ojcem

In a sentence

• Mój ojciec jest lekarzem.

  My father is a doctor.

  The word 'ojciec' is used in its nominative form here as the subject of the sentence.

• Rozmawiałem z moim ojcem o wakacjach.

  I talked to my father about the holidays.

  Here, 'ojcem' is in instrumental case, as it appears after the preposition 'z', indicating 'with whom'.

• Jestem dumny z mojego ojca.

  I am proud of my father.

  In this sentence, 'ojca' is in genitive case due to the phrase 'z mojego' which requires it to express possession.