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kʷetwóres rule

The so-called kʷetwóres rule of Proto-Indo-European (PIE) has been observed by earlier scholars, but has only since the 1980s attracted enough attention to be named, probably first by Helmut Rix in 1985. It is a sound law of PIE accent, stating that in a word of three syllables é-o-X the accent will be moved to the penultimate, e-ó-X. Examples include

  • kʷetwóres < kʷétwores "four" (Latin: quattuor)
  • singular accusatives,
    • of r-stems, swes-ór-m̥ < swés-or-m̥ "sister" acc. singular
    • of r-stems, ǵʰes-ór-m̥ < ǵʰés-or-m̥ "hand" acc. singular
    • of s-stems, h2ews-ós-m̥ < h2éws-os-m̥ "Ausos" (Vedic Sanskrit uṣā́sam)

The rule is fed by an assumed earlier sound law that changes è to ò after an accented syllable, i.e. kʷetwóres < kʷétwores < kʷétweres.

Rix invokes the rule in the 1998 preface to the Lexikon der indogermanischen Verben (p. 22) to explain why in the PIE perfect the root ó grade is accented, e.g. ǵe-ǵónh- / ǵé-ǵn̥h- < ǵé-ǵenh- / ǵé-ǵn̥h- "created/engendered".

The rule has been invoked by Mottausch to explain accented ó grades in PIE nominal ablaut.


  • G. Klingenschmitt Die Lateinische Nominalflexion (1992), p. 44.
  • M. Kümmel, Stativ und Passivaorist (1996), p. 9.
  • K.-H. Mottausch, Die idg. Nominalflexion und die o-Stufe HS 113 (2000).
  • K.-H. Mottausch, Die thematischen Nomina im Idg. HS 114 (2001).
  • H. Rix, sūdor and sīdus in: FS Knobloch (ed. Ölberg, 1985), p. 348
  • K. Stüber, Die primären s-Stämme (2002), p. 24f.