Learn Croatian: Dobra večer, jeste li Vi liječnik? - Good evening, are you a doctor? formal

Capitalizing Vi is the standard way to show you are using the formal you to address one single person respectfully (like a stranger or a doctor). If you were talking to a group of people, you would just write a lowercase vi.

Why do we use jeste instead of the short form ste?

To ask a standard yes/no question, you use the question word li. However, the short forms of the verb to be (like ste) are lightweight words that cannot stand right before li. You must use the full, long form jeste to make jeste li.

If Vi uses a plural verb (jeste), why is liječnik in the singular form?

When using the formal Vi to address one person, the verb is always plural, but the nouns describing the person remain singular. This shows we are speaking to exactly one person formally, rather than an actual group of doctors.

How would this sentence change if I were speaking to a female doctor?

The formal Vi and the verb jeste stay exactly the same. However, you must change the noun to its feminine form to match the person you are talking to: Dobra večer, jeste li Vi liječnica?