So, if they wear socks: "skarpety" (acc, pl), and if they don't: "skarpet" (gen, pl). And the nom sg is "skarpeta". Am I right?
Genitive plural. Which for nouns ending in -a (like skarpeta) usually has no ending.
Right, in Polish "dopełniacz". Often mistaken with accusative ("biernik"), because it have similar questions (genitive: "kogo? czego? [nie ma]" - who? what? [is absent], accusative "kogo? co? [widzę]" - who? what? [I see])
4d1n, Your explanation above is better than my text book. Can you expand this 'Kto? Co?' for the cases please.
Mianownik (Nominative): kto? co? (to jest)
Dopełniacz (Genitive): kogo? czego? (nie ma)
Celownik (Dative): komu? czemu? (przyglądam się)
Biernik (Accusative): kogo? co? (widzę)
Narzędnik (Instrumental): z kim? z czym? (rozmawiam)
Miejscownik (Locative): o kim? o czym? (mówię)
Wołacz (Vocative): o!
This is something I've wondered about for a while: this sentence could be translated as "the big boys are not wearing socks". The two English sentences have different meanings. How, in Polish, is that difference expressed?
There is no difference in sentence structure in Polish for this. The listener ascertains the meaning of the speaker from the context of the conversation. For example, in English, you wouldn't say "Right now, I don't wear socks." You'd say "Right now, I'm not wearing socks." In Polish the "right now" is the context that determines your meaning.
Almost. The fact that it's negative is not enough to 'cause' Genitive. It's because the affirmative sentence took Accusative, that the negation causes Genitive.
Other cases just stay the same when negated.
The large boys wear no socks
Care to explain the difference_
"large boys" usually implies the size of the boys. "Big boys" often refers to age primarily with size following secondarily. Big boys are usually like age 10-preteen. Little boys are ages 4-9 maybe?
"nosić" (to wear) takes Accusative, but when a verb that took Accusative gets negated, it takes Genitive instead. This is the only case which changes when negated, other ones just stay the same.
However, one user recently pointed to me that the Clothing section suddenly uses Genitive which wasn't exactly introduced before, and there's a "Negations" skill afterwards - so this sentence probably shouldn't be here. Removed.