Quote Originally Posted by Pyrius View Post
So, how would you know what Russian forms to use in context? Translating from Russian to English is easy. Going from English to Russian is a bit more challenging for me.
Does it help you that не always negates the constituent of the sentence which follows it? While in English you would say "you did not take the right key" with a certain ambiguity as to whether it was a failure to take a key or rather the wrong key, in Russian the negated element in "Вы взяли не свой ключ" must be свой. That means that in the Russian sentence the act of taking a key must have taken place, but it was "not yours", so it was by definition the wrong one. As you can see in all the examples, the negated element is always the one after не.