Learn Croatian: Svaki gost se mora pridržavati pravila. - Every guest must adhere to the rules.

The reflexive verb pridržavati se (to adhere to / to abide by) strictly requires its object to be in the genitive case. While English uses the preposition "to" (adhere to), Croatian establishes this relationship directly through the genitive.

Why is the reflexive pronoun se placed before mora rather than right next to its main verb pridržavati?

Because se is an enclitic (a short word without its own stress), it naturally gravitates to the second position in the sentence. Here, the entire noun phrase Svaki gost acts as the first position, so se tucks in right after it, separating the subject from the modal verb mora.

How can we tell if pravila means "the rule" (singular) or "the rules" (plural) here?

In written form, you actually cannot tell! The base word is pravilo (a neuter noun). For neuter nouns, both the genitive singular and the genitive plural take the form pravila. We rely on the context of the sentence, which strongly implies the plural "rules".

Why do we use the imperfective verb pridržavati se instead of a perfective equivalent?

Following rules is an ongoing, continuous state of behavior rather than a single, completed action. Because the guests must constantly maintain this behavior, the imperfective aspect is required.