There's an academic field called historical linguistics, with a subfield called Slavistics. It's a solid scientific theory which is based on historical data and

There's an academic field called historical linguistics, with a subfield called Slavistics. It's a solid scientific theory which is based on historical data and typology. I may have gotten some details wrong, but it's generally how the sound changes occured according to mainstream academia. This page has some references at the bottom: https://en.m.wiktionary.org/wiki/Reconstruction:Proto-Slavic/%C5%A5u%C4%8F%D1%8C https://en.m.wiktionary.org/wiki/Reconstruction:Proto-Slavic...