20

{-ず} and {-ぬ} are two alternatives to the negative form {-ない} / {-ません}. But I noticed that depending on the word, it's either {-ず} or {-ぬ} although it seems like some words can take both suffix. Some examples I have encountered:
-ず
知らず (lyric in song "touch" by Younha)
わからず (lyric in song "aisur...