かどうか

かどうか means "whether or not". It turns a yes-or-no question into part of a bigger sentence. The verb or adjective before it is in the plain form, present or past, and a noun or な-adjective drops だ.

The main verb is usually one of knowing, checking, deciding or asking: わかる分かる, しる知る, かくにん確認する, しらべる調べる, きめる決める, きく聞く.

• × 元気だかどうか → 元気かどうか
• × 行きますかどうか → 行くかどうか

かどうか or か

A question with a question word in it – where, who, what – takes plain か, never かどうか.

• × どこに行くかどうか決めましたか → どこに行くか決めましたか

For a yes-or-no question, plain か also works in conversation – くる来るかわからない分からない – but かどうか is the usual form and spells out the "or not".

Two outcomes

Because かどうか names both outcomes, it suits sentences about worry and uncertainty, where either answer matters.