Questions & Answers about Mój syn ma tremę przed ważnym występem.
Why are the words ważnym występem in the Instrumental case?
The preposition przed means "before" when talking about time (and "in front of" for location). In both situations, it requires the following words to be in the Instrumental case to show a fixed point in time or space.
Why does the adjective ważnym end in -ym?
It has to match the masculine noun it describes (występem) in the Instrumental case. For masculine and neuter adjectives in this case, the standard ending is -ym.
Why does the noun występem end in -em rather than -iem?
The dictionary form is występ. Because it ends in a hard consonant (p), it takes the regular -em ending in the Instrumental case. You only use -iem if a masculine noun ends in k, g, or a soft consonant.
Why is it tremę instead of trema?
The word for "stage fright" is trema, which is a feminine noun. Here, it is the direct object of the verb ma (has), so it must change to the Accusative case. Feminine nouns ending in -a change their ending to -ę in the Accusative.