What is Kōan?
A kōan (Japanese 公案; Chinese gōng'àn, public case) is a brief recorded exchange between a teacher and student, or an enigmatic statement, used in Rinzai Zen training as a question the discursive mind cannot answer. The student is given a case and holds it in zazen and in daily life until conceptual thought exhausts itself and a different register of response arises. This is the central contemplative practice of the Rinzai school of Zen, which developed in Tang-dynasty China and was restructured into its current graduated form in eighteenth-century Japan by Hakuin Ekaku.
Kōan vs shikantaza, aphorisms, and self-enquiry
A kōan is not a riddle. A riddle has a clever answer the riddler is withholding. A kōan has an answer the discursive mind is structurally incapable of producing. It is also not a kōan-style aphorism. The journey is the destination and what you seek is seeking you are the dorm-poster genre. They have nothing to do with the practice. There is no meaning of Mu that a careful reader extracts the way one extracts a parable's meaning. The cases were generated inside a face-to-face teaching relationship and presuppose one. The Sōtō tradition's shikantaza, just sitting without case or question, is in part an internal Zen critique of what kōan practice can become when its context is removed. Both schools sit. The argument over what is happening when they do is itself one of the longer-running cases in the literature. From a different lineage entirely, Ramana's self-enquiry holds a single question (Who am I?) against every conceptual answer until the question dissolves the questioner. The structural resemblance to kōan practice is real. The two traditions do not share a lineage.
The practice
What is the sound of one hand clapping? is the cliché example. What was your original face before your parents were born? is the older one. Mu, the syllable Zhaozhou gave in response to whether a dog has Buddha-nature, is the most worked over case in the Japanese curricula. The student is given a case and told to hold it during sitting and outside it, while walking, eating, and in private interview ([dokusan](lexicon:dokusan)) with the teacher. The discursive faculty is allowed to exhaust itself on the problem. What is supposed to emerge is not an answer but a different register of response. The lineage's own literature describes it, with characteristic Rinzai distrust of description, as direct seeing, the ground falling out, being met by the case.
The literary tradition
The kōan literature is the most extensive contemplative literature of any East Asian school. The two principal collections are the Wúménguān (Mumonkan or Gateless Gate, compiled in 1228 by the Chinese master Wumen Huikai) and the Bìyán Lù (Hekiganroku or Blue Cliff Record, compiled around 1125 from the verses of Xuedou). Both anthologise the recorded sayings of Tang and Song-dynasty teachers and surround each case with a poetic appreciation and a prose commentary. A third stratum, the Jǐngdé Chuándēng Lù (Transmission of the Lamp, 1004 CE), records the lineage genealogies in which the cases are embedded. It traces the transmission back through Bodhidharma to Mahākāśyapa's silent smile at the Buddha's flower sermon. Hakuin Ekaku restructured the curriculum into a graduated sequence in the eighteenth century. It begins with the breakthrough case, often Mu or the sound of one hand (the latter Hakuin's own composition), and continues through several hundred cases organised by what they were thought to test. This remains substantially the form taught in Rinzai monasteries today. The Sanbō Kyōdan school retained the Hakuin curriculum while loosening the monastic frame around it. It was the vehicle through which the practice reached many Western Zen teachers in the twentieth century.
Where to encounter it
The kōan curriculum is hard to receive without a teacher and a sustained training container. Its literature is mostly absorbed in the West through translations rather than through living transmission. The closest indirect approach in the existing entries is Adyashanti, who trained for fourteen years in the Maezumi-rōshi lineage descending from Hakuin through Sanbō Kyōdan. His teaching no longer uses formal kōan, but its rhetoric of short-circuiting the asking mind is recognisably the practice's residue. Rupert Spira's direct-path teaching is non-Buddhist in lineage but consonant in method. He treats the standing question what knows experience? as a permanently held question in the Rinzai sense.