～かどうか

～かどうか embeds a yes/no question inside a larger sentence: “whether (or not) X”. The embedded clause takes the plain form, and the whole ～かどうか chunk then works like a noun, you can know it, ask it, check it, or forget it.

1. Embedding a yes/no question

Take the question (行く？ “Will I go?”), put it in the plain form, and add かどうか. The main verb that follows is typically one of knowing, deciding, or checking.

2. With nouns and na-adjectives

Nouns and na-adjectives attach directly to かどうか, the だ is dropped. Say 本当かどうか, not 本当だかどうか.

Note: かどうか is only for yes/no questions. If the embedded question contains a question word like 何, いつ, or だれ, use か alone: いつ行くか分からない (“I don't know when I'll go”).

How to form it

Plain form + かどうか (drop だ after nouns and na-adjectives)

• 行く（いく）= to go → 行くかどうか（いくかどうか）= whether (I) will go or not
• おいしい = tasty → おいしいかどうか = whether it is tasty or not
• 本当（ほんとう）= true → 本当かどうか（ほんとうかどうか）= whether it is true or not

Key idea

～かどうか wraps a yes/no question into a noun-like package you can drop into a bigger sentence. Plain form before it, no だ after nouns, and save it for questions that can be answered with yes or no.