To say what somebody IS, Polish puts the noun into the instrumental: jestem nauczycielem, not jestem nauczyciel. Masculine nouns take -em, feminine nouns take -ą, and the same case follows zostać (to become) and the preposition z (with). A bare adjective is the exception: it stays in the nominative (jestem zmęczony).
Examples
- Mój brat jest inżynierem w dużej firmie.
- My brother is an engineer at a big company.
- Po studiach chcę zostać lekarką.
- After university I want to become a doctor.
- Ona była wtedy studentką prawa.
- She was a law student at the time.
- Idę do kina z przyjacielem.
- I am going to the cinema with a friend.
The mistake to avoid
Saying "jestem nauczyciel" with the nominative. After być the profession takes the instrumental: jestem nauczycielem. Only adjectives stay nominative: jestem zmęczony.
Where this fits in
Who you are, who you become (instrumental), Polish B1: Say what someone is and what they become. Polish puts a profession or identity noun after być and zostać into the instrumental case, and the same case follows z (with) and the place prepositions przed, nad and między.