kao + nominative for a role or capacity

You already use kao to compare: Visok je kao brat — he is as tall as his brother. The same little word also says in what capacity someone does something: what job they do, what function they have at a meeting, what role they appear in. English uses as for this: She works as a doctor. Serbian uses kao.

The good news: the noun after kao does not change into a new case. When it describes the subject of the sentence — the person who works, appears, speaks — it simply stays in the nominative, the dictionary form, and it agrees with that person: a woman works as a lekarka, several waiters work as konobari.

The pattern

Plural forms are the ordinary nominative plurals you know: konobar → konobari, posmatrač → posmatrači, član → članovi, spasilac → spasioci, sestra → sestre.

Do not reach for the instrumental or the accusative after kao. English speakers who have learned biti + instrumental sometimes write radi kao lekarom or radi kao lekara — both are wrong. After kao, a role describing the subject is just lekar, lekarka, lekari.

As a doctor, or like a doctor?

English has two words, as and like. Serbian has one: kao. The form of the noun is the same in both, so the context tells you which meaning is meant.

• Verbs like raditi, zaposliti se, nastupiti, učestvovati, pojaviti se + kao usually give a real role (as).
• Verbs like ponašati se, govoriti, zvučati, izgledati + kao usually give a comparison (like).
• biti + kao + a person is usually a comparison: Bio mi je kao otac — he was like a father to me.

A role noun does not have to match the person's gender when the role itself has no feminine form or is used generally: Ona je ovde kao gost — she is here as a guest. Where a feminine job title exists (lekarka, novinarka, direktorka, sekretarica), use it for a woman.