A kōan (公案; Japanese: kōan, Chinese: gōng-àn, Korean: gong'an, Vietnamese: công án) is a story, dialogue, question, or statement in the history and lore of Chán (Zen) Buddhism, generally containing aspects that are inaccessible to rational understanding, yet may be accessible to intuition. A famous kōan is: "Two hands clap and there is a sound; what is the sound of one hand?" (oral tradition, attributed to Hakuin Ekaku, 1686-1769, considered a reviver of the kōan tradition in Japan).
Kōans originate in the sayings and doings of sages and legendary figures, usually those authorized to teach in a lineage that regards Bodhidharma (c. 5th-6th century) as its ancestor. Kōans are said to reflect the enlightened or awakened state of such persons, and sometimes said to confound the habit of discursive thought or shock the mind into awareness. Zen teachers often recite and comment on kōans, and some Zen practitioners concentrate on kōans during meditation. Teachers may probe such students about their kōan practice using "checking questions" to validate an experience of insight (kensho) or awakening. Responses by students have included actions or gestures, "capping phrases" (jakugo), and verses inspired by the kōan.
