"One cannot know everything."
Translation:Нельзя всё знать.
Practically all the russian sites I go to tell me never to use 'не можно'; you use нельзя for both "impossible" and "not allowed to".
Моей сестре нельзя есть шоколад. = My sister can't eat chocolate (maybe she can't digest it). This refers to capability.
Здесь нельзя курить. = You can't smoke here. You technically can smoke here but are forbidden by law. This refers to permission.
Kind of like how 'nor' is the opposite of 'or' but you can never say 'not or'.
I wrote невозможно and it allowed it. In all of the sentences I've seen, можно is always paired with an real subject rather than an implied one, so "He may not" rather than "one may not".
Also when I see "cannot", to me "не можно" is more like "one may not know everything" and doesn't have the exact same connotation, whereas невозможноis "it is impossible to know everything", which is the intention of this phrase.
А обезьяна может? Ваше русское предложение не полностью эквивалентно английскому. Английское говорит о принципиальной невозможности знать всё, не важно кто субьект. В русском языке подобное утверждение передаётся путём отсутствия подлежащего. В английском же, в котором подлежащие не может отсутствовать, существует техническое подлежащие - one
Not really sure why you say that the verb знать "requires an object in the accuative case... While the default (in most languages with case conjugation) is to have subject=nominative, (direct) object=accusative and indirect object=dative, it's not a 100% rule. In Russian, a typical twist to this truth is that a "negative direct object" takes genitive (aka the "non-ownership" of the non-existent thingy overrides the default accusative....if that's a way to put it. (Sorry for the lack of better wording!)
У её кошку --> She has a cat, with кошка conjugated into accusative because it's the object in the sentence)
У её нет кошки --> She does NOT have a cat, where кошка is conjugated into genitive because it's the "negative/non-existing object" (there's probably a better wording/explanation of this!)
Says a man whose language can't distinguish between he and she :) I'm affraid you have wrong preassumptions how a foreign language should work. It's an indefinite subject here: English uses a technical word 'one' to build such a sentence, Russian omits the subject altogether. Please, consult a corresponding section in your grammar book for more details.
English sentences require a subject even when making impersonal declarations. So we often use "One cannot..." or "You are not allowed..."
But these are only needed in English, in Russian we omit the subject. So «нельзя ...» and «можно ...» are all that's needed.
(Also, your sentence has spelling errors, not sure if that is important).
No. You shouldn't translate it word-for-word; Russian and English are two different languages that have their own idioms and ways for saying things. You wouldn't translate 'У меня есть карандаш' as 'At me there is a pencil' but 'I have a pencil'. Similarly, the impersonal construction works very differently in Russian than English; English grammar, unlike Russian, REQUIRES the sentence to always have a subject: here it is 'one' or, more likely, the impersonal 'you'.