Learn Polish: Mój ojciec jest aktorem.

When you state someone's profession, identity, or nationality using the verb być (to be), Polish requires the noun to change its ending. This is called the Instrumental case. Because aktor is a masculine noun ending in a consonant, we add -em to the end, making it aktorem.

Why doesn't ojciec get an ending like aktorem does?

Ojciec (father) is the subject of the sentence—the person doing the action. The subject always stays in the basic dictionary form, known as the Nominative case. Only the profession part (aktorem) gets the special ending.

Since Polish doesn't have words for "a" or "an", how do we know it means "an actor"?

You're right, Polish doesn't use articles like "a", "an", or "the". The word aktorem simply means "actor", and you fill in the "an" or "the" in English based on what sounds natural. Here, "My father is an actor" is the only translation that makes sense.

If I wanted to point and say "This is an actor", would I still use aktorem?

Actually, no! If you use the pointing phrase to jest (this is / it is), you don't change the ending. You would just say To jest aktor. You only use the Instrumental ending (aktorem) when linking a specific person to their profession, like Mój ojciec jest aktorem (My father is an actor) or On jest aktorem (He is an actor).