Jakubinskij's law governs the distribution of the mixed Ikavian–Ekavian reflexes of Common Slavic yat phoneme, occurring in the Middle Chakavian area.
In the Southern Chakavian Ikavian area,[1] yat */ě/ was reflected as /i/, and became merged with the reflexes of Common Slavic */y/ and */i/.
The effect of Jakubinskij's rule has been levelled out in paradigmatic alternations and derivational morphology, by the analogical influence of nominative form onto the oblique cases, infinitive on other verbal forms, word stem onto derivations etc.
For example, Common Slavic *město 'place, position' would yield N sg mesto, but L pl is mestih, not **mistih.
[2] In 2023, the webcomic Saturday Morning Breakfast Cereal poked fun at Jakubinskij's Law, implying a pronunciation pattern in a defunct dialect does not deserve a named scientific law.