Learn Polish: Szefa nie było w biurze. - The boss was not in the office.

This is a negative existential sentence, which is a grammatical way of saying we are stating that someone or something was not there. In Polish, when you say someone or something is absent, the logical subject (the boss) must take the genitive case (szefa).

Since szef is a masculine noun, why is the verb było (neuter) instead of był?

In these negative absence sentences, the verb acts impersonally. In the past tense, it locks into the third-person neuter singular form (było), no matter who or what is missing. Whether it is the boss (masculine), a woman (feminine), or multiple people (plural), the phrase will always be nie było.

Is it wrong to say Szef nie był w biurze?

Yes, for expressing absence, it is incorrect. Szef nie był... is typically used to describe what the boss wasn't (for example, Szef nie był miły - The boss wasn't nice). To say someone was physically absent from a location, Polish strictly uses the [Genitive subject] + nie było + [Location] structure.

Why does biuro (office) change to biurze here?