Illich-Svitych's law

Proto-Slavic neuter o-stems with fixed accent on a non-acute root (accent paradigm b) become masculine, retaining the accent paradigm. Compare:

• PIE *dʰwórom n > OCS dvorъ m
• PIE *médʰu n 'mead' > PSl. *medu m (OCS medъ)

This rule is important because it operated after the influx of Proto-Germanic/Gothic thematic neuters, which all became masculines in Proto-Slavic. Late Proto-Germanic (after the operation of Verner's law) had fixed accent on the first syllable. Compare:

• PSl. *xlěvъ m 'pigsty' (OCS хлѣвъ) < PGm. *hlaiwą n
• PSl. *xysъ or *xyzъ m 'house' (attested derivatives PSl. *xyša and *xyža) < PGm. *hūsą n
• PSl. *pъlkъ m 'folk, people' (OCS плъкъ) < PGm. *fulką n

Proto-Slavic masculine o-stems with fixed accent on a non-acute root (accent paradigm b) become mobile-accent (accent paradigm c). This change is also termed "Holzer's metatony", after linguist Georg Holzer who described it.^[1]

Older literature suggests that this was not a Common Slavic innovation, and that there are exceptions in some Croatian Čakavian dialects of Susak and Istria, which have retained the original accentuation. This has been recently disputed.^[2]