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The Proto-Indo-European language (PIE) is the reconstructed common ancestor of the Indo-European languages, spoken by the Proto-Indo-Europeans. PIE was the first proposed proto-language to be widely accepted by linguists. Far more work has gone into reconstructing it than any other proto-language, and it is by far the most well-understood of all proto-languages at its time depth. During the 19th century, the vast majority of linguistic work was devoted to reconstruction of Proto-Indo-European or of daughter proto-languages such as Proto-Germanic, and most of the current techniques of historical linguistics (e.g. the comparative method and the method of internal reconstruction) were developed as a result.
Scholars estimate that PIE may have been spoken as a single language (before divergence began) around 3700 BC, though estimates by different authorities can vary by more than a millennium. The most popular hypothesis for the origin and spread of the language is the Kurgan hypothesis, which postulates an origin in the Pontic-Caspian steppe of Eastern Europe.
The existence of PIE was first postulated in the 18th century by Sir William Jones, who observed the similarities between Sanskrit, Ancient Greek, and Latin. By the early 20th century, well-defined descriptions of PIE had been developed that are still accepted today (with some refinements). The largest developments of the 20th century have been the discovery of Anatolian and Tocharian languages and the acceptance of the laryngeal theory. The Anatolian languages have also spurred a major re-evaluation of theories concerning the development of various shared Indo-European language features and the extent to which these features were present in PIE itself.
PIE is thought to have had a complex system of morphology that included inflections (suffixing of roots, as in who, whom, whose), and ablaut (vowel alterations, as in sing, sang, sung). Nouns used a sophisticated system of declension and verbs used a similarly sophisticated system of conjugation.
Relationships to other language families, including the Uralic languages, have been proposed but remain controversial.
There is no written evidence of Proto-Indo-European, so all knowledge of the language is derived by reconstruction from later languages using linguistic techniques such as the comparative method and the method of internal reconstruction.
Discovery and reconstruction 
Historical and geographical setting 
There are several competing hypotheses about when and where PIE was spoken. The Kurgan hypothesis is "the single most popular" model, postulating that the Kurgan culture of the Pontic steppe were the hypothesized speakers of the reconstructed Proto-Indo-European language. Alternative theories such as the Anatolian urheimat[page needed] and Armenian hypothesis have also gained acceptance.
The satemization process that resulted in the Centum-Satem isogloss probably started as early as the 4th millennium BC and the only thing known for certain is that the proto language must have been differentiated into unconnected daughter dialects by the late 3rd millennium BC.
Mainstream linguistic estimates of the time between PIE and the earliest attested texts (ca. nineteenth century BC; see Kültepe texts) range around 1,500 to 2,500 years, with extreme proposals diverging up to another 100% on either side. Proposed models include:
- the 4th millennium BC (excluding the Anatolian branch) in Armenia, according to the Armenian hypothesis (proposed in the context of Glottalic theory);
- the 5th millennium BC (4th excluding the Anatolian branch) in the Pontic-Caspian steppe, according to Marija Gimbutas's Kurgan hypothesis;
- the 6th millennium BC or later in Northern Europe according to Lothar Kilian's and, especially, Marek Zvelebil's models of a broader homeland;
- the 6th millennium BC in India, according to Koenraad Elst's Out of India model;
- the 7th millennium BC in Ariana/BMAC according to a number of scholars.[who?]
- the 7th millennium BC in Anatolia (the 5th, in the Balkans, excluding the Anatolian branch), according to Colin Renfrew's Anatolian hypothesis;
- the 7th millennium BC in Anatolia (6th excluding the Anatolian branch), according to glottochronological studies;[page needed]
- before the 10th millennium BC in the Paleolithic Continuity Theory.
Indo-European studies began with Sir William Jones making and propagating the observation that Sanskrit bore a certain resemblance to classical Greek and Latin. In The Sanscrit Language (1786) he suggested that all three languages had a common root, and that indeed they might further all be related, in turn, to Gothic and the Celtic languages, as well as to Persian.
His third annual discourse before the Asiatic Society on the history and culture of the Hindus (delivered on 2 February 1786 and published in 1788) with the famed "philologer" passage is often cited as the beginning of comparative linguistics and Indo-European studies. This is Jones' most quoted passage, establishing his tremendous find in the history of linguistics:
The Sanscrit language, whatever be its antiquity, is of a wonderful structure; more perfect than the Greek, more copious than the Latin, and more exquisitely refined than either, yet bearing to both of them a stronger affinity, both in the roots of verbs and the forms of grammar, than could possibly have been produced by accident; so strong indeed, that no philologer could examine them all three, without believing them to have sprung from some common source, which, perhaps, no longer exists; there 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.
This common source came to be known as Proto-Indo-European.
The classical phase of Indo-European comparative linguistics leads from Franz Bopp's Comparative Grammar (1833) to August Schleicher's 1861 Compendium and up to Karl Brugmann's Grundriss published from the 1880s. Brugmann's junggrammatic re-evaluation of the field and Ferdinand de Saussure's development of the laryngeal theory may be considered the beginning of "contemporary" Indo-European studies.
PIE as described in the early 20th century is still generally accepted today; subsequent work is largely refinement and systematization, as well as the incorporation of new information, such as the Anatolian and Tocharian branches unknown in the 19th century.
The laryngeal theory, in its early forms discussed since the 1880s, became mainstream after Jerzy Kuryłowicz's 1927 discovery of the survival of at least some of these hypothetical phonemes in Anatolian.
Julius Pokorny's landmark Indogermanisches etymologisches Wörterbuch ("Indo-European Etymological Dictionary", 1959) gave a detailed overview of the lexical knowledge accumulated up until that time, but neglected contemporary trends of morphology and phonology (including the laryngeal theory), and largely ignored Anatolian.
The generation of Indo-Europeanists active in the last third of the 20th century (such as Calvert Watkins, Jochem Schindler and Helmut Rix) developed a better understanding of morphology and, in the wake of Kuryłowicz's 1956 Apophonie, understanding of the ablaut. From the 1960s, knowledge of Anatolian became certain enough to establish its relationship to PIE; see also Indo-Hittite.
There is no direct evidence of PIE, because it was never written. All PIE sounds and words are reconstructed from later Indo-European languages using the comparative method and the method of internal reconstruction. An asterisk is used to mark reconstructed PIE words, such as *wódr̥ 'water', *ḱwṓn 'dog' (English hound), or *tréyes 'three (masculine)'. Many of the words in the modern Indo-European languages seem to have derived from such "protowords" via regular sound changes (e.g., Grimm's law).
As the Proto-Indo-European language broke up, its sound system diverged as well, according to various sound laws in the daughter languages. Notable among these are Grimm's law and Verner's law in Proto-Germanic, loss of prevocalic *p- in Proto-Celtic, reduction to h of prevocalic *s- in Proto-Greek, Brugmann's law and Bartholomae's law in Proto-Indo-Iranian, Grassmann's law independently in both Proto-Greek and Proto-Indo-Iranian, and Winter's law and Hirt's law in Balto-Slavic.
Relationships to other language families 
Proposed genetic connections 
Many higher-level relationships between Proto-Indo-European and other language families have been proposed, but these hypothesized connections are highly controversial. A proposal often considered to be the most plausible of these is that of an Indo-Uralic family, encompassing PIE and Uralic. The evidence usually cited in favor of this consists in a number of striking morphological and lexical resemblances. Opponents attribute the lexical resemblances to borrowing from Indo-European into Uralic. Frederik Kortlandt, while advocating a connection, concedes that "the gap between Uralic and Indo-European is huge", while Lyle Campbell, an authority on Uralic, denies any relationship exists.
Other proposals, further back in time (and proportionately less accepted), link Indo-European and Uralic with Altaic and the other language families of northern Eurasia, namely Yukaghir, Korean, Japanese, Chukotko-Kamchatkan, Nivkh, Ainu, and Eskimo–Aleut, but excluding Yeniseian (the most comprehensive such proposal is Joseph Greenberg's Eurasiatic), or link Indo-European, Uralic, and Altaic to Afro-Asiatic and Dravidian (the traditional form of the Nostratic hypothesis), and ultimately to a single Proto-Human family.
Etruscan shows some similarities to Indo-European, such as a genitive in -s. There is no consensus on whether these are due to a genetic relationship, borrowing, chance and sound symbolism, or some combination of these.
Proposed areal connections 
The existence of certain PIE typological features in Northwest Caucasian languages may hint at an early Sprachbund or substratum that reached geographically to the PIE homelands. This same type of languages, featuring complex verbs of which the current Northwest Caucasian languages might have been the sole survivors, was cited by Peter Schrijver to indicate a local lexical and typological reminiscence in western Europe pointing to a possible Neolithic substratum.
|Fricative||*s||*h₁, *h₂, *h₃|
Alternative notations: The aspirated stops are sometimes written as *bh, *dh, *ǵh, *gh, *gʷh; for the palatals, *k̑, *g̑ are often used; and *i̯, *u̯ can replace *j, *w.
IPA note: The notation used above is traditional in Indo-European studies, but should not necessarily be interpreted as the corresponding IPA values. Most saliently, *y is traditionally used to represent IPA /j/, not any sort of front-rounded vowel. In addition, the traditional names and symbols for the dorsals and laryngeals should not be taken as more than a vague suggestion of their actual values.
The following are the main characteristics of PIE consonants:
- PIE had a large number of stops, but few fricatives. The traditional (pre-laryngeal) reconstruction included only one fricative, /s/; however, the modern theory includes three additional fricatives, commonly known as laryngeals and assumed to have been pronounced far back in the mouth (i.e. velar, uvular[disambiguation needed], pharyngeal and/or glottal[disambiguation needed]). Laryngeals disappeared from all PIE languages except (to some extent) the Anatolian languages, but reveal themselves in their effects on nearby sounds. For example, short *e adjacent to *h₂ and *h₃ is colored to *a and *o, respectively, and short vowels preceding a laryngeal are usually lengthened. The exact pronunciation of the laryngeals is disputed; some linguists have even asserted that /*h₁/ might not have been a fricative at all, but a glottal stop.
- Both the number of dorsal consonants (k-type sounds, i.e. stops pronounced in the back of the mouth) and their actual pronunciation are sources of controversy. In particular, the existence of the "plain velar" series as phonemically distinct consonants has long been a source of contention. The traditional theory, which most linguists still adhere to, calls for three series of dorsals, traditionally termed "palatovelar", "plain velar" and "labiovelar". These terms should be viewed as notional rather than expressing any particular commitment to the actual pronunciation of the sounds: in particular, a number of linguists[page needed] have argued that the pronunciations implied by the traditional terms are unlikely given later developments, and that a more likely pronunciation was as plain velar, uvular, and labialized velar, respectively. The dispute over the status of the traditional plain velar series concerns the fact that this is the least-common series; is mostly confined to specific environments (e.g. before /a/ or /r/), and the palatovelar series is not often found in these same environments; and is reflected identically to one of the other two series in all, or nearly all, of the daughters. This has led some linguists to reconstruct only two series, with the distinction between "palatovelar" and "plain velar" a secondary distinction that arose as an areal feature in some of the daughters (especially the "satem" languages).
- PIE is traditionally reconstructed with three types of voicings for its stops: voiceless, voiced, and breathy-voiced (traditionally termed "voiced aspirated"). This is typologically uncommon, and in fact the reconstructed breathy-voiced series appears as such only in Indo-Aryan languages. Thus, some linguists have proposed the glottalic theory, which proposes a very different reconstruction of these three series. However, this theory is not widely accepted today.
- A notable characteristic is that the resonants /r/, /l/, /m/, /n/, /y/ and /w/ could appear as vowels as well as consonants, specifically when not adjacent to another vowel. The same is usually held to be true of the laryngeals, as well. This has led to some dispute as to whether PIE should be reconstructed with phonemes /i/ and /u/, or whether these should be considered allophones of /y/ and /w/; however, there is some evidence that /i/, at least, could occur in the same environments as /y/.
- Short vowel phonemes: *e, *o.
- Long vowel phonemes: *ē, *ō. Sometimes a colon (:) is employed instead of the macron sign to indicate vowel length (*e:, *o:).
- Diphthongs: *ei, *eu, *ēi, *ēu, *oi, *ou, *ōi, *ōu. Diphthongs are sometimes understood as combinations of a vowel plus a semivowel, e. g. *ey or *ei̯ instead of *ei.[page needed]
- Vocalic allophones: *a (underlying *e adjacent to *h₂); *i, *u, *m̥, *n̥, *l̥, *r̥ (underlying resonant consonants when not adjacent to a vowel); *h̥₁, *h̥₂, *h̥₃ (underlying laryngeal consonants when not adjacent to a vowel).
- independent *a and possibly *ā
- independent *i and possibly *u
- phonemes or allophones due to compensatory lengthening triggered by laryngeal loss already in the proto-language (e.g. due to Stang's law), potentially including: *a, *ā (separate from possible independent occurrences); long variants of vocalic allophones (*m̥̄, *n̥̄, *l̥̄, *r̥̄, *ī, *ū); a-quality diphthongs (*ai, *au, *āi, *āu, separate from possible independent occurrences)
- possibly, rare phonemes *ī, *ū.
The potential existence of independent *a (and possibly *ā) is a particular source of dispute. It is often suggested that all *a were earlier derived from an *e preceded or followed by *h₂, but Mayrhofer, Ringe[page needed] and a number of others have argued that PIE did in fact have the phoneme *a (and possibly also *ā) independent of h₂.
PIE had a free pitch accent, 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, or between nominative/accusative and oblique cases of a nominal paradigm). The location of the pitch accent is closely associated with ablaut variations, especially between normal-grade vowels (/e/ and /o/) and zero-grade vowels (i.e. lack of a vowel). 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 PIE languages.
PIE was an inflected language, in which the grammatical relationships between words were signaled through inflectional morphemes (usually endings). The roots of PIE are basic morphemes carrying a lexical meaning. By addition of suffixes, they form stems, and by addition of desinences (usually endings), these form grammatically inflected words (nouns or verbs). PIE roots are understood to be predominantly monosyllabic with a basic shape CvC(C). This basic root shape is often altered by ablaut. Roots which appear to be vowel initial are believed by many scholars to have originally begun with a set of consonants, later lost in all but the Anatolian branch, called laryngeals (usually indicated *H, and often specified with a subscript number *h₁, *h₂, *h₃). Thus a verb form such as the one reflected in Latin agunt, Greek ἄγουσι (ágousi), Sanskrit ajanti would be reconstructed as *h₂eǵ-onti, with the element *h₂eǵ- constituting the root per se.
An important component of PIE morphophonology is the variation in vowels commonly termed ablaut, which occurred both within inflectional morphology (among different members of a nominal or verbal paradigm) and derivational morphology (between, for example, a verb and an associated verbal noun). Ablaut in PIE was closely associated with the position of the accent; for example, the alternation found in Latin est, sunt reflects PIE *h₁és-ti, *h₁s-ónti. However, it is not possible to derive either one directly from the other. The primary ablaut variation was between normal grade or full grade (*/e/ and */o/), lengthened grade (*/ē/ and */ō/), and zero grade (lack of a vowel, which triggered the vocalic allophones of nearby resonants). The normal grade is often characterized as e-grade or o-grade depending on the particular vowel involved. Ablaut occurred both in the root and the ending. Originally, morphological categories were distinguished both by ablaut variations and different endings, but the decay of endings has led some languages to use ablaut alone to distinguish grammatical categories, as in the Modern English words sing, sang, sung, originally reflecting a pre-Proto-Germanic sequence *sengw-, *songw-, *sngw-. Some scholars[who?] believe that the inflectional affixes of Indo European reflect ablaut variants, usually zero-grade, of older PIE roots. Often the zero-grade appears where the word's accent has shifted from the root to one of the affixes.
Proto-Indo-European nouns were declined for eight or nine cases (nominative, accusative, genitive, dative, instrumental, ablative, locative, vocative, and possibly a directive or allative). There were three genders: masculine, feminine, and neuter.
There are two major types of declension, thematic and athematic. Thematic nominal stems are formed with a suffix *-o- (in vocative *-e) and the stem does not undergo ablaut. The athematic stems are more archaic, and they are classified further by their ablaut behaviour (acrostatic, proterokinetic, hysterokinetic and amphikinetic, after the positioning of the early PIE accent in the paradigm).
PIE pronouns are difficult to reconstruct owing to their variety in later languages. This is especially the case for demonstrative pronouns. PIE had personal pronouns in the first and second person, but not the third person, where demonstratives were used instead. The personal pronouns had their own unique forms and endings, and some had two distinct stems; this is most obvious in the first person singular, where the two stems are still preserved in English I and me. According to Beekes,[page needed] there were also two varieties for the accusative, genitive and dative cases, a stressed and an enclitic form.
|Personal pronouns (Beekes)|
|First person||Second person|
|Accusative||*h₁mé, *h₁me||*nsmé, *nōs||*twé||*usmé, *wōs|
|Genitive||*h₁méne, *h₁moi||*ns(er)o-, *nos||*tewe, *toi||*yus(er)o-, *wos|
|Dative||*h₁méǵʰio, *h₁moi||*nsmei, *ns||*tébʰio, *toi||*usmei|
As for demonstratives, Beekes tentatively reconstructs a system with only two pronouns: *so / *seh₂ / *tod "this, that" and *h₁e / *(h₁)ih₂ / *(h₁)id "the (just named)" (anaphoric). He also postulates three adverbial particles *ḱi "here", *h₂en "there" and *h₂eu "away, again", from which demonstratives were constructed in various later languages.
The Indo-European verb system is complex and, like the noun, exhibits a system of ablaut. The most basic categorization for the Indo-European verb was grammatical aspect. Verbs were classed as stative (verbs that depict a state of being), imperfective (verbs depicting ongoing, habitual or repeated action) or perfective (verbs depicting a completed action or actions viewed as an entire process). Verbs have at least four moods (indicative, imperative, subjunctive and optative, as well as possibly the injunctive, reconstructible from Vedic Sanskrit), two voices (active and mediopassive), as well as three persons (first, second and third) and three numbers (singular, dual and plural). Verbs were also marked by a highly developed system of participles, one for each combination of tense and mood, and an assorted array of verbal nouns and adjectival formations.
The following table shows two possible reconstructions of the PIE verb endings. Sihler's reconstruction largely represents the current consensus among Indo-Europeanists, while Beekes' is a radical rethinking of thematic verbs; although not widely accepted, it is included to show an example of more far-reaching recent research.
|Sihler (1995)[page needed]||Beekes (1995)[page needed]|
The Proto-Indo-European numerals are generally reconstructed as follows:
|three||*trei- (full grade) / *tri- (zero grade)||*treies|
|four||*kʷetwor- (o-grade) / *kʷetur- (zero grade)
(see also the kʷetwóres rule)
|six||*s(w)eḱs; originally perhaps *weḱs||*(s)uéks|
|eight||*oḱtō, *oḱtou or *h₃eḱtō, *h₃eḱtou||*h₃eḱteh₃|
|twenty||*wīḱm̥t-; originally perhaps *widḱomt-||*duidḱmti|
|thirty||*trīḱomt-; originally perhaps *tridḱomt-||*trih₂dḱomth₂|
|forty||*kʷetwr̥̄ḱomt-; originally perhaps *kʷetwr̥dḱomt-||*kʷeturdḱomth₂|
|fifty||*penkʷēḱomt-; originally perhaps *penkʷedḱomt-||*penkʷedḱomth₂|
|sixty||*s(w)eḱsḱomt-; originally perhaps *weḱsdḱomt-||*ueksdḱomth₂|
|seventy||*septm̥̄ḱomt-; originally perhaps *septm̥dḱomt-||*septmdḱomth₂|
|eighty||*oḱtō(u)ḱomt-; originally perhaps *h₃eḱto(u)dḱomt-||*h₃eḱth₃dḱomth₂|
|ninety||*(h₁)newn̥̄ḱomt-; originally perhaps *h₁newn̥dḱomt-||*h₁neundḱomth₂|
|hundred||*ḱm̥tom; originally perhaps *dḱm̥tom||*dḱmtóm|
Lehmann believes that the numbers greater than ten were constructed separately in the dialects groups and that *ḱm̥tóm originally meant "a large number" rather than specifically "one hundred".
Many particles could be used both as adverbs and postpositions, like *upo "under, below". The postpositions became prepositions in most daughter languages. Other reconstructible particles include negators (*ne, *mē), conjunctions (*kʷe "and", *wē "or" and others) and an interjection (*wai!, an expression of woe or agony).
Sample texts 
As PIE was conjectured to be spoken by a prehistoric society, no genuine sample texts are available, but since the 19th century modern scholars have made various attempts to compose example texts for purposes of illustration. These texts are educated guesses at best; Calvert Watkins in 1969 observes that in spite of its 150 years' history, comparative linguistics is not in the position to reconstruct a single well-formed sentence in PIE. Because of this and other similar objections based on Pratishakyas, such texts are of limited use in getting an impression of what a coherent utterance in PIE might have sounded like.
Published PIE sample texts:
- Schleicher's fable (Avis akvasas ka) by August Schleicher (1868), modernized by Hermann Hirt (1939) and Winfred Lehmann and Ladislav Zgusta (1979)
- The king and the god (rēḱs deiwos-kʷe) by S. K. Sen, E. P. Hamp et al. (1994)
In popular culture 
Daughter language groupings 
Generally accepted subfamilies (clades) 
- Proto-Albanian language
- Proto-Anatolian language
- Proto-Armenian language
- Proto-Balto-Slavic language
- Proto-Celtic language
- Proto-Germanic language
- Proto-Greek language
- Proto-Indo-Iranian language
- Proto-Italic language
- Proto-Tocharian language
Marginally attested languages 
These include languages that do not appear to be members of any of the above families, but which are so poorly attested that proper classification of them is not possible. Of these languages, Phrygian is easily the best-attested.
- Phrygian language
- Dacian language
- Thracian language
- Illyrian language
- Venetic language
- Messapic language
- Ancient Macedonian language
- Lusitanian language
All of the above languages except for Lusitanian (which occurs in the area of modern Portugal) occur in or near the Balkan peninsula, and have been collectively termed the "Paleo-Balkan languages". This is a purely geographic grouping and makes no claims about the relatedness of the languages to each other as compared with other Indo-European languages.
Hypothetical clades 
See also 
- Mallory 1989, p. 185: ‘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 Encyclopaedia Britannica and the Grand Dictionnaire Encyclopédique Larousse.’
- Strazny 2000, p. 163: "The single most popular proposal is the Pontic steppes (see the Kurgan hypothesis)..."
- Anthony, David W (2007). The Horse, the Wheel, and Language: How Bronze-Age Riders from the Eurasian Steppes Shaped the Modern World. Princeton University Press. ISBN 0-691-05887-3.
- Bouckaert et al. 2012.
- Kortlandt, Frederik, The spread of the Indo-Europeans (PDF), NL, "...the satemization process can be dated to the last centuries of the fourth millennium"
- Gray, Russell D; Atkinson, Quentin D (27 November 2003), "Language-tree divergence times support the Anatolian theory of Indo-European origin" (PDF), Nature (NZ: Auckland) (426): 435–39
- Bouckaert et al. 2012, p. 957.
- Kortlandt, Frederik (1993), General linguistics and Indo-European reconstruction (PDF), NL
- Kortlandt, Frederik (1989), The spread of the Indo-Europeans (PDF), NL
- Keltisch en de buren: 9000 jaar taalcontact (PDF) (in Dutch), NL: University of Utrecht, March 2007
- Huld, Martin E (1997), "Satəm, Centum, and Hokum", in Adams, Douglas Q, Festschrift for Eric P. Hamp, pp. 115–38
- Clackson 2007, p. 52.
- Ringe 2006.
- Rix 2001.
- Mayrhofer 1986, pp. 170 ff.
- Fortson 2004, p. 102.
- Beekes 1995.
- Sihler 1995.
- Sihler 1995, pp. 402–24.
- Lehmann, Winfried P (1993). Theoretical Bases of Indo-European Linguistics. London: Routledge. pp. 252–55. ISBN 0-415-08201-3.
- "Language Log » Proto-Indo-European in Prometheus?". Languagelog.ldc.upenn.edu. 2012-06-08. Retrieved 2013-03-12.
Introductory works 
- Beekes, Robert SP (1995), Comparative Indo-European Linguistics: An Introduction, Amsterdam: John Benjamins, ISBN 90-272-2150-2 (Europe), ISBN 1-55619-504-4 (US)
- Clackson, James (2007), Indo-European Linguistics: An Introduction, Cambridge Textbooks in Linguistics, Cambridge: Cambridge University Press, ISBN 0-521-65313-4
- Fortson, Benjamin W., IV (2004), Indo-European Language and Culture, Blackwell Publishing, ISBN 1-4051-0316-7.
- Lehmann, Winfred (1996) , Theoretical Bases of Indo-European Linguistics (new ed.), Routledge, ISBN 0-415-13850-7
- Mallory, JP; Adams, DQ (2006), The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World, Oxford: Oxford University Press, ISBN 9780199296682
- Meier-Brügger, Michael (2003), Indo-European Linguistics, New York: de Gruyter, ISBN 3-11-017433-2
- Szemerényi, Oswald (1996), Introduction to Indo-European Linguistics, Oxford
Major technical handbooks on Proto-Indo-European 
- Mayrhofer, Manfred (1986), Indogermanische Grammatik, i/2: Lautlehre, Heidelberg: Winter
- Pokorny, Julius (2005) [1948–59], Indogermanisches etymologisches Wörterbuch (5 ed.), Francke, ISBN 3-7720-0947-6
- Rix, Helmut (2001), Lexikon der indogermanischen Verben (2 ed.), Dr. Ludwig Reichert Verlag, ISBN 3-89500-219-4
Major technical works on daughter languages and Proto-Indo-European 
- Ringe, Don (2006), From Proto-Indo-European to Proto-Germanic, Oxford University Press, ISBN 978-0-19-955229-0
- Sihler, Andrew L (1995), New Comparative Grammar of Greek and Latin, Oxford: Oxford University Press, ISBN 0-19-508345-8
Other major technical works on daughter languages 
- Buck, Carl Darling (1933). Comparative Grammar of Greek and Latin. Chicago: University of Chicago Press. ISBN 0-226-07931-7.
- Hoffner, Harry A., Jr.; Melchert, H. Craig (2008). A Grammar of the Hittite Language, 1: Reference Grammar. Eisenbrauns. ISBN 1-57506-119-8.
- Thurneysen, Rudolf (1990 (1946)). A Grammar of Old Irish (Rev Enl Re ed.). Colton Book Imports. ISBN 1-85500-161-6.
- Whitney, William Dwight (1889). Sanskrit Grammar. Harvard University Press. ISBN 81-208-0621-2 (India), ISBN 0-486-43136-3 (Dover, US) Check
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|Look up Appendix:List of Proto-Indo-European roots in Wiktionary, the free dictionary.|
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