language|Lycian]], [[Lydian language|Lydian]], [[Carian language|Carian]], [[Pisidian language|Pisidian]], [[Sidetic language|Sidetic]], [[Milyan language|Milyan]]
|There are no living descendants of Proto-Anatolian.
|-
|[[Tocharian languages|Tocharian]]
|[[Proto-Tocharian language|Proto-Tocharian]]
|An extinct branch known from manuscripts dating from the 6th to the 8th century AD and found in northwest China.
|[[Tocharian A]], [[Tocharian B]]
|There are no living descendants of Proto-Tocharian.
|-
|[[Italic languages|Italic]]
|[[Proto-Italic language|Proto-Italic]]
|This included many languages, but only descendants of [[Latin]] (the [[Romance languages]]) survive.
|[[Latin]], [[Faliscan language|Faliscan]], [[Umbrian]], [[Oscan]], [[African Romance]], [[Dalmatian language|Dalmatian]], [[Volscian language|Volscian]], [[Marsi]], [[Pre-Samnite language|Pre-Samnite]], [[Paeligni]], [[Sabines|Sabine]]
|[[Portuguese language|Portuguese]], [[Galician language|Galician]], [[Spanish language|Spanish]], [[Judaeo-Spanish|Ladino]], [[Catalan language|Catalan]], [[Occitan languages|Occitan]], [[French language|French]], [[Italian language|Italian]], [[Friulian language|Friulian]], [[Romansh language|Romansh]], [[Romanian language|Romanian]], [[Aromanian language|Aromanian]], [[Sardinian language|Sardinian]], [[Corsican language|Corsican]], [[Venetian language|Venetian]], Latin (as a [[liturgical language]] of the Catholic Church and the official language of the [[Vatican City]]), [[Picard language|Picard]], [[Mirandese language|Mirandese]], [[Aragonese language|Aragonese]], [[Walloon language|Walloon]], [[Piedmontese language|Piedmontese]], [[Lombard language|Lombard]], [[Neapolitan language|Neapolitan]], [[Sicilian language|Sicilian]], [[Emilian-Romagnol language|Emilian-Romagnol]], [[Ligurian language|Ligurian]], [[Ladin language|Ladin]] 
|-
|[[Celtic languages|Celtic]]
|[[Proto-Celtic language|Proto-Celtic]]
|Once spoken across Europe and Anatolia (Asia Minor), but now mostly confined to Europe's northwestern edge.
|[[Gaulish]], [[Lepontic language|Lepontic]], [[Noric language|Noric]], [[Pictish]], [[Cumbric]], [[Old Irish language|Old Irish]], [[Middle Welsh language|Middle Welsh]], [[Gallaecian language|Gallaecian]], [[Galatian language|Galatian]], [[Celtiberian language|Celtiberian]]
|[[Irish language|Irish]], [[Scottish Gaelic]], [[Welsh language|Welsh]], [[Breton language|Breton]], [[Cornish language|Cornish]], [[Manx language|Manx]]
|-
|[[Germanic languages|Germanic]]
|[[Proto-Germanic language|Proto-Germanic]]
|Branched into three subfamilies: [[West Germanic languages|West Germanic]], [[East Germanic languages|East Germanic]] (now extinct), and [[North Germanic languages|North Germanic]].
|[[Old English]], [[Old Norse]], [[Gothic language|Gothic]], [[Old High German]], [[Old Saxon]], [[Vandalic language|Vandalic]], [[Burgundian language (Germanic)|Burgundian]], [[Crimean Gothic]], [[Norn language|Norn]], [[Greenlandic Norse]]
|[[English language|English]], [[German language|German]], [[Afrikaans]], [[Dutch language|Dutch]], [[Yiddish]], [[Norwegian language|Norwegian]], [[Danish language|Danish]], [[Swedish language|Swedish]], [[Frisian languages|Frisian]], [[Icelandic language|Icelandic]], [[Faroese language|Faroese]], [[Luxembourgish language|Luxembourgish]], [[Scots language|Scots]], [[Limburgish]], [[Wymysorys language|Wymysorys]], [[Elfdalian]]
|-
|[[Balto-Slavic languages|Balto-Slavic]]
|[[Proto-Balto-Slavic language|Proto-Balto-Slavic]]
|Branched into the [[Baltic languages]] and the [[Slavic languages]].
|[[Old Prussian]], [[Old Church Slavonic]], [[Sudovian language|Sudovian]], [[Semigallian language|Semigallian]], [[Selonian language|Selonian]], [[Skalvian language|Skalvian]], [[Galindian language|Galindian]], [[Polabian language|Polabian]], [[Knaanic language|Knaanic]]
|Baltic: [[Latvian language|Latvian]], [[Latgalian language|Latgalian]] and [[Lithuanian language|Lithuanian]];
Slavic: [[Russian language|Russian]], [[Ukrainian language|Ukrainian]], [[Belarusian language|Belarusian]], [[Polish language|Polish]], [[Czech language|Czech]], [[Slovak language|Slovak]], [[Sorbian languages|Sorbian]], [[Serbo-Croatian]], [[Bulgarian language|Bulgarian]], [[Slovenian language|Slovenian]], [[Macedonian language|Macedonian]], [[Kashubian language|Kashubian]], [[Rusyn language|Rusyn]]
|-
|[[Indo-Iranian languages|Indo-Iranian]]
|[[Proto-Indo-Iranian language|Proto-Indo-Iranian]]
|Branched into the [[Indo-Aryan languages|Indo-Aryan]], [[Iranian languages|Iranian]] and [[Nuristani languages|Nuristani]] languages.
|[[Vedic Sanskrit]], [[Pali language|Pali]], [[Prakrit|Prakrit languages]]; [[Old Persian]], [[Parthian language|Parthian]], [[Old Azeri]], [[Median language|Median]], [[Elu]], [[Sogdian language|Sogdian]], [[Saka language|Saka]], [[Avestan language|Avestan]], [[Bactrian language|Bactrian]]
|Indo-Aryan: [[Hindustani language|Hindustani]] ([[Hindi]] and [[Urdu]]), [[Marathi language|Marathi]], [[Sylheti language|Sylheti]], [[Bengali language|Bengali]], [[Assamese language|Assamese]], [[Odia language|Odia]], [[Konkani language|Konkani]], [[Gujarati language|Gujarati]], [[Nepali language|Nepali]], [[Dogri language|Dogri]], [[Romani language|Romani]], [[Sindhi language|Sindhi]], [[Maithili language|Maithili]], [[Sinhala language|Sinhala]], [[Dhivehi language|Dhivehi]], [[Punjabi language|Punjabi]], [[Kashmiri language|Kashmiri]], [[Sanskrit]] ([[Revived language|revived]]);
Iranian: [[Persian language|Persian]], [[Pashto]], [[Balochi language|Balochi]], [[Kurdish languages|Kurdish]], [[Zaza language|Zaza]], [[Ossetian language|Ossetian]], [[Luri language|Luri]], [[Talysh language|Talyshi]], [[Tati language (Iran)|Tati]], [[Gilaki language|Gilaki]], [[Mazanderani language|Mazandarani]], [[Semnani language|Semnani]], [[Yaghnobi language|Yaghnobi]];

Nuristani: [[Katë language|Katë]], [[Prasun language|Prasun]], [[Ashkun language|Ashkun]], [[Nuristani Kalasha language|Nuristani Kalasha]], [[Tregami language|Tregami]], [[Zemiaki language|Zemiaki]]

|-
|[[Armenian language|Armenian]]
|[[Proto-Armenian language|Proto-Armenian]]
|Armenian is the only surviving representative of the Armenian branch of the Indo-European language family.
|[[Classical Armenian]]
|[[Armenian language|Armenian]] ([[Eastern Armenian|Eastern]] and [[Western Armenian|Western]])
|-
|[[Hellenic languages|Hellenic]]
|[[Proto-Greek language|Proto-Greek]]
|Modern Greek and Tsakonian are the only surviving varieties of Greek.
|[[Ancient Greek]], [[Ancient Macedonian language|Ancient Macedonian]] 
|[[Greek language|Greek]], [[Tsakonian language|Tsakonian]]
|-
|[[Albanian language|Albanian]]
|[[Proto-Albanian language|Proto-Albanian]]
|Albanian is the only surviving representative of the [[Albanoid]] branch of the Indo-European language family.<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. 383–386.</ref><ref>{{cite web|url= http://www.cs.rice.edu/~nakhleh/Papers/81.2nakhleh.pdf |title= Perfect Phylogenetic Networks: A New Methodology for Reconstructing the Evolutionary History of Natural Languages, pg. 396 |access-date= 22 September 2010 | archive-url= https://web.archive.org/web/20101105223804/http://www.cs.rice.edu/~nakhleh/Papers/81.2nakhleh.pdf | archive-date= 5 November 2010 | url-status = live}}</ref>
|[[Illyrian language|Illyrian]] (disputed); [[Daco-Thracian]] (disputed)
|[[Albanian language|Albanian]] ([[Gheg Albanian|Gheg]] and [[Tosk Albanian|Tosk]])
|}

Commonly proposed subgroups of Indo-European languages include [[Italo-Celtic]], [[Graeco-Aryan]], [[Graeco-Armenian]], [[Graeco-Phrygian]], [[Daco-Thracian]], and [[Thraco-Illyrian]].

There are numerous lexical similarities between the Proto-Indo-European and [[Proto-Kartvelian language|Proto-Kartvelian]] languages due to early [[language contact]],{{Citation needed|date=March 2023}} as well as some morphological similarities—notably the [[Indo-European ablaut]], which is remarkably similar to the root ablaut system reconstructible for Proto-Kartvelian.<ref>Gamkrelidze, Th. & Ivanov, V. (1995). Indo-European and the Indo-Europeans: A Reconstruction and Historical Analysis of a Proto-Language and a Proto-Culture. 2 Vols. Berlin and New York: Mouton de Gruyter.</ref><ref>Gamkrelidze, T. V. (2008). Kartvelian and Indo-European: a typological comparison of reconstructed linguistic systems. Bulletin of the Georgian National Academy of Sciences 2 (2): 154–160.</ref>

===Marginally attested languages===
The [[Lusitanian language]] was a marginally attested language spoken in areas near the border between present-day [[Portugal]] and [[Spain]].

The [[Venetic language|Venetic]] and [[Liburnian language|Liburnian]] languages known from the North Adriatic region are sometimes classified as Italic.

Albanian and Greek are the only surviving Indo-European descendants of a [[Paleo-Balkan languages|Paleo-Balkan]] language area, named for their occurrence in or in the vicinity of the [[Balkan peninsula]]. Most of the other languages of this area—including [[Illyrian languages|Illyrian]], [[Thracian language|Thracian]], and [[Dacian language|Dacian]]—do not appear to be members of any other subfamilies of PIE, but are so poorly attested that proper classification of them is not possible. Forming an exception, [[Phrygian language|Phrygian]] is sufficiently well-attested to allow proposals of a particularly close affiliation with Greek, and a [[Graeco-Phrygian]] branch of Indo-European is becoming increasingly accepted.<ref>{{cite book|last=Brixhe|first=Claude|year=2008|chapter=Phrygian|editor-last=Woodard|editor-first=Roger D.|title=The Ancient Languages of Asia Minor|publisher=Cambridge University Press|page=72|isbn=9781139469333|chapter-url=https://books.google.com/books?id=J-f_jwCgmeUC&pg=PA72}}</ref><ref>{{cite book |last1=Ligorio |first1=Orsat |last2=Lubotsky |first2=Alexander |chapter=101. Phrygian |year=2018 |editor1=Jared Klein |editor2=Brian Joseph |editor3=Matthias Fritz |title=Handbook of Comparative and Historical Indo-European Linguistics |location=Berlin, Boston |publisher=De Gruyter Mouton |pages=1816–1831 |series=HSK 41.3 |doi=10.1515/9783110542431-022 |hdl=1887/63481 |isbn=9783110542431 |s2cid=242082908 |chapter-url=https://www.academia.edu/36922557}}</ref><ref>{{Cite journal|last=Obrador-Cursach|first=Bartomeu|date=2019|title=On the place of Phrygian among the Indo-European languages|journal=Journal of Language Relationship|volume=17|issue=3–4|pages=239|doi=10.31826/jlr-2019-173-407|s2cid=215769896|doi-access=free}}</ref>

==Phonology==
{{Main|Proto-Indo-European phonology}}

Proto-Indo-European [[phonology]] has been reconstructed in some detail. Notable features of the most widely accepted (but not uncontroversial) reconstruction include:
*three series of [[stop consonant]]s reconstructed as [[voiceless consonant|voiceless]], [[voiced consonant|voiced]], and [[breathy voice]]d;
*[[sonorant]] consonants that could be used [[syllabic consonant|syllabically]];
*three so-called [[laryngeal theory|laryngeal]] consonants, whose exact pronunciation is not well-established but which are believed to have existed in part based on their detectable effects on adjacent sounds;
*the [[fricative]] {{IPA|/s/}}
*a [[vowel]] system in which {{IPA|/e/}} and {{IPA|/o/}} were the most frequently occurring vowels. The existence of {{IPA|/a/}} as a separate phoneme is debated.

===Notation===

====Vowels====
The vowels in commonly used notation are:{{sfnp|Kapović|2017|p=13}}

{| class="wikitable"
|+
!Type
![[Front vowel|front]]
![[Back vowel|back]]
|-
! [[Mid vowel|Mid]]
|{{IPA|*[[Mid front unrounded vowel|e]]}}, *ē /[[Mid front unrounded vowel|eː]]/
|{{IPA|*[[Mid back rounded vowel|o]]}}, *ō /[[Mid back rounded vowel|oː]]/
|-
! [[Low vowel|Low]]
|{{IPA|*[[Open front unrounded vowel|a]]}}?
|}

====Consonants====
The corresponding consonants in commonly used notation are:{{sfnp|Fortson|2010|loc=§3.2}}{{sfnp|Beekes|1995|loc=§11}}

{| class="wikitable" style="text-align: center"
|-
! rowspan="2" colspan="2" |
! rowspan="2" | [[labial consonant|Labial]]
! rowspan="2" | [[Dental consonant|Dental]] or [[alveolar consonant|Alveolar]]
! colspan="3" | [[velar consonant|Velar]]
! colspan="3" | [[Laryngeal consonant|Laryngeal]]
! rowspan="6" |
|-
! <small>[[Palatalization (phonetics)|palatalised]]</small>
! <small>[[Velar consonant|plain]]</small>
! <small>[[Labialized velar consonant|labialised]]</small>
! colspan="2" |<small>[[Velar consonant|velar]] or [[Uvular consonant|uvular]]</small>
!  |<small>[[glottal consonant|glottal]]</small>
|-
! colspan="2" | [[Nasal consonant|Nasals]]
| {{lang|ine-x-proto|m}} {{IPAslink|m}}
| {{lang|ine-x-proto|n}} {{IPAslink|n}}
| colspan=3| {{lang|ine-x-proto|n}} {{IPAblink|ŋ}}
|
|
|-
! rowspan=3| [[Stop consonant|Stops]]
! <small>[[Voicelessness|voiceless]]</small>
| {{lang|ine-x-proto|p}} {{IPAslink|p}}
| {{lang|ine-x-proto|t}} {{IPAslink|t}}
| *ḱ {{IPAslink|kʲ}}
| {{lang|ine-x-proto|k}} {{IPAslink|k}}
| {{lang|ine-x-proto|kʷ}} {{IPAslink|kʷ}}
|
|
|
|-
! <small>[[Voice (phonetics)|voiced]]</small>
| {{lang|ine-x-proto|b}} {{IPAslink|b}}
| {{lang|ine-x-proto|d}} {{IPAslink|d}}
| *ǵ {{IPAslink|ɡʲ}}
| {{lang|ine-x-proto|g}} {{IPAslink|ɡ}}
| {{lang|ine-x-proto|gʷ}} {{IPAslink|ɡʷ}}
|
|
|
|-
! <small>[[Breathy voice|aspirated]]</small>
| {{lang|ine-x-proto|bʰ}} {{IPAslink|bʱ}}
| {{lang|ine-x-proto|dʰ}} {{IPAslink|dʱ}}
| *ǵʰ {{IPAslink|ɡʲʱ}}
| {{lang|ine-x-proto|gʰ}} {{IPAslink|ɡʱ}}
| {{lang|ine-x-proto|gʷʰ}} {{IPAslink|ɡʷʱ}}
|
|
|
|-
! colspan="2" rowspan="2" | [[Fricative consonant|Fricatives]]
| rowspan="2" |
| rowspan="2" | {{lang|ine-x-proto|s}} {{IPAslink|s}}, {{IPAblink|z}}
| rowspan="2" | || rowspan="2" | || rowspan="2" |
|{{lang|ine-x-proto|h₃}} {{IPAslink|ɣʷ}}~{{IPAslink|qʷː}}
|{{lang|ine-x-proto|h₂}} {{IPAslink|x}}~{{IPAslink|qː}}
| {{lang|ine-x-proto|h₁}} {{IPAslink|h}}~{{IPAslink|ʔ}}
!<small>[[Laryngeal theory|Laryngeal]] Pronunciation<br />([[Jens Elmegård Rasmussen|J. E. Rasmussen]], [[Alwin Kloekhorst|Kloekhorst]])</small>
|-
|{{IPAblink|ɵ}}
|{{IPAblink|ɐ}}
|{{IPAblink|ə}}
!<small>[[Syllabic consonant|Syllabic]] [[allophone]]</small>
|-
! rowspan="2" | [[Liquid consonant|Liquids]]
![[Trill consonant|Trill]]
|
| {{lang|ine-x-proto|r}} {{IPAslink|r}}
|
|
|
|
|
|
! rowspan="3" |
|-
![[Lateral consonant|Lateral]]
|
|{{lang|ine-x-proto|l}} {{IPAslink|l}}
|
|
|
|
|
|-
! colspan="2" rowspan="2" | [[Semivowels]]
| rowspan="2" |
| rowspan="2" |
| {{lang|ine-x-proto|y}} {{IPAslink|j}}
| rowspan="2" |
| {{lang|ine-x-proto|w}} {{IPAslink|w}}
| rowspan="2" |
| rowspan="2" |
| rowspan="2" |
|-
|*i {{IPAblink|i}}
|*u {{IPAblink|u}}
!<small>Syllabic allophone{{sfnp|Kapović|2017|p=14}}</small>
|}

All [[sonorant]]s (i.e. nasals, liquids and semivowels) can appear in [[Syllabic consonant|syllabic]] position. The syllabic allophones of *y and *w are realized as the surface vowels *i and *u respectively.{{sfnp|Kapović|2017|p=14}}

{{IPAblink|z}} is an allophone of {{lang|ine-x-proto|s}} when next to a voiced consonant.

{{IPAblink|ŋ}} is an allophone of {{lang|ine-x-proto|n}} before velar consonants.

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

The accent is best preserved in [[Vedic Sanskrit]] and (in the case of nouns) [[Ancient Greek]], and indirectly attested in a number of phenomena in other IE languages, such as [[Verner's Law]] in the Germanic branch. Sources for Indo-European accentuation are also the [[Balto-Slavic languages|Balto-Slavic]] accentual system and ''plene'' spelling in [[Hittite language|Hittite]] cuneiform. To account for mismatches between the accent of Vedic Sanskrit and Ancient Greek, as well as a few other phenomena, a few historical linguists prefer to reconstruct PIE as a [[Tone (linguistics)|tone language]] where each [[morpheme]] had an inherent tone; the sequence of tones in a word then evolved, according to that hypothesis, into the placement of lexical stress in different ways in different IE branches.<ref>{{Cite journal |last=Kortlandt |first=Frederik |date=1986 |title=Proto-Indo-European tones |journal=Journal of Indo-European Studies |pages=153–160|s2cid=55314276 }}</ref>

==Morphology==
Proto-Indo-European, like its earliest attested descendants, was a highly inflected, [[fusional language]]. Suffixation and ablaut were the main methods of marking inflection, both for nominals and verbs. The subject of a sentence was in the nominative case and agreed in number and person with the verb, which was additionally marked for voice, tense, aspect, and mood.<ref name="ELL - PIE Morphology">{{Cite book |title=Encyclopedia of Language and Linguistics |publisher=[[Elsevier]] |year=2006 |isbn=9780080547848 |editor-last=Brown |editor-first=Keith |edition=2nd |language=en |chapter=Proto-Indo-European Morphology}}</ref>

===Root===
{{main|Proto-Indo-European root}}
Proto-Indo-European nominals and verbs were primarily composed of roots – [[affix]]-lacking [[morpheme]]s that carried the core [[Lexical (semiotics)|lexical]] meaning of a word. They were used to derive related words (cf. the English root "-''friend''-", from which are derived related words such as ''friendship,'' ''friendly'', ''befriend'', and newly coined words such as ''unfriend''). As a rule, roots were monosyllabic, and had the structure (s)(C)CVC(C), where the symbols C stand for consonants, V stands for a variable vowel, and optional components are in parentheses. All roots ended in a consonant and, although less certain, they appear to have started with a consonant as well.<ref name="ELL - PIE Morphology" />

A root plus a [[suffix]] formed a [[word stem]], and a word stem plus an [[Suffix#Inflectional_suffixes|inflectional ending]] formed a word. Proto-Indo-European was a [[fusional language]], in which [[inflection]]al morphemes signaled the grammatical relationships between words. This dependence on inflectional morphemes means that roots in PIE, unlike those in English, were rarely used without affixes.{{sfnp|Fortson|2010|loc=§4.2, §4.20}}

===Ablaut===
{{main|Indo-European ablaut}}
Many morphemes in Proto-Indo-European had short ''e'' as their inherent vowel; the [[Indo-European ablaut]] is the change of this short ''e'' to short ''o'', long ''e'' (''ē''), long ''o'' (''ō''), or no vowel. The forms are referred to as the "ablaut grades" of the morpheme—the ''e''-grade, ''o''-grade, zero-grade (no vowel), etc. This variation in vowels occurred both within [[inflectional morphology]] (e.g., different grammatical forms of a noun or verb may have different vowels) and [[derivational morphology]] (e.g., a verb and an associated abstract [[verbal noun]] may have different vowels).{{sfnp|Fortson|2010|pp=73–74}}

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

===Noun===
[[Proto-Indo-European nominals|Proto-Indo-European nouns]] were probably declined for eight or nine cases:{{sfnp|Fortson|2010|p=102}}
*[[Nominative case|nominative]]: marks the [[Subject (grammar)|subject]] of a verb. Words that follow a linking verb ([[copulative verb]]) and restate the subject of that verb also use the nominative case. The nominative is the dictionary form of the noun.
*[[Accusative case|accusative]]: used for the [[direct object]] of a [[transitive verb]].
*[[genitive case|genitive]]: marks a [[noun]] as modifying another noun.
*[[Dative case|dative]]: used to indicate the indirect object of a transitive verb, such as ''Jacob'' in ''Maria gave Jacob a drink''.
*[[Instrumental case|instrumental]]: marks the ''instrument'' or means by, or with, which the subject achieves or accomplishes an action. It may be either a physical object or an abstract concept.
*[[ablative case|ablative]]: used to express motion away from something.
*[[locative case|locative]]: expresses location, corresponding vaguely to the English prepositions ''in'', ''on'', ''at'', and ''by''.
*[[Vocative case|vocative]]: used for a word that identifies an addressee. A vocative is a [[noun of address]] where the identity of the party spoken to is set forth expressly within a sentence. For example, in the sentence, "I don't know, John", ''John'' is a noun of address, indicating the party being addressed.
*[[allative case|allative]]: used as a type of [[locative case]] that expresses movement towards something. It was preserved in Anatolian (particularly Old Hittite), and fossilized traces of it have been found in Greek. It is also present in Tocharian.<ref>{{Citation |last=Pinault |first=Georges-Jean |title=Handbook of Comparative and Historical Indo-European Linguistics |chapter=76. The morphology of Tocharian |date=2017-10-23 |chapter-url=https://www.degruyter.com/document/doi/10.1515/9783110523874-031/html |pages=1335–1352 |access-date=2023-03-08 |publisher=De Gruyter Mouton |language=en |doi=10.1515/9783110523874-031 |isbn=978-3-11-052387-4}}</ref> Its PIE shape is uncertain, with candidates including {{lang|ine-x-proto|*-h₂(e)}}, {{lang|ine-x-proto|*-(e)h₂}}, or {{lang|ine-x-proto|*-a}}.{{sfnp|Fortson|2010|pp=102, 105}}
Late Proto-Indo-European had three [[grammatical gender]]s:
* masculine
* feminine
* neuter
This system is probably derived from an older two-gender system, attested in Anatolian languages: [[Common gender|common]] (or [[Animate gender|animate]]) and neuter (or inanimate) gender. The feminine gender only arose in the later period of the language.<ref>{{Cite book|title=The Sanskrit Language|last=Burrow|first=T|year=1955|publisher=Motilal Banarsidass Publ. |isbn=81-208-1767-2}}</ref> Neuter nouns collapsed the nominative, vocative and accusative into a single form, the plural of which used a special [[Collective noun|collective]] suffix {{wt|ine-pro|-h₂|*-h₂}} (manifested in most descendants as {{lang|ine|-a}}). This same collective suffix in extended forms {{wt|ine-pro|-éh₂|*-eh₂}} and {{wt|ine-pro|-ih₂|*-ih₂}} (respectively on thematic and athematic nouns, becoming  {{lang|ine|-ā}} and  {{lang|ine|-ī}} in the early daughter languages) became used to form feminine nouns from masculines.

All nominals distinguished three [[Grammatical number|numbers]]:
* singular
* dual
* plural
These numbers were also distinguished in verbs (see [[#Verb|below]]), requiring [[Agreement (linguistics)|agreement]] with their subject nominal.

===Pronoun===
[[Proto-Indo-European pronouns]] are difficult to reconstruct, owing to their variety in later languages. PIE had personal [[pronoun]]s in the first and second [[grammatical person]], but not the third person, where [[demonstrative pronoun]]s were used instead. The personal pronouns had their own unique forms and endings, and some had [[Suppletion|two distinct stems]]; this is most obvious in the first person singular where the two stems are still preserved in English ''I'' and ''me''. There were also two varieties for the accusative, genitive and dative cases, a stressed and an [[enclitic]] form.<ref name="beekes">{{cite book|last=Beekes|first=Robert|title=Comparative Indo-European linguistics: an introduction|date=1995|publisher=J. Benjamins Publishing Company|location=Amsterdam|isbn=978-1556195044|pages=147, 212–217, 233, 243}}</ref>

{| class="wikitable" style="text-align: center;"
|+ Personal pronouns<ref name=beekes/>
! rowspan="2" | Case
! colspan="2" | First person
! colspan="2" | Second person
|-
! Singular
! Plural
! Singular
! Plural
|-
! [[Nominative case|Nominative]]
| {{lang|ine-x-proto|h₁eǵ(oH/Hom)}}
| {{lang|ine-x-proto|wei}}
| {{lang|ine-x-proto|tuH}}
| {{lang|ine-x-proto|yuH}}
|-
! [[Accusative case|Accusative]]
| {{lang|ine-x-proto|h₁mé}}, {{lang|ine-x-proto|h₁me}}
| {{lang|ine-x-proto|n̥smé}}, {{lang|ine-x-proto|nōs}}
| {{lang|ine-x-proto|twé}}
| {{lang|ine-x-proto|usmé}}, {{lang|ine-x-proto|wōs}}
|-
! [[Genitive case|Genitive]]
| {{lang|ine-x-proto|h₁méne}}, {{lang|ine-x-proto|h₁moi}}
| {{lang|ine-x-proto|n̥s(er)o-}}, {{lang|ine-x-proto|nos}}
| {{lang|ine-x-proto|tewe}}, {{lang|ine-x-proto|toi}}
| {{lang|ine-x-proto|yus(er)o-}}, {{lang|ine-x-proto|wos}}
|-
! [[Dative case|Dative]]
| {{lang|ine-x-proto|h₁méǵʰio}}, {{lang|ine-x-proto|h₁moi}}
| {{lang|ine-x-proto|n̥smei}}, {{lang|ine-x-proto|n̥s}}
| {{lang|ine-x-proto|tébʰio}}, {{lang|ine-x-proto|toi}}
| {{lang|ine-x-proto|usmei}}
|-
! [[Instrumental case|Instrumental]]
| {{lang|ine-x-proto|h₁moí}}
| {{lang|ine-x-proto|n̥smoí}}
| {{lang|ine-x-proto|toí}}
| {{lang|ine-x-proto|usmoí}}
|-
! [[Ablative case|Ablative]]
| {{lang|ine-x-proto|h₁med}}
| {{lang|ine-x-proto|n̥smed}}
| {{lang|ine-x-proto|tued}}
| {{lang|ine-x-proto|usmed}}
|-
! [[Locative case|Locative]]
| {{lang|ine-x-proto|h₁moí}}
| {{lang|ine-x-proto|n̥smi}}
| {{lang|ine-x-proto|toí}}
| {{lang|ine-x-proto|usmi}}
|}

===Verb===<!-- This section is linked from [[Vedic Sanskrit grammar]] -->
[[Proto-Indo-European verbs]], like the nouns, exhibited an ablaut system.

The most basic categorisation for the reconstructed Indo-European verb is [[grammatical aspect]]. Verbs are classed as:
*[[stative verb|stative]]: verbs that depict a state of being
*[[imperfective aspect|imperfective]]: verbs depicting ongoing, habitual or repeated action
*[[perfective aspect|perfective]]: verbs depicting a completed action or actions viewed as an entire process.
Verbs have at least four [[grammatical mood]]s:
*[[indicative mood|indicative]]: indicates that something is a statement of fact; in other words, to express what the speaker considers to be a known state of affairs, as in [[declarative sentence]]s.
*[[imperative mood|imperative]]: forms commands or requests, including the giving of prohibition or permission, or any other kind of advice or exhortation.
*[[subjunctive mood|subjunctive]]: used to express various states of unreality such as wish, emotion, possibility, judgment, opinion, obligation, or action that has not yet occurred
*[[optative mood|optative]]: indicates a wish or hope. It is similar to the [[cohortative mood]] and is closely related to the [[subjunctive mood]].
Verbs had two [[grammatical voice]]s:
* [[active voice|active]]: used in a clause whose subject expresses the main verb's [[Agent (grammar)|agent]].
*[[mediopassive voice|mediopassive]]: for the [[middle voice]] and the [[passive voice]].
Verbs had three [[grammatical person]]s: first, second and third.

Verbs had three [[grammatical number]]s:
*singular
*[[dual grammatical number|dual]]: referring to precisely two of the entities (objects or persons) identified by the noun or pronoun.
*[[plural]]: a number other than singular or dual.

Verbs were probably marked by a highly developed system of [[participle]]s, one for each combination of tense and voice, and an assorted array of [[verbal noun]]s and adjectival formations.

The following table shows a possible reconstruction of the PIE verb endings from Sihler, which largely represents the current consensus among Indo-Europeanists.
{| class="wikitable" style="text-align: center;"
! colspan="2" rowspan="2" | Person
! colspan="2"|'''Sihler (1995)'''<ref name="sihler">{{cite book|author-link1=Andrew Sihler|last1=Sihler|first1=Andrew L.|title=New comparative grammar of Greek and Latin|date=1995|publisher=Oxford Univ. Press|location=New York u.&nbsp;a.|isbn=0-19-508345-8}}</ref>
|-
! [[Athematic stem|Athematic]]
! [[Thematic stem|Thematic]]
|-
! rowspan=3 | [[Grammatical number|Singular]]
! [[Grammatical person|1st]]
| {{lang|ine-x-proto|-mi}}
| {{lang|ine-x-proto|-oh₂}}
|-
! 2nd
| {{lang|ine-x-proto|-si}}
| {{lang|ine-x-proto|-esi}}
|-
! 3rd
| {{lang|ine-x-proto|-ti}}
| {{lang|ine-x-proto|-eti}}
|-
! rowspan=3 | Dual
! 1st
| {{lang|ine-x-proto|-wos}}
| {{lang|ine-x-proto|-owos}}
|-
! 2nd
| {{lang|ine-x-proto|-th₁es}}
| {{lang|ine-x-proto|-eth₁es}}
|-
! 3rd
| {{lang|ine-x-proto|-tes}}
| {{lang|ine-x-proto|-etes}}
|-
! rowspan=3 | Plural
! 1st
| {{lang|ine-x-proto|-mos}}
| {{lang|ine-x-proto|-omos}}
|-
! 2nd
| {{lang|ine-x-proto|-te}}
| {{lang|ine-x-proto|-ete}}
|-
! 3rd
| {{lang|ine-x-proto|-nti}}
| {{lang|ine-x-proto|-onti}}
|}

===Numbers===
[[Proto-Indo-European numerals]] are generally reconstructed as follows:
{| class="wikitable" style="text-align: center;"
!Number
!'''Sihler'''<ref name="sihler"/>
|-
|one
|{{lang|ine-x-proto|(H)óynos}}/{{lang|ine-x-proto|(H)óywos}}/{{lang|ine-x-proto|(H)óyk(ʷ)os}}; {{lang|ine-x-proto|sḗm}} (full grade), {{lang|ine-x-proto|sm̥-}} ''(zero grade)''
|-
|two
|{{lang|ine-x-proto|d(u)wóh₁}} (full grade), {{lang|ine-x-proto|dwi-}} ''(zero grade)''
|-
|three
|{{lang|ine-x-proto|tréyes}} (full grade), {{lang|ine-x-proto|tri-}} ''(zero grade)''
|-
|four
|{{lang|ine-x-proto|kʷetwóres}} (''o''-grade), {{lang|ine-x-proto|kʷ(e)twr̥-}} ''(zero grade)''<br />(''see also the [[*kʷetwóres rule|{{lang|ine-x-proto|*kʷetwóres}} rule]]'')
|-
|five
|{{lang|ine-x-proto|pénkʷe}}
|-
|six
|{{lang|ine-x-proto|s(w)éḱs}}; ''originally perhaps'' {{lang|ine-x-proto|wéḱs}}, with {{lang|ine-x-proto|*s-}} under the influence of {{lang|ine-x-proto|septḿ̥}}
|-
|seven
|{{lang|ine-x-proto|septḿ̥}}
|-
|eight
|{{lang|ine-x-proto|oḱtṓ(w)}} ''or'' {{lang|ine-x-proto|h₃eḱtṓ(w)}}
|-
|nine
|{{lang|ine-x-proto|h₁néwn̥}}
|-
|ten
|{{lang|ine-x-proto|déḱm̥(t)}}
|}
Rather than specifically 100, {{lang|ine-x-proto|ḱm̥tóm}} may originally have meant "a large number".<ref>{{Citation|last=Lehmann|first=Winfried P|title=Theoretical Bases of Indo-European Linguistics|year=1993|pages=[https://archive.org/details/theoreticalbases0000lehm/page/252 252–55]|location=London|publisher=Routledge|isbn=0-415-08201-3|url=https://archive.org/details/theoreticalbases0000lehm/page/252}}</ref>

===Particle===
[[Proto-Indo-European particles]] were probably used both as [[adverb]]s and as [[Preposition and postposition|postpositions]]. These postpositions became prepositions in most daughter languages.

Reconstructed particles include for example, {{lang|ine-x-proto|upo}} "under, below"; the [[Affirmative and negative|negators]] {{lang|ine-x-proto|ne}}, {{lang|ine-x-proto|mē}}; the [[Conjunction (grammar)|conjunctions]] {{lang|ine-x-proto|kʷe}} "and", {{lang|ine-x-proto|wē}} "or" and others; and an [[interjection]], {{lang|ine-x-proto|wai!}}, expressing woe or agony.

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

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

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

In thematic stems, creating a possessive adjective seems to have involved shifting the accent one syllable to the right, for example:<ref name="Jay Jasanoff 21">{{cite book|author=Jay Jasanoff|title=The Prehistory of the Balto-Slavic Accent|page=21|author-link=Jay Jasanoff}}</ref>
* {{lang|ine-x-proto|*tómh₁-o-s}} "slice" ([[Ancient Greek]] {{lang|grc|τόμος}} {{lang|grc-Latn|tómos}}) > {{lang|ine-x-proto|*tomh₁-ó-s}} "cutting" (i.e. "making slices"; Greek {{lang|grc|τομός}} {{lang|grc-Latn|tomós}}) > {{lang|ine-x-proto|*dr-u-tomh₁-ó-s}} "cutting trees" (Greek {{lang|grc|δρυτόμος}} {{lang|grc-Latn|drutómos}} "woodcutter" with irregular accent).
* {{lang|ine-x-proto|*wólh₁-o-s}} "wish" ([[Vedic Sanskrit]] {{lang|vsn|वर}} {{transliteration|vsn|vára}}) > {{lang|ine-x-proto|*wolh₁-ó-s}} "having wishes" (Sanskrit {{lang|vsn|व॒र}} {{transliteration|vsn|vará}} "suitor").

In athematic stems, there was a change in the accent/ablaut class. The reconstructed four classes followed an ordering in which a derivation would shift the class one to the right:<ref name="Jay Jasanoff 21"/>
: acrostatic → proterokinetic → hysterokinetic → amphikinetic
The reason for this particular ordering of the classes in derivation is not known. Some examples:
* Acrostatic {{lang|ine-x-proto|*krót-u-s}} ~ {{lang|ine-x-proto|*krét-u-s}} "strength" (Sanskrit {{lang|vsn|क्रतु}} {{transliteration|vsn|krátu}} > proterokinetic {{lang|ine-x-proto|*krét-u-s}} ~ {{lang|ine-x-proto|*kr̥t-éw-s}} "having strength, strong" (Greek {{lang|grc|κρατύς}} {{transliteration|grc|kratús}}).
* Hysterokinetic {{lang|ine-x-proto|*ph₂-tḗr}} ~ {{lang|ine-x-proto|*ph₂-tr-és}} "father" (Greek {{lang|grc|πατήρ}} {{transliteration|grc|patḗr}}) > amphikinetic {{lang|ine-x-proto|*h₁su-péh₂-tōr}} ~ {{lang|ine-x-proto|*h₁su-ph₂-tr-és}} "having a good father" (Greek {{lang|grc|εὐπάτωρ}} {{transliteration|grc|eupátōr}}).

=====Vṛddhi=====
A [[vṛddhi]] derivation, named after the Sanskrit grammatical term, signifying "of, belonging to, descended from". It was characterised by "upgrading" the root grade, from zero to full (''e'') or from full to lengthened (''ē''). When upgrading from zero to full grade, the vowel could sometimes be inserted in an unexpected location, creating a different stem from the original full grade.

Examples:{{sfnp|Fortson|2010|pp=116f}}
* full grade {{lang|ine-x-proto|*sw'''é'''ḱuro-s}} "father-in-law" ([[Vedic Sanskrit]] {{lang|vsn|श्वशुर}} {{transliteration|vsn|śv'''á'''śura-}}) > lengthened grade {{lang|ine-x-proto|*sw'''ē'''ḱuró-s}} "relating to one's father-in-law" (Sanskrit {{lang|vsn|श्वाशुर}} {{lang|vsn-Latn|śv'''ā'''śura}}, [[Old High German]] {{lang|goh|swāgur}} "brother-in-law").
* full grade {{lang|ine-x-proto|*dyḗw-s}} > zero grade {{lang|ine-x-proto|*diw-és}} "sky" (Sanskrit {{lang|vsn|द्यौस्}} {{transliteration|vsn|dy'''á'''us}}) > new full grade {{lang|ine-x-proto|*d'''e'''yw-o-s}} "god, [[dyeus|sky god]]" (Sanskrit {{lang|vsn|दे॒वस्}} {{transliteration|vsn|d'''e'''vás}}, [[Ancient Greek]] {{lang|grc|Ζεύς}} {{transliteration|grc|Z'''e'''ús}}, [[Latin]] {{lang|la|d'''e'''us}}, etc.). Note the difference in vowel placement, {{lang|ine-x-proto|*dyew-}} in the full-grade stem of the original noun, but {{not a typo|{{lang|ine-x-proto|*deyw-}}}} in the vṛddhi derivative.

=====Nominalization=====
Adjectives with accent on the thematic vowel could be turned into nouns by moving the accent back onto the root. A zero grade root could remain so, or be "upgraded" to full grade like in a vṛddhi derivative. Some examples:<ref>{{cite book|author=Jay Jasanoff|title=The Prehistory of the Balto-Slavic Accent|page=22|author-link=Jay Jasanoff}}</ref>
* PIE {{lang|ine-x-proto|*ǵn̥h₁-tó-s}} ("born"; [[Vedic Sanskrit]] {{lang|vsn|जा॒त}} {{transliteration|vsn|jātá}}) > {{lang|ine-x-proto|*ǵénh₁-to-}} ("child", literally "thing that is born"; Sanskrit {{lang|vsn|जात}} {{transliteration|vsn|jāta}}; German {{lang|de|Kind}}).
* [[Ancient Greek]] {{lang|grc|λευκός}} {{transliteration|grc|leukós}} ("white") > {{lang|grc|λεῦκος}} {{transliteration|grc|leûkos}} (''a kind of fish'', literally "white one").
* Sanskrit {{lang|vsn|कृ॒ष्ण}} {{transliteration|vsn|kṛṣṇá}} ("dark") > {{lang|vsn|कृष्णस्}} {{transliteration|vsn|kṛ́ṣṇas}} ("antelope", literally "dark one").

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

====Affixal derivation====
{{empty section|date=May 2019}}

==Syntax==
The [[syntax]] of the older Indo-European languages has been studied in earnest since at least the late nineteenth century, by such scholars as [[Hermann Hirt]] and [[Berthold Delbrück]]. In the second half of the twentieth century, interest in the topic increased and led to reconstructions of Proto-Indo-European syntax.<ref>{{cite encyclopedia |title=Preface |encyclopedia=Proto-Indo-European Syntax and its Development |editor1-first=Leonid |editor1-last=Kulikov |editor2-first=Nikolaos |editor2-last=Lavidas |publisher=John Benjamins |year=2015}}</ref>

Since all the early attested IE languages were inflectional, PIE is thought to have relied primarily on morphological markers, rather than [[word order]], to signal [[syntax|syntactic]] relationships within sentences.{{r|eiec}} Still, a default ([[Markedness|unmarked]]) word order is thought to have existed in PIE. In 1892, [[Jacob Wackernagel]] reconstructed PIE's word order as [[subject–verb–object]] (SVO), based on evidence in Vedic Sanskrit.<ref name="hock">{{cite encyclopedia |title=Proto-Indo-European verb-finality: Reconstruction, typology, validation |first=Hans Henrich |last=Hock |author-link=Hans Henrich Hock |encyclopedia=Proto-Indo-European Syntax and its Development |editor1-first=Leonid |editor1-last=Kulikov |editor2-first=Nikolaos |editor2-last=Lavidas |publisher=John Benjamins |year=2015}}</ref>

[[Winfred P. Lehmann]] (1974), on the other hand, reconstructs PIE as a [[subject–object–verb]] (SOV) language. He posits that the presence of [[grammatical person|person marking]] in PIE verbs motivated a shift from OV to VO order in later dialects. Many of the descendant languages have VO order: modern Greek, [[Romance languages|Romance]] and [[Albanian language|Albanian]] prefer SVO, [[Insular Celtic]] has VSO as the default order, and even the [[Anatolian languages]] show some signs of this word order shift. [[Tocharian languages|Tocharian]] and [[Indo-Iranian languages|Indo-Iranian]], meanwhile, retained the conservative OV order. Lehmann attributes the context-dependent order preferences in Baltic, Slavic and Germanic to outside influences.<ref name="lehmann">{{Cite book|url=https://liberalarts.utexas.edu/lrc/resources/books/pies/7-developments.php|title=Proto-Indo-European Syntax|last=Lehmann|first=Winfred P.|publisher=University of Texas Press|year=1974|chapter=Syntactic Developments from PIE to the Dialects|isbn=9780292733411|author-link=Winfred P. Lehmann}}</ref> [[Donald Ringe]] (2006), however, attributes these to internal developments instead.<ref name="ringe">{{Cite book|last=Ringe|first=Donald|year=2006|title=Proto-Indo-European to Proto-Germanic|publisher=Oxford University Press}}</ref>

[[Paul Friedrich (linguist)|Paul Friedrich]] (1975) disagrees with Lehmann's analysis. He reconstructs PIE with the following syntax:
* basic SVO word order
* adjectives before nouns
* head nouns before [[genitive|genitives]]
* [[prepositions]] rather than postpositions
* no dominant order in [[comparison (grammar)|comparative constructions]]
* main clauses before [[relative clauses]]
Friedrich notes that even among those Indo-European languages with basic OV word order, none of them are ''rigidly'' OV. He also notes that these non-rigid OV languages mainly occur in parts of the IE area that overlap with OV languages from other families (such as [[Uralic]] and [[Dravidian languages|Dravidian]]), whereas VO is predominant in the central parts of the IE area. For these reasons, among others, he argues for a VO common ancestor.<ref name="friedrich">{{cite journal|last1=Friedrich|first1=Paul|author-link=Paul Friedrich (linguist)|title=Proto-Indo-European Syntax|journal=Journal of Indo-European Studies|publisher=University of Chicago Press|year=1975|volume=1|issue=1|isbn=0-941694-25-9}}</ref>

[[Hans Henrich Hock]] (2015) reports that the SVO hypothesis still has some adherents, but the "broad consensus" among PIE scholars is that PIE would have been an SOV language.{{r|hock}} The SOV default word order with other orders used to express emphasis (e.g., [[verb–subject–object]] to emphasise the verb) is attested in [[Old Indo-Aryan]], [[Old Iranian]], [[Old Latin]] and [[Hittite language|Hittite]], while traces of it can be found in the [[enclitic]] personal pronouns of the [[Tocharian languages]].<ref name="eiec">{{Cite encyclopedia |editor-first1=J. P. |editor-last1=Mallory |editor-first2=Douglas Q. |editor-last2=Adams |encyclopedia=[[Encyclopedia of Indo-European Culture]] |title=Proto-Indo-European |publisher=Taylor & Francis |year=1997 |page=463}}</ref>

==See also==
* [[Indo-European vocabulary]]
* [[Proto-Indo-European verbs]]
* [[Proto-Indo-European pronouns]]
* [[List of Indo-European languages]]
* [[Indo-European sound laws]]
* [[List of proto-languages]]

== Notes ==
{{notelist}}

==References==
{{Reflist}}

==Bibliography==
{{Refbegin|30em}}
* {{Cite journal |last1=Anthony |first1=David W. |last2=Ringe |first2=Don |year=2015 |title=The Indo-European Homeland from Linguistic and Archaeological Perspectives |journal=Annual Review of Linguistics |volume=1 |issue=1 |pages=199–219 |doi=10.1146/annurev-linguist-030514-124812|doi-access=free }}
* {{Cite journal |last=Bomhard |first=Allan |year=2019 |title=The Origins of Proto-Indo-European: The Caucasian Substrate Hypothesis |url=https://www.academia.edu/40002289 |journal=Journal of Indo-European Studies |volume=47 |issue=1–2}}
* {{Cite book |last=Clackson |first=James |url=https://www.cambridge.org/core/product/identifier/9780511808616/type/book |title=Indo-European Linguistics: An Introduction |date=2007-10-18 |publisher=Cambridge University Press |isbn=978-0-521-65367-1 |doi=10.1017/cbo9780511808616}}
* {{Cite book |last=Fortson |first=Benjamin W. |title=Indo-European language and culture: an introduction |publisher=Blackwell |year=2010 |isbn=978-1-405-18896-8 |edition=2nd |location=Malden, MA}}
* {{Cite book |last=Kapović |first=Mate |year=2017 |chapter=Proto-Indo-European phonology |editor-last=Kapović |editor-first=Mate |title=The Indo-European Languages |edition=2nd |location=London |publisher=Routledge |isbn=978-0-415-73062-4 |pages=13–60}}
* {{Cite book |last=Mallory |first=J. P. |url=https://archive.org/details/insearchofindoeu00jpma |title=In Search of the Indo-Europeans: Language, Archaeology, and Myth |year=1989 |publisher=Thames & Hudson |isbn=978-0-500-05052-1 |url-access=registration}}
* {{Citation |last1=Mallory |first1=J. P. |title=The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World |year=2006 |publisher=[[Oxford University Press]] |isbn=978-0-199-29668-2 |last2=Adams |first2=D. Q. |author-link=J. P. Mallory |author-link2=Douglas Q. Adams}}
* {{Citation |last=Meier-Brügger |first=Michael |title=Indo-European Linguistics |year=2003 |place=New York |publisher=De Gruyter |isbn=3-110-17433-2 |author-link=Meier-Brügger}}
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* {{Cite web |last=Kümmel |first=Martin Joachim |title=Uvular Stops or a Glottal Fricative? Theory and Data in Recent Reconstructions of PIE "Laryngeals" |url=https://archive.org/download/kummelljubljana2019.pdf_202011/k%C3%BCmmelljubljana2019.pdf.pdf |website=Seminar für Indogermanistik}}
* {{Citation |title=Handbook of Comparative and Historical Indo-European Linguistics |date=2017-09-25 |publisher=De Gruyter Mouton |volume=1 |doi=10.1515/9783110261288 |isbn=978-3-110-26128-8 |editor-last1=Klein |editor-last2=Joseph |editor-last3=Fritz |editor-first1=Jared |editor-first2=Brian |editor-first3=Matthias}}
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{{Refend}}

==External links==
{{Wiktionary|Appendix:Proto-Indo-European Swadesh list}}
* At the University of Texas Linguistic Research Center: [http://liberalarts.utexas.edu/lrc/resources/books/index.php List of online books] {{Webarchive|url=https://web.archive.org/web/20170728215921/http://liberalarts.utexas.edu/lrc/resources/books/index.php |date=28 July 2017 }}, [https://lrc.la.utexas.edu/lex Indo-European Lexicon]
* [http://pielexicon.hum.helsinki.fi/ Proto-Indo-European Lexicon] at the University of Helsinki, Department of Modern Languages, Department of World Cultures, Indo-European Studies
* {{cite web|url=https://archive.org/details/kummeleaa2019.pdf|title=Wheel and chariot in early IE: What exactly can we conclude from the linguistic data?|work=Martin Joachim Kümmel, department of Indo-European linguistics, [[University of Jena]]}}
* [http://ielex.mpi.nl/ Indo-European Lexical Cognacy Database] {{Webarchive|url=https://web.archive.org/web/20151107054612/http://ielex.mpi.nl/ |date=7 November 2015 }}
* [https://spw.uni-goettingen.de/projects/aig/index.html glottothèque – Ancient Indo-European Grammars online], an online collection of video lectures on Ancient Indo-European languages
{{Proto-Indo-European language}}

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{{DEFAULTSORT:Proto-Indo-European Language}}
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[[Category:Bronze Age]]
[[Category:Indo-European languages]]
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[[Category:Proto-languages|Indo-European]]