koan (kōˈän) [key] [Jap., = public question; Chin. kung-an ], a subject for meditation in Ch'an or Zen Buddhism, usually one of the sayings of a great Zen master of the past. In the formative period of Ch'an in China, masters tested the enlightenment of their students and of each other through statements and dialogue that expressed spiritual intuition in nonrational, paradoxical language. In later generations records of such conversations began to be used for teaching, and the first collections of subjects, or koans, were made in the 11th cent. Koan practice was transmitted to Japan as part of Zen in the 13th cent., and it remains one of the main practices of the Rinzai sect. The most famous koan collections are the Wu-men-kuan (Jap. Mu-mon-kan ) or "Gateless Gate" and the Pi-yen-lu (Jap. Heki-gan-roku ) or "Blue Cliff Records." A well-known koan is: "What is the sound of one hand clapping?"
See D. T. Suzuki, Zen Buddhism (1956); I. Miura and R. F. Sasaki, Zen Dust (1966); H. Dumoulin, A History of Zen Buddhism (1989).