Questions & Answers about Možemo ući u zgradu.
Why do we use ući here instead of the regular verb for going, ići?
ući is a perfective verb specifically meaning to enter. It is made by attaching the prefix u- (in or into) to the base of the verb ići (to go). We use ući because we are focusing on the completed action of crossing the threshold into the building.
Why do we say ući u? Isn't the concept of going into already included in the verb?
Even though the prefix u- on the verb ući already implies going into something, Croatian still requires you to use the separate preposition u right before the destination. This doubling up of a prefix and a matching preposition is a very common pattern with verbs of motion.
Why does the word for building change to zgradu instead of staying zgrada?
The preposition u triggers the accusative case here because it describes active motion toward a destination. For the feminine noun zgrada, the ending changes to -u. If we were already resting inside the building, we would use the locative case instead and say u zgradi.
Why doesn't ući change its ending to match the we form?
Because it directly follows the modal verb možemo (we can). Just like in English when you say we can enter, the second verb stays in its base dictionary form, which is called the infinitive.