Questions & Answers about Mój brat nie boi się węży, ale boi się pająków.
Why are węży and pająków in the Genitive case instead of the Accusative?
The verb bać się (to be afraid of) always requires the noun that follows it to be in the Genitive case. Even though they are the direct objects of the emotion, you must use the Genitive forms węży (snakes) and pająków (spiders).
Does the nie in nie boi się affect the case of the noun?
In Polish, negating a verb normally changes an Accusative object into a Genitive one. However, since bać się already takes the Genitive case by default, the negation doesn't actually change anything here. Both the negative nie boi się węży and the positive boi się pająków use the Genitive plural.
If both węży and pająków are Genitive plural masculine nouns, why do they have different endings?
The Genitive plural ending for masculine nouns depends on the last consonant of the word's base form. Pająk ends in a "hard" consonant (k), which usually takes the -ów ending. Wąż ends in a "historically soft" consonant (ż), which typically takes the -y or -i ending.
The dictionary word for snake is wąż. Why does it spell with an ę in węży?