か

The particle か is used to turn a statement into a question. At its most common, it appears at the end of a sentence to ask a yes/no question (for example, 今日は忙しいですか。“Are you busy today?”). It can follow verbs, adjectives, and nouns (例: 行くか、来るか, 本ですか, 忙しいですか). It is also used to express an internal question or doubt, and in spoken language it often invites confirmation or a guess about the speaker’s knowledge. In more complex sentences, か appears in embedded questions or in a choice structure like AかBか, meaning “whether A or B,” or “A or B.” Keep in mind that politeness affects form (です/ます styles) and intonation, but the basic function remains to mark a question or uncertainty.