か否か|かいなか
Means "whether or not." It turns a yes/no question into an embedded clause, usually the object or topic of verbs of deciding, checking or questioning. It is a formal, written equivalent of かどうか.
Particles: often followed by を, が or は, or by a comma before the main clause (e.g. 事実か否かを検証する)
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Used mainly in formal writing, reports, news and official speech, typically with verbs such as 決める, 決定する, 検証する, 確認する and 問う. It carries the same meaning as かどうか but sounds more formal and literary. In casual conversation, かどうか is the natural choice.
Do not insert だ between a noun or な-adjective and か否か; say 事実か否か, not 事実だか否か.
Learners sometimes confuse か否か with や否や, which means "as soon as" and follows only verbs.
Note that か否か sounds stiff in everyday conversation, where かどうか is preferred.
- かどうかN4「かどうか」 means essentially the same as 「か否か」 and the two are interchangeable; however, 「かどうか」 is stylistically neutral and common in both speech and writing, so use it in everyday conversation. It attaches directly to nouns and な-adjectives, as in 「学生かどうか」.
- や否やN1「や否や」 merely looks similar in form but has a completely different meaning: it means 'as soon as ~', attaches only to the dictionary form of verbs, and the following clause is usually in the past tense. 「か否か」 means 'whether', and can attach to verbs, adjectives, and nouns, so the two cannot be interchanged.
- を問わずN2「を問わず」 means 'regardless of ~', indicating that something is not limited by that condition, and it basically attaches only to nouns. 「か否か」 means 'whether ~', marking the object of judgment or investigation, and can attach to verbs, adjectives, and nouns. Their meanings differ, so they cannot be interchanged.
- にもかかわらずN2「にもかかわらず」 is a contrastive conjunction meaning 'although ~, nevertheless ~', where the preceding item is an established fact. 「か否か」 means 'whether', with the preceding item being two possibilities yet to be judged. Both are formal/literary, but their meanings differ, so they cannot be interchanged.
- か〜かN5「か〜か」 can pair any two options, used to have someone choose or to form an indirect question, and is stylistically neutral; 「か否か」 only contrasts affirmation and negation and is formal/literary. 「行くか行かないか」 can be replaced with the more formal 「行くか否か」.
か否か means the same as かどうか but is more formal, and it expresses a yes/no alternative, whereas か〜か lists two different options and や否や means "as soon as." を問わず means "regardless of" and にもかかわらず means "despite," so neither embeds a whether-question.
