Proto-Indo-European phonology

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The phonology of the Proto-Indo-European language (PIE) has been reconstructed by linguists, based on the similarities and differences among current and extinct Indo-European languages. Because PIE was not written, linguists must rely on the evidence of its earliest attested descendants, such as Hittite, Sanskrit, Ancient Greek and Latin, to reconstruct its phonology.

The reconstruction of abstract units of PIE phonological systems (i.e. segments, or phonemes in traditional phonology) is mostly fairly uncontroversial, although areas of dispute remain. Their phonetic interpretation is more difficult to establish; this pertains especially to the vowels, the so-called laryngeals, and the voiced stops.

Phonemic inventory

Proto-Indo-European is traditionally reconstructed to have used the following phonemes. See the article on Indo-European sound laws for a summary of how these phonemes reflected in the various Indo-European languages.


Labial Coronal Dorsal Laryngeal
palatal plain labial
Nasals *m *n
Stops voiceless *p *t * *k *
voiced (*b) *d *ǵ *g *
aspirated * * *ǵʰ * *gʷʰ
Fricatives *s *h₁, *h₂, *h₃
Liquids *r, *l
Semivowels *y *w

The table gives the most common notation in modern publications; variant transcriptions are given below. Raised ʰ stands for aspiration, and raised ʷ for labialization. The *y corresponds to the palatal semivowel whose IPA transcription is [j] (and not to IPA [y]).

Stop series

Formerly, four stop series were reconstructed: voiceless unaspirated and aspirated, and voiced unaspirated and aspirated (e.g. *t, *tʰ, *d, *dʰ). The voiceless aspirated stops, however, came to be reinterpreted as sequences of stop plus laryngeal, and so the standard reconstruction now includes only three of those series, with the traditional phonetic descriptions of voiceless, voiced and voiced aspirated. However, a system of this type is not found in any descendant language (Sanskrit had all three, but along with a fourth voiceless aspirated series), and is vanishingly rare in any recorded languages. The absence or rarity of */b/ (see below) is also unusual. Additionally, PIE roots have a constraint which prohibits roots mixing voiceless and voiced aspirate stops, as well as roots containing two voiced stops. These facts have led some scholars to reassess this part of the reconstruction, replacing the voiced stops by glottalized and the voiced aspirated stops by plain voiced. Direct evidence for glottalization is limited, but there is some indirect evidence, including Winter's law in Balto-Slavic, and in the fact that the voiceless consonants and the voiced aspirate consonants develop in parallel in Germanic, with both becoming fricatives while the glottalized (plain voiced in traditional theory) consonants remain stops.

Labials and coronals

PIE */p/, */b/, */bʰ/ are grouped with the cover symbol P. The phonemic status of */b/ is disputed: it seems not to appear as an initial consonant (except in a few dubious roots such as *bel-, noted below), while reconstructed roots with internal */b/ are usually restricted to Western branches, casting doubt on their validity for PIE.[1]

Some have attempted to explain away the few roots with */b/ as a result of later phonological developments.[2] Suggested such developments include

  • *ml- > *bl-, connecting the dubious root *bel- 'power, strength' (> Sanskrit bálam, Ancient Greek beltíōn) with mel- in Latin melior, and *h₂ebl-/*h₂ebōl 'apple' with a hypothetical earlier form *h₂eml-, which is in unmetathesized form attested in another reconstructible PIE word for apple, *méh₂lom (> Hittite maḫla-, Latin mālum, Ancient Greek mēlon).
  • In PIE *ph₃ the *p regularly gives *b; for example, the reduplicated present stem of *peh₃- 'to drink' > *pi-ph₃- > Sanskrit píbati.

At best, PIE */b/ remains a highly marginal phoneme.

The standard reconstruction identifies three coronal, or dental, stops: */t/, */d/, */dʰ/. They are symbolically grouped with the cover symbol T.


According to the traditional reconstruction, such as the one laid out in Brugmann's Grundriss der vergleichenden Grammatik der indogermanischen Sprachen more than a century ago, three series of velars are reconstructed for PIE:

  • "Palatovelars" (or simply "palatals"), */ḱ/, */ǵ/, */ǵʰ/ (also transcribed */k'/, */g'/, */g'ʰ/ or */k̑/, */g̑/, */g̑ʰ/ or */k̂/, */ĝ/, */ĝʰ/).
  • "Plain velars" (or "pure velars"), */k/, */g/, */gʰ/.
  • Labiovelars, */kʷ/, */gʷ/, */gʷʰ/ (also transcribed */k/, */g/, */gu̯h/). The raised ʷ or stands for labialization (lip rounding) accompanying the velar articulation.

The actual pronunciation of these sounds in PIE is not certain. One current idea is that the "palatovelars" were in fact simple velars, i.e. *[k], *[g], *[gʰ], while the "plain velars" were pronounced farther back, perhaps as uvular consonants, i.e. *[q], *[ɢ], *[ɢʰ].[3] If the labiovelars were just labialized forms of the "plain velars', they would then have been pronounced *[qʷ], *[ɢʷ], *[ɢʷʰ]. For arguments in support of this view, see Centum and satem languages: Different realizations.

Another theory is that there may have been only two series (plain velar and labiovelar) in PIE, with the palatalized velars arising originally as a conditioned sound change in satem languages. See Centum and satem languages: Only two velar series.

The satem languages merged the labiovelars *kʷ, *gʷ, *gʷʰ with the plain velar series *k, *g, *gʰ, while the palatovelars *ḱ, *ǵ, *ǵʰ became sibilant fricatives or affricates of various types, depending on the individual language. In some phonological conditions depalatalization occurred, yielding what appears to be a centum reflex in a satem language. For example, in Balto-Slavic and Albanian, palatovelars were depalatalized before resonants unless the latter were followed by a front vowel. The reflexes of the labiovelars are generally indistinguishable from those of the plain velars in satem languages, but there are some words where the lost labialization has left a trace, such as by u-coloring a following vowel.

The centum group of languages, on the other hand, merged the palatovelars *ḱ, *ǵ, *ǵʰ with the plain velar series *k, *g, *gʰ, while the labiovelars *kʷ, *gʷ, *gʷʰ were kept distinct. Analogous to the depalatalization of the satem languages, the centum languages show delabialisation of labiovelars when adjacent to *w (or its allophone *u), according to a rule known as the boukólos rule.


The only certain PIE fricative phoneme */s/ was a strident sound, whose phonetic realization could possibly range from [s] to palatalized [ɕ] or [ʃ]. It had a voiced allophone *z that emerged by assimilation in words such as *nisdós 'nest', and which later became phonemicized in some daughter languages. Some PIE roots have variants with *s appearing initially: such *s is called s-mobile.

The "laryngeals" may have been fricatives, but there is no consensus as to their phonetic realization.


The phonemes */h₁/, */h₂/, */h₃/, with cover symbol H also denoting "unknown laryngeal" (or ə₁, ə₂, ə₃ and ə), stand for three "laryngeal" phonemes. One should note that the term laryngeal as a phonetic description is out of date, retained only because its usage has become standard in the field.

The phonetic values of the laryngeal phonemes are disputable; various suggestions for their exact phonetic value have been made, ranging from cautious claims that all that can be said with certainty is that */h₂/ represented a fricative pronounced far back in the mouth, and that *h₃ exhibited lip-rounding up to more definite proposal; e.g. Meier-Brügger writes that realizations of *h₁ = [h], *h₂ = [χ] and *h₃ = [ɣ] or [ɣʷ] "are in all probability accurate".[4] Other commonly cited speculations for *h₁ *h₂ *h₃ are ʔ ʕ ʕʷ (e.g. Beekes) and x χ~ħ xʷ.[who?] It is sometimes claimed[citation needed] that *h₁ may have been two consonants, ʔ and h, that fell together. A consensus seems to be emerging[citation needed], however, that *h₁ is unlikely to have been a glottal stop /ʔ/, as all three laryngeals pattern similarly to each other and to fricatives in other languages (and similarly to PIE /s/, the only other fricative); in contrast, Simon (2013)[5] has argued that the Hieroglyphic Luwian sign *19 stood for /ʔa/ (distinct from /a/) and represents the reflex of */h₁/. It is possible, however, that all three laryngeals ultimately fell together as a glottal stop in some languages. Evidence for this development in Balto-Slavic comes from the eventual development of post-vocalic laryngeals into a register distinction commonly described as "acute" (vs. "circumflex" register on long vocalics not originally closed by a laryngeal) and marked in some fashion on all long syllables, whether stressed or not; furthermore, in some circumstances original acute register is reflected by a "broken tone" (i.e. glottalized vowel) in modern Latvian.

The schwa indogermanicum symbol ə is sometimes used for a laryngeal between consonants, in a "syllabic" position.


In a phonological sense, sonorants in Proto-Indo-European were those segments that could appear both in the syllable nucleus (i.e. they could be syllabic) and out of it (i.e. they could be non-syllabic). PIE sonorants are the liquids, nasals and glides: */r/, */l/, */m/, */n/, */y/ (or *i̯), */w/ (or *u̯), all grouped with the cover symbol R.

All of them had allophones in a syllabic position, which is generally between consonants, word-initially before consonants and word-finally after a consonant. They are marked as: *r̥, *l̥,*m̥, *n̥, *i, *u. One should note that, even though *i and *u were phonetically certainly vowels, phonologically they were syllabic sonorants.


Some of the changes undergone by the PIE consonants in daughter languages are the following:

  • Proto-Celtic, Albanian, Proto-Balto-Slavic and Proto-Iranian merged the voiced aspirated series */bʰ/, */dʰ/, */ǵʰ/, */gʰ/, */gʷʰ/ with the plain voiced series */b/, */d/, */ǵ/, */g/, */gʷ/. (In Proto-Balto-Slavic this postdated Winter's law. Proto-Celtic retains the distinction between */gʷʰ/ and */gʷ/ - the former became */gw/ while the latter became */b/.)
  • Proto-Germanic underwent Grimm's law, changing voiceless stops into fricatives, devoicing unaspirated voiced stops, and fricativizing and deaspirating voiced aspirates.
  • Grassmann's law (Tʰ-Tʰ > T-Tʰ, e.g. dʰi-dʰeh₁- > di-dʰeh₁-) and Bartholomae's law (TʰT > TTʰ, e.g. budʰ-to- > bud-dʰo-) describe the behaviour of aspirates in particular contexts in some early daughter languages.

Sanskrit, Greek, and Germanic, along with Latin to some extent, are the most important for reconstructing PIE consonants, as all of these languages keep the three series of stops (voiceless, voiced and voiced-aspirated) separate. In Germanic, Verner's law and changes to labiovelars (especially outside of Gothic) obscure some of the original distinctions; but on the other hand, Germanic is not subject to the assimilations of Grassmann's law, which affects both Greek and Sanskrit. Latin also keeps the three series separate, but largely obscures the distinctions among voiced-aspirated consonants in initial position (all except /gʰ/ become /f/) and collapses many distinctions in medial position. Greek is especially important for reconstructing labiovelars, as other languages tend to delabialize them in many positions.

Anatolian and Greek are the most important languages for reconstructing the laryngeals. Anatolian directly preserves many laryngeals, while Greek preserves traces of laryngeals in positions (e.g. at the beginning of a word) where they disappear in many other languages, and reflects each laryngeal different from the others (the so-called triple reflex) in most contexts. Balto-Slavic languages are sometimes important in reconstructing laryngeals, since they are fairly directly represented in the distinction between "acute" and "circumflex" vowels. Old Avestan faithfully preserves numerous relics (e.g. laryngeal hiatus, laryngeal aspiration, laryngeal lengthening) triggered by ablaut alternations in laryngeal-stem nouns, but the paucity of the Old Avestan corpus prevents it from being more useful. Vedic Sanskrit preserves the same relics rather less faithfully, but in greater quantity, making it sometimes useful.



It is disputed how many vowels Proto-Indo-European (PIE) had, as well as what counts as a "vowel" in that language. It is generally agreed that at least four vowel segments existed, normally denoted as */e/, */o/, */ē/ and */ō/. All of these vowels are morphologically conditioned to varying extents. The two long vowels are less common than the short vowels and their morphological conditioning is especially strong, suggesting that in an earlier stage there may not have been a length opposition, and a system with as few as two vowels (or even only one vowel, according to some researchers) may have existed.

In addition, the surface vowels *i and *u were extremely common, and syllabic sonorants *r̥, *l̥, *m̥, *n̥ existed. All of these alternate in a syllabic position with sonorant consonants *y, *w, *r, *l, *m, *n. For example, the root of the PIE word *yugóm ('yoke') with a *u also appears in the verb *yewg- ('to yoke, harness, join') with *w. Similarly, the PIE word *dóru ('tree, wood') is reconstructed with genitive singular *dréws and dative plural *drúmos. Some authors (e.g. Ringe (2006)) have argued that there is strong evidence for reconstructing a non-alternating phoneme *i in an addition to an alternating phoneme *y, as well as weaker evidence for a non-alternating phoneme *u.

In addition, all daughter Indo-European languages have a segment */a/, and those languages with long vowels generally have long /aː/ /iː/ /uː/. Up until the mid-20th century, PIE was reconstructed with all of these vowels. Modern versions incorporating the laryngeal theory, however, tend to view these vowels as later developments of sounds that should be reconstructed in PIE as laryngeals *h₁, *h₂, h₃. For example, what used to be reconstructed as PIE is now reconstructed as *eh₂; *ī, *ū are now reconstructed as */iH/ */uH/, where *H represents any laryngeal; and *a has various origins, among which are a "syllabic" [H̥] (i.e. any laryngeal when not adjacent to a vowel, or an *e next to the "a-coloring" laryngeal *h₂e. (Note that although these cases may have phonetically contained the vowel [a] in spoken PIE, it would in fact be an allophone of *e and not an independent phoneme.) Some researchers, however, have argued that an independent phoneme *a must be reconstructed that cannot be traced back to any laryngeal.

Any of the sonorant consonants can comprise the second part of a complex syllable nucleus, i.e. they can form diphthongs with any of the vowels *e, *o, *ē, *ō; e.g. *ey, *oy, *ēy, *ōy, */ew/, */ow/, */em/, */en/, etc.

It is generally accepted that PIE did not allow vowels word-initially; those vowel-initial words in earlier reconstructions are now usually reconstructed as beginning with one of the three laryngeals, which in all daughter languages except Hittite disappeared initially before a vowel (after coloring it if possible).

Lengthened vowels

In certain morphological (e.g., as a result of Proto-Indo-European ablaut) and phonological conditions (e.g. in the last syllable of nominative singular of a noun ending on sonorant, in root syllable in sigmatic aorist etc.; cf. Szemerényi's law, Stang's law) vowels *e and *o would lengthen, yielding respective lengthened-grade variants. Basic, lexical forms of words in PIE contain therefore only short vowels; on the basis of well-established morphophonological rules forms with long vowels *ē and *ō appear.

Lengthening of vowels may have been a phonologically conditioned change in Early Proto-Indo-European, but at the period just before the dissolution of Proto-Indo-European speaking community, which is usually reconstructed, it is not possible to phonologically predict the appearance of all long vowels, because the phonologically justified resulting long vowels have begun to spread analogically to other forms in which they were not phonologically justified. Hence, the prosodically long */e/ in *ph₂tḗr 'father' results by the application of Szemerényi's law, a synchronic phonological rule that operated within the PIE, but prosodically long */o/ in *pṓds 'foot' is analogically leveled.


It is possible that Proto-Indo-European had a few morphologically isolated words that contained the vowel *a, e.g. *dap- 'sacrifice' (Latin daps, Ancient Greek dapánē, Old Irish dúas); or appearing as a first part of a diphthong *ay, e.g. *laywos 'left' (Latin laevus, Ancient Greek laiós, OCS lěvъ). The phonemic status of *a has been fiercely disputed; for example Beekes[6] expressly concludes: There are thus no grounds for PIE phoneme *a, and the same conclusion is reached by his former student Alexander Lubotsky.[7] After the discovery of Hittite and the advent of laryngeal theory, basically every instance of previous *a could be reduced to the vowel *e either preceded or followed by the laryngeal *h₂ (rendering the previously reconstructed short and long *a, respectively). Against the possibility of PIE phoneme *a, that is even today held by some Indo-Europeanists, the following can be said: vowel *a does not participate in ablaut alternations (i.e. it does not alternate with other vowels, as the "real" PIE vowels *e, *o, *ē, *ō do), it makes no appearance in suffixes and endings, it appears in very confined set of positions (usually after initial *k, which could be the result of that phoneme being a-coloring—particularly likely if it was in fact uvular /q/) and the reflexes of words upon which *a is reconstructed are usually confined only to a few Indo-European languages (e.g. *bʰardʰéh₂ 'beard', which is confined to western and northern daughter families) which makes it possible to ascribe it to some late PIE dialectalism, or are of expressive character (e.g. the interjection *wai 'alas') thus not being suitable for comparative analysis, or are argued to have been borrowed from some other language which had phonemic *a (e.g. Proto-Semitic *θawru > PIE *táwros ('aurochs')).

However, others, like Mayrhofer,[8] argue that PIE did in fact have *a and phonemes independent of *h₂.


Ancient Greek reflects the original PIE vowel system most faithfully, with few changes to PIE vowels in any syllable; however, loss of certain consonants, especially */s/, */w/ and */y/, often triggers compensatory lengthening or contraction of vowels in hiatus, which can complicate reconstruction.

Sanskrit and Avestan merge */e/, */a/ and */o/ into a single vowel */a/ (with a corresponding merger in the long vowels), but reflect PIE length differences (especially due to ablaut) even more faithfully than Greek, and do not have the same issues with consonant loss that Greek does. Furthermore, */o/ can often be reconstructed through Brugmann's law, and */e/ through its palatalization of a preceding velar (see Proto-Indo-Iranian language).

Germanic languages show merger of long and short */a/ and */o/, as well as the merger of */e/ and */i/ in non-initial syllables, but (especially in the case of Gothic) are still important for reconstructing PIE vowels. Balto-Slavic languages are similar, again showing merger of short */a/ and */o/ (and for Slavic languages, also long */a/ and */o/).

Evidence from Anatolian and Tocharian can be important due to the archaism of these languages, but is often difficult to interpret; Tocharian, especially, has complex and far-reaching vowel innovations.

Italic languages and Celtic languages do not unilaterally merge any vowels, but have such far-reaching vowel changes (especially in the case of the Celtic languages, and the extreme vowel reduction of early Latin) that they are somewhat less useful for PIE. Albanian and Armenian are least useful, as they are attested relatively late, have borrowed heavily from other Indo-European languages, and have complex and ill-understood vowel changes.

In Proto-Balto-Slavic short PIE vowels were preserved, with the change of */o/ > */a/ as in Proto-Germanic. A separate reflex of the original *o or *a is however argued to have been retained in some environments as a lengthened vowel, due to the effect of Winter's law. Subsequently, Early Proto-Slavic merged *ō and *ā, which were retained in Baltic languages. Additionally, accentual differences in some Balto-Slavic languages indicate whether the post-PIE long vowel originated from a genuine PIE lengthened grade, or if it is a result of compensatory lengthening before a laryngeal.


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).

Generally, thematic nouns and verbs (those with a "thematic vowel" between root and ending, usually /e/ or /o/) had a fixed accent, which (depending on the particular noun or verb) could be either on the root or the ending. These words also had no ablaut variations within their paradigms. (However, accent and ablaut were still associated; for example, thematic verbs with root accent tended to have e-grade ablaut in the root, while those ending accent tended to have zero-grade ablaut in the root.) On the other hand, athematic nouns and verbs usually had mobile accent, with varied between strong forms, with root accent and full grade in the root (e.g. the singular active of verbs, and the nominative and accusative of nouns), and weak forms, with ending accent and zero grade in the root (e.g. the plural active and all forms of the middle of verbs, and the oblique cases of nouns). Some nouns and verbs, on the other hand, had a different pattern, with ablaut variation between lengthened and full grade and mostly fixed accent on the root; these are termed Narten stems. Additional patterns exist for both nouns and verbs. For example, some nouns (so-called acrostatic nouns, one of the oldest classes of noun) has fixed accent on the root, with ablaut variation between o-grade and e-grade, while hysterodynamic nouns have zero-grade root with a mobile accent that varies between suffix and ending, with corresponding ablaut variations in the suffix.

The accent is best preserved in Vedic Sanskrit and (in the case of nouns) Ancient Greek. It is also reflected to some extent in the accentual patterns of the Balto-Slavic languages (e.g. Latvian, Lithuanian and Serbo-Croatian). It is indirectly attested in a number of phenomena in other PIE languages, especially the Verner's law variations in the Germanic languages. In other languages (e.g. the Italic languages and Celtic languages) it was lost without a trace. Other than in Modern Greek, the Balto-Slavic languages and (to some extent) Icelandic, few traces of the PIE accent remain in any modern languages.

Phonological rules

A number of phonological rules can be reconstructed for Proto-Indo-European. Some of them are disputed to be valid for "PIE proper", and are claimed to be later innovations in some of the daughter branches. Some of these laws are:

  1. Bartholomae's law: TʰT > TTʰ
    Passive participle of *bʰewdʰ 'to learn, become aware of': *bʰudʰ-to- > *bʰud-dʰo- > (Grassmann's law) Sanskrit buddhá.
    Law has been preserved in Indo-Iranian branch where it operates as a synchronic rule. There are some traces of it in Ancient Greek and Germanic, and possibly in Latin.
  2. Dental assibilation: TT > TsT (a sequence of two dental stops had dental fricative */s/ inserted between them)
    *h₁ed-ti 'eats' > *h₁etsti > Hittite ezzi.
    This has been preserved in Hittite where cluster *tst is spelled as z (pronounced as [ts]). The cluster was often simplified to -ss- in the later descendants (Latin and Germanic among others).
  3. TK > KT > "Kþ": see Thorn clusters, below.
  4. Siebs' law: If s-mobile is added to the root that starts with voiced or aspirated stop, that stop is devoiced.
    *bʰr̥Hg- > Latin fragor, but *sbʰr̥Hg- > *sp(ʰ)r̥Hg- > Sanskrit sphūrjati
  5. Stang's law: *Vwm > *Vːm; i.e. */w/ disappears and the preceding vowel lengthens in the last syllable behind word-final */m/. Some also add rules: *Vmm > *Vːm and *Vh₂m > *Vːm; and also *Vyi > *Vːy.
    *dyéwm 'sky' (accusative singular) > *dyḗm > Sanskrit dyā́m, acc. sg. of dyaús
    *gʷowm 'cattle' (acc. sg.) > *gʷōm > Sanskrit gā́m, acc. sg. of gaús
    accusative singular of *dom- 'house' is *dṓm, not **dómm̥.
  6. Szemerényi's law: -VRs > VːR, -VRh₂ > VːR i.e. in word-final sequences of vowel, sonorant and */s/ or */h₂/ the fricative or laryngeal was dropped and the preceding vowel lengthened. This affected nominative singulars of numerous masculine and feminine nouns, as well as the nominoaccusative of neuter collectives.
    *ph₂tér-s 'father' > *ph₂tḗr > Ancient Greek patḗr, Sanskrit pitā́
  7. Laryngeal deletion rules: See below.

Thorn clusters

A problem in the reconstruction of PIE concerns some cognate sets in which Indo-Iranian sibilants in clusters with dorsals exceptionally correspond to coronal stops in certain other branches (particularly the Hellenic languages). 'Bear' and 'decaying' above are examples; some others are Sanskrit tákṣan 'artisan' vs. Greek téktōn 'carpenter', and Sanskrit kṣā́ḥ vs. Greek khthṓn both 'earth'. As was the case with the laryngeal theory, these cognate sets were first noted prior to the connection of Anatolian and Tocharian to PIE, and early reconstructions posited a new series of consonants to explain these correspondences. Brugmann 1897's systematic explanation augmented the PIE consonant system with a series of interdentals (nowhere directly attested) appearing only in clusters with dorsals, *kþ *kʰþʰ *gð *gʰðʰ. The use of the letter thorn led to the name "thorn cluster" for these groups.

Anatolian and Tocharian evidence suggests that the original form of the thorn clusters was in fact *TK: Hittite has tēkan, tagnās, dagān and Tocharian A tkaṃ, tkan- for case-forms of 'earth', so that the development outside Anatolian and Tocharian involved a metathesis. The conventional notations *þ *ð *ðʰ for the second elements of these metathesised clusters are still found, and some, including Fortson,[9] continue to hold to the view that interdental fricatives were involved at some stage of PIE.

Some possible outcomes of the metathesis are illustrated by the following roots:

  • *h₂ŕ̥tḱos 'bear' > *h₂ŕ̥ḱþos > Latin ursus, Ancient Greek árktos, Sanskrit ṛ́kṣas but Hittite ḫartaggas /ḫartkas/ without metathesis.
  • *dʰgʷʰítis 'decaying, decline, ruin' > *gʷʰþítis > Ancient Greek phthísis, Sanskrit kṣítis, perhaps Latin sitis
  • Metathetized and unmetathetized forms survive in different ablaut grades of the root *dʰégʷʰ ('burn' whence also English day) in Sanskrit, dáhati ('is being burnt') < *dʰégʷʰ-e- and kṣā́yat ('burns') < *dʰgʷʰ-éh₁-.

An alternative interpretation (e.g. Vennemann 1989, Schindler 1991 (informally and unpublished)[10]) identifies these segments as alveolar affricates [t͡s d͡z]. In this view, thorn clusters developed as TK > TsK > KTs and then variously in daughter languages; this has the advantage that the first change can be identified with the dental assibilation rule above, which is then broadened in application to affrication of dental stops before any stops. Melchert has interpreted the Cuneiform Luwian īnzagan- 'inhumation', probably [ind͡zɡan], from *h₁en dʰǵʰōm 'in the earth', as preserving the intermediate stage of this process.[9]

Laryngeal deletion rules

Once the laryngeal theory was developed, and the rules for sound change of laryngeals worked out, it was clear that there were a number of exceptions to the rules, in particular with regard to "syllabic" laryngeals (former "schwa indogermanicum") that occurred in non-initial syllables. It was long suggested that such syllabic laryngeals were simply deleted in certain of the daughters; this is based especially on the PIE word *dʰugh₂tér- "daughter", which appears in a number of branches (e.g. Germanic, Balto-Slavic) with no vowel in place of expected /a/ for "syllabic" /h₂/ (cf. English "daughter", Gothic daúhtar). With a better understanding of the role of ablaut, however, and a clearer understanding of which roots did and did not have laryngeals in them, it became clear that this suggestion cannot be correct. In particular, there are some cases where syllabic laryngeals in medial syllables delete in most or all daughter languages, and other cases where they do not delete even in Germanic and/or Balto-Slavic.

This has led to the more recent idea that PIE had a number of synchronic "laryngeal deletion" rules, where syllabic laryngeals in certain contexts were deleted even in the protolanguage. In the case of *dʰugh̥₂tér-, for example, it appears that PIE had an alternation between a "strong" stem *dʰugh̥₂tér- and a "weak" stem *dʰugtr-, where a deletion rule eliminated the laryngeal in the latter context but not the former one. Forms in daughter languages with the laryngeal (Ancient Greek thugátēr, Sanskrit duhitṛ) or without the laryngeal (Gothic dauhtar, Lithuanian duktė̃) are due to analogical generalization of one or the other protoforms.

This is a new area, and as a result there is no consensus on the number and nature of the deletion rules. A wide variety of rules have been proposed; Ringe (2006) identifies the following three as the most likely candidates (where C=any consonant, V=any vowel, H=any laryngeal, R=any resonant):

  1. A laryngeal in the sequence *oRHC was dropped. Example: *tórmos ('borehole') from *terh₁- "bore" (cf. Gk tórmos 'socket', OE þearm 'intestine'). This seems to have operated particularly in the thematic optative suffix *-oy-h₁-, which was reduced to *-oy- in most forms.
  2. A laryngeal in the sequence *VCHy was dropped. Examples: *wérye- ('say' present tense) from *werh₁- (cf. Homeric Greek eírei '[he] says', not *eréei); *h₂érye- ('plow' present tense) from *h₂erh₃- ('plow' cf. Lith. ãria '[he] plows', not *ária).
  3. A laryngeal in the sequence *CH.CC was dropped, where a syllable boundary follows the laryngeal (i.e. the following two consonants are capable of occurring at the start of a word, as in *tr- but not *rt-). An example is the weak stem *dʰugtr- given above, compared to the strong stem *dʰugh̥₂tér-.

It seems unlikely that this is a correct and complete description of the actual phonological rules underlying laryngeal deletion. These rules do not account for all the potential cases of laryngeal deletion (hence the many other rules that have been proposed); for example, the laryngeal in the desiderative suffixes *-h₁s- and *-h₁sy- appears to delete after an obstruent but not a resonant. In any case it is difficult to determine when a particular laryngeal loss is due to a protolanguage rule versus an instance of later analogy. In addition, as synchronic phonological rules the set of above rules is more complex than what is expected from a cross-linguistic standpoint, suggesting that some of the rules may have already been "morphologized" (incorporated into the morphology of certain constructions, such as the o-grade noun-forming rule or the rule forming y-presents); the above-mentioned laryngeal deletion in the desiderative suffixes may be an example of such morphologization.




  1. Tomic, O.M., Markedness in Synchrony and Diachrony, de Gruyter 1989, p. 99.
  2. See for example Ringe, D.A., On the Chronology of Sound Changes in Tocharian, AOS 1996, p. 152.
  3. Kümmel, M.J. (2007), Konsonantenwandel. Bausteine zu einer Typologie des Lautwandels und ihre Konsequenzen für die vergleichende Rekonstruktion. Wiesbaden: Reichert. Cited in Prescott, C., Pharyngealization and the three dorsal stop series of Proto-Indo-European.
  4. Meier-Brügger, Michael (2003). Indo-European Linguistics. p. 107. ISBN 3-11-017433-2.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  5. Simon, Zsolt (2013). "Once again on the Hieroglyphic Luwian sign *19 〈á〉". Indogermanische Forschungen. 118: 1–22.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  6. Beekes 1995:139
  7. Alexander Lubotsky. "Against a Proto-Indo-European phoneme *a" (PDF).<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  8. Mayrhofer 1986: 170 ff.
  9. 9.0 9.1 Fortson 2009:65
  10. Ringe 2009:9


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