I noticed that *Cj/*Cy (depending on if one uses IPA or IEist notation) and *Cw sequences are rare in PIE (with most being the result of schwebeablaut or regular ablaut). Among sequences that aren't the result of schwebeablaut or regular ablaut, *Tw sequences are the most abundant (with *T denoting any dental, including *s), followed by *Kw (*K denoting any dorsal), then by *Hw (*H denoting any laryngeal). The sequences with *j/*y are even rarer, with the same T>K>H pattern as sequences with *w. *C is never a labial or a resonant. Even the *Tw sequence represents a very tiny portion of reconstructed PIE. Any reason why C+glide sequences are rare and why the dentals are the most likely to be *C in both *Cj/*Cy and *Cw while *C is never a labial or resonant in such sequences?

Edit: there are also *Cj/*Cy and *Cw arising from combinations of different roots and elements. The above doesn't refer to clusters of such origin.

  • w and y are semivowels; I think I remember reading recently that a root *Cew- as a zero grade turns the labiovelar to a vowel, *Cu-. Imaginably the same holds for y>i. My lack of knowledge makes me wonder especially about Slavic with swoti ~ sloti on the one hand, and ljublu, sowjet etc, the [i] written as a reverse b of all things (< *lewbʰ- "love", Ger Lieb-).
    – vectory
    Commented Nov 7, 2019 at 3:33

1 Answer 1


The dearth of labial+w sequences is attested in many non-Indo European languages. The best explanation seems to be that it is a perceptually challenging sequence, where it is hardest to identify [pw] as being distinct from [p]. More specifically that is because labials and rounding both have a lowering effect on formants. The case of [kw] is in part because "kw" is analyzed as a single labio-velar phoneme, i.e. [kʷetwor], not [kwetwor]. A contrast between [kw] and [kʷ] would really hard to hear.

The [j] vs. [w] asymmetry in onsets is attested in a number of other families, for instance in Bantu onset cluster simplification tend to target [j] rather than [w]. The causes of this hasn't been studied systematically, but I have observed that it is often been that Cj clusters are targeted for some palatalization-like phenomenon, e.g. kj→tʃ, but merger of C+w into a single compromise place of articulation is not so common (nothing in Bantu like the IE kʷ→p/t pattern).

  • Needs an explanation for the absence of *Pj/*Py and resonant+glide sequences, the extraordinary rarity of laryngeal+glide clusters and why *Tj/*Ty is still more common than *Kj/*Ky (though it could have been due to the above mentioned palatalization, which if true could also apply to *Pj/*Py). Excellent job at explaining obstruent+/w/ sequences and providing examples from other language families though.
    – JMRD
    Commented Nov 6, 2019 at 1:08
  • the phonetics of *kʷ, like all other PIE phonemic symbols, are not solved. You say "would be hard to hear", what's the dependent clause? Personally, I memorize [kʷ] like French "quoi" or English "qu" with rounding, voice (and perhaps a backed tongue), while I can easily hold [kw] the German voiceless, way as in Quark, which is almost [kf] (there was a Ger.SE threat where different realizations of "qu" were observed). Even qof and how all those letters are written have a round big fat O. cp Ger Quartier vs AmE ca. "quorters" (quarters)
    – vectory
    Commented Nov 7, 2019 at 3:59
  • G'wehr as an apophone of Gewehr tends to voicelessness though. Uneconomic to be made heard, I'd say, . By the way, since I'm always keen to commit alternative facts, please compare *ghwer- "to burn" with the above.
    – vectory
    Commented Nov 7, 2019 at 4:08
  • PIE did, though rarely, contrast *ḱw and *kʷ (*eḱwos "horse").
    – TKR
    Commented Dec 6, 2019 at 20:10

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