Numbers and cases!
Hi! I don’t quite understand when to use мільйони and мільйонів? When I tap the word it says the first is nom. And the second is gen. But why are they in different cases if in “два мільйони» and “п‘ять мільйонів» they are used in the same structure?
For "два/три/чотири (also 32, 63, 1494 ... and etc)" you need use "мільйони"(plural, nom)
For the rest number you need use "мільйонів"(plural, gen)
The reason they're different cases is because they are preceded by a different numeral. The reason the different numerals cause the following noun to be a different case is that that's just Ukrainian grammar is, nothing you can do about it
Historically we used to have 3 grammatical numbers: singular, plural and dual. This dual number doesn't really exists now (only coloquially in some dialects), but is the reason for the different kind of grammatical agreement for 2,3 and 4
А можно источник. Есть сомнения, что это производная от двойственного числа. А так, 1, 2, 3, 4 были "особенными" уже в праиндоевропейском.
Numbers that end in 1 have the singular ending.
Numbers that end in 2, 3 and 4 have the regular plural ending (usually -и/-і/-а).
Numbers that end in 5, 6, 7, 8, 9, 0 and the teens have a different ending which is apparently genitive plural (often -ів or knocking the final vowel off, but occasionally there'll be an extra vowel added in, so I find it hard working out how to form these sometimes).
I'm afraid I can't give you an explanation because I have an awful grasp of cases so just try to learn the rules without the terminology, but I do find it really annoying that it rarely seems to get mentioned. Many apps/articles/books just seem focus on the singular and regular plural when they're taking about numbers and forming plurals, and it feels like we're just expected to automatically know about the rest. You'll get a careful explanation on how to form the plural, but no mention that the genitive plural even exists, never mind how you're meant to form that. I guess it might be viewed as more complex grammar so they don't think it's something to put in the basics... but you're just as likely to need to talk about 5 of something as you are 3 of something, so I wish they would be taught together.
I long for somewhere to give you examples like this so it's really clear there are 2 plurals you'll need to know:
мільйон / мільйони / мільйонів
машина / машини / машин
друг / друзі / друзів
білка / білки / білок