The word koan, literally "public case", comes from the Japanese pronunciation of the Chinese characters (公案).
Koan-practice
Study of kōan literature is common to all schools of Zen, though with varying empahsises and curriculae.[12] A kōan or part of a kōan may serve as a point of concentration during meditation and other activities, often called "kōan practice" (as distinct from "kōan study", the study of kōan literature). Kōan may consist of a perplexing element or a concise but critical word or phrase (話頭 huàtóu) extracted from the story. It may also refer to poetry and commentary added to the story by later Zen teachers.
Instructions for kōan-practice
A qualified teacher provides instruction in kōan practice in private.
In the Wumenguan (Mumonkan), public case #1 ("Zhaozhou's Dog"), Wumen (Mumon) wrote:
...concentrate yourself into this 'Wú'... making your whole body one great inquiry. Day and night work intently at it. Do not attempt nihilistic or dualistic interpretations."[13]
Arousing this great inquiry or "Great Doubt" is an essential element of kōan practice. To illustrate the enormous concentration required in kōan meditation, Zen Master Wumen commented,
It is like swallowing a red-hot iron ball. You try to vomit it out, but you can't.
Japanese Rinzai
Kōan practice is particularly important among Japanese practitioners of the Rinzai sect. In Rinzai a gradual succession of koans is being studied.[19] There are two curricula being used within Rinzai, derived from the principal heirs of Rinzai: the Takuju curriculum, and the Inzan curriculum.
Koan practice starts with the shokan, or "first barrier", usually the mu-koan or the koan "What is the sound of one hand clapping?"[20] After having attained kensho, students continue their practice investigating subsequent koans.[21] In the Takuju-school, after breakthrough students work through the Gateless Gate (Mumonkan), the Blue Cliff Record (Hekigan-roku), the Entangling Vines (Shumon Kattoshu), and the Collection of Wings of the Blackbird (Chin'u shu).[22] The Inzan-school uses it's own internally generated list of koans.[22]
Hakuin used a fivefold classification system:[19] 1. Hosshin, dharma-body koans, are used to awaken the first insight into sunyata.[19] They reveal the dharmakaya, or Fundamental.[23] They introduce "the undifferentitated and the unconditional".[24]
2. Kikan, dynamic action koans, help to understand the phenomenal world as seen from the awakened point of view;[25] Where hosshin koans represent tai, substance, kikan koans represent yu, function.[26]
3. Gonsen, explication of word koans, aid to the understanding of the recorded sayings of the old masters.[27] They show how the Fundamental, though not depending on words, is nevertheless expressd in words, without getting stuck to words.[28]
4. Hachi Nanto, eight "difficult to pass" koans.[29] There are various explanations for this category, one being that these koans cut off clinging to the previous attainment. They create another Great Doubt, which shatters the self attained through satori. [30] It is uncertain which are exactly those eight koans.[31] Hori gives various sources, which altogether give ten hachi nanto koans:[32]
Miura and Sasaki:
Nansen’s Flower (Hekigan-roku Case 40)
A Buffalo Passes the Window (Mumonkan Case 38)
Sõzan’s Memorial Tower (Kattõ-shð Case 140)
Suigan’s Eyebrows (Hekigan-roku Case
Enkan’s Rhinoceros Fan (Hekigan-roku Case 91)
Shimano:
The Old Woman Burns the Hut (Kattõ-shð Case 162)
Asahina Sõgen:
Goso Hõen’s “Hakuun Said ‘Not Yet’” (Kattõ-shð Case 269)
Shuzan’s Main Cable (Kattõ-shð Case 280).
Akizuki:
Nansen Has Died (Kattõ-shð Case 282)
Kenpõ’s Three Illnesses (Kattõ-shð Case 17).
5. Goi jujukin koans, the Five Ranks of Tozan and the Ten Grave Precepts.[33][29]
According to Akizuki there was an older classification-system, inwhich the fifth category was Kojo, "Directed upwards". This category too was meant to rid the monk of any "stink of Zen".[34] The very advanced practitioner may also receive the Matsugo no rokan, "The last barrier, and Saigo no ikketsu, "The final confirmation".[34] "The last barrier" when one leaved the training hall, for example "Sum up all of the records of Rinzai in one word!"[34] It is not meant to be solved immediately, but to be carried around in order to keep practising.[34] "the final confirmation" may be another word for the same kind of koan.[34]
After completing the koan-training, Gogo no shugyo, post-satori training is necessary:[35]
[I]t would take 10 years to solve all the kôans [...] in the sôdô. After the student has solved all koans, he can leave the sôdô and live on his own, but he is still not considered a roshi. For this he has to complete another ten years of training, called "go-go-no-shugyô" in Japanese. Literally, this means "practice after satori/enlightenment", but Fukushima preferred the translation "special practice". Fukushima would explain that the student builds up a "religious personality" during this decade. I would say it is a kind of period that functions to test if the student is actually able to live in regular society and apply his koan understanding to daily life, after he has lived in an environment that can be quite surreal and detached from the lives of the rest of humanity. Usually, the student lives in small parish temple during this decade, not in a formal training monastery.[web 3]
Hakuin Ekaku recommended preparing for kōan practice by concentrating on qi breathing and its effect on the body's center of gravity, called the dantian or "hara" in Japanese — thereby associating kōan practice with pre-existing Taoist and Yogic chakra meditative practices.[citation needed]