Questions & Answers about Mój brat lubi nowego nauczyciela.
Why does the word for teacher end in -a here (nauczyciela)?
The basic dictionary word is nauczyciel. Because it is the direct object of the verb lubi (the person being liked), it needs to be in the accusative case. For masculine animate nouns (living people or animals), we add -a to the end.
Why is the adjective nowego instead of nowy?
Adjectives always copy the case and gender of the noun they describe. Because nauczyciela is masculine animate and in the accusative case, the basic adjective nowy (new) changes to match it by taking the -ego ending.
Brat (brother) is also a living person. Why doesn't it get an -a ending like nauczyciela?
Because mój brat is the subject of the sentence—he is the one doing the liking. The accusative case endings are only used for the direct object (the person receiving the action). The subject always stays in its basic dictionary form.
I remember learning lubię for "like". Why is it lubi here?
Lubię means "I like". In this sentence, the subject is mój brat (my brother), which is a "he". Therefore, we must use the "he/she/it" form of the verb, which is lubi.