Breakdown of Этот факт нельзя доказать, потому что нет документов.
этот
this [f: эта, n: это]
потому что
because
нет
there is no / is not present
документ
document
Questions & Answers about Этот факт нельзя доказать, потому что нет документов.
Why do we use the perfective verb доказать with нельзя in this sentence?
In Russian, нельзя followed by a perfective verb means that an action is physically or logically impossible to successfully complete. Because there are no documents, achieving the result of proving the fact is impossible.
What would the sentence mean if we used the imperfective verb доказывать instead?
Using нельзя with an imperfective verb means that an action is prohibited. If the sentence said Этот факт нельзя доказывать, it would mean "You must not prove this fact" or "It is forbidden to prove this fact."
Is Этот факт the subject of the sentence?
No, sentences with нельзя are impersonal and don't have a grammatical subject. Этот факт is actually the direct object of the verb доказать. It is in the accusative case, which looks identical to the nominative case because факт is an inanimate masculine noun. It is placed at the front of the sentence to emphasize exactly what cannot be proved.
Why is документов in the genitive plural form?
The word нет (meaning "there is no" or "there are no") always requires the noun whose absence is being stated to be in the genitive case. Since we are talking about multiple documents, документ takes the genitive plural ending -ов.