何故なぜ Common Adverb English jmdict 1 adverb (fukushi) word usually written using kana alone why;how;for what reason あなたはなぜ働いているの。 How come you're still working?
何故ならなぜなら Common conjunction English jmdict 1 conjunction word usually written using kana alone because;the reason is;if you want to know why 聞いて驚くなよ!今日から俺はピアノを始めるんだ。なぜなら私は音楽の先生になりたいからだ! Brace yourselves! From today I'm learning the piano. Why? Because I want to become a music teacher!