Breakdown of Nauczyciel zna mojego brata.
znać
to know (someone or something)
brat
brother
mój
my
nauczyciel
teacher
Questions & Answers about Nauczyciel zna mojego brata.
Why do we say mojego brata instead of mój brat?
Mój brat is the basic dictionary form. Because he is the direct object of the verb zna (the person being known), the phrase changes to the accusative case. For masculine animate nouns (people and animals), we add -a to the noun (brat becomes brata) and change mój to mojego.
Nauczyciel is also a living person. Why doesn't it get an -a ending like brata?
Nauczyciel is the subject of the sentence—the person doing the action. The subject always stays in the basic dictionary form (nominative case). Only the receiver of the action (the direct object) changes to the accusative case.
Wait, don't the endings -ego and -a belong to the genitive case?
They look exactly the same, but here they are accusative! For masculine animate nouns (people and animals), the accusative and genitive cases share the exact same endings. You know it is accusative here because the verb znać (to know) takes a direct object.
If the teacher knew an inanimate object, like a phone, would the endings be the same?
No. If a masculine noun is inanimate (a non-living thing), its accusative form looks exactly like its basic dictionary form. For example, my phone is mój telefon, so the sentence would simply be: Nauczyciel zna mój telefon.