Breakdown of Эту дверь нельзя открывать!
дверь
door
этот
this [f: эта, n: это]
открывать
to open (imperfective)
нельзя
one must not
Questions & Answers about Эту дверь нельзя открывать!
Why is the imperfective verb открывать used here instead of the perfective открыть?
This is a special rule for the word нельзя. When you use нельзя with an imperfective verb (like открывать), it means an action is forbidden or you must not do it. If you used the perfective verb (открыть), it would mean the action is physically impossible (e.g., "The door is stuck, it is impossible to open it").
Where is the word for "you" in this sentence?
There isn't one! Words like нельзя (forbidden), можно (allowed), and надо (necessary) create impersonal sentences. They do not use a normal subject like "I" or "you". Literally, this sentence means "It is forbidden to open this door," which applies to anyone in general.
Why is it Эту дверь instead of Эта дверь?
It is in the accusative case because it is the direct object of the action—it is the thing being opened. The feminine word эта changes to эту. The noun дверь ends in a soft sign (-ь); it is a feminine noun that happens to look exactly the same in both the nominative and accusative cases.
If Эту дверь is the object, why is it at the very beginning of the sentence?