Ivà ¡iÃÂ's law (), also Stang's law or StangâÂÂIvà ¡iÃÂ's law, is a Common Slavic accent law named after Stjepan Ivà ¡ià(1911) and Christian Schweigaard Stang (1957); the two linguists independently discovered the law in those years.
The law explains the origin of the Proto-Slavic neoacute accent occurring in the accent paradigm b as retractive from the following syllable.
During the Late Common Slavic period, the short vowels *àand *à(known as yers, also written *à*à Â) developed into "strong" and "weak" variants according to HavlÃÂk's law. The accented weak variants could no longer carry an accent, which was thus retracted onto the preceding syllable. That syllable gained a rising neoacute accent. It is denoted with a tilde diacritic â¨âÂÂÃÂâ© on historically "long" syllables (*a, *i, *u, *y, *ÃÂ, *ÃÂ, *ë, *VR) and with a grave accent â¨âÂÂÃÂâ© on historically "short" syllables (*e, *o, *ÃÂ, *ÃÂ).
In conservative Serbo-Croatian dialects of ÃÂakavian and Old à  tokavian (e.g., Slavonian), this neoacute is preserved as a separate tone, distinct from the old acute and circumflex. Ivà ¡iàdesignated the long neoacute in ÃÂakavian with the same circumflex symbol as the Lithuanian circumflex due to their phonetic similarity.
Compare:
PSl. *pirstuà> Common Slavic *pÃÂrstÃÂà> *pÃÂÃÂrstà(ÃÂakavian prÃÂst, Russian perst, N pl perstý)
Retraction also occurred on medial long circumflexed (i.e., non-acuted) syllables; for example, on verbs in *-iti. On the basis of the attested forms nÃÂsëte, vrãtite Ivà ¡iàassumed the earlier forms *nosÃÂte, *vortÃÂte, which would also yield the neoacute by retracting the long circumflex accent onto the preceding syllable. This retraction is uncontroversial if the preceding syllable is long; in the case of short preceding syllables, it is generally accepted, but some argue that it is analogical to the long neoacute in individual (mostly West Slavic) languages.
Additionally, Ivà ¡iÃÂ's law explains the acute accent on certain jÃÂ-stem nouns such as sà ©à ¡a (Slavonian à  tokavian dialects), vÃÂlja (with shortened neoacute).
Borrowings from other languages show that Ivà ¡iÃÂ's law operated after Dybo's law, and had the effect of partially reversing it. Compare: