Question 1

Why does the word "квас" end in "-у" here (квасу) instead of the usual genitive "-а"?

Accepted Answer

This is the partitive genitive, sometimes called the "second genitive." For certain uncountable mass nouns like квас, чай, or сахар, adding -у or -ю indicates a quantity or "some" of that thing. So квасу specifically means "some kvass." You will also see the standard genitive кваса, but the -у form is very common when talking about portions of food and drink.

Question 2

Why is the preposition placed in the middle of ни у кого?

Accepted Answer

When a negative pronoun like никто (nobody) is used with a preposition like у (from/by), Russian splits the negative pronoun. The negative particle ни comes first, then the preposition, and finally the declined pronoun. That is why it is ни у кого rather than "у никого". You will see this same sandwich pattern with other prepositions, such as ни с кем (with nobody).

Question 3

Is квасу in the genitive case because the verb is negated?

Accepted Answer

It is actually working on two levels here! First, the verb просить (to ask for) naturally takes the genitive case when asking for "some" of an uncountable substance, which is why we use the partitive -у ending. Second, even if he were asking for a countable object, negated verbs in Russian frequently force their objects into the genitive case anyway.

Question 4

Why do we need не before the verb if we already used ни у кого (from nobody)?

Accepted Answer

Russian strictly requires double negatives. Whenever you use a negative word like ни у кого (from nobody) or никогда (never), you must also place the negative particle не right before the verb. Literally, the sentence translates to "He from nobody did not ask for some kvass."

Он ни у кого не просил квасу.

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