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A kōan (公案?)//; Chinese: 公案; pinyin: gōng'àn; Korean: 공안 (kong'an); Vietnamese: công án) is a story, dialogue, question, or statement, which is used in Zen practice to provoke the "great doubt" and test a student's progress in Zen practice.
- 1 Etymology
- 2 Origins and development
- 3 Doctrinal background
- 4 Koan-practice
- 5 Varieties in koan-practice
- 6 Classical kōan collections
- 7 Examples of traditional kōans
- 8 See also
- 9 Notes
- 10 References
- 11 Sources
- 12 Further reading
- 13 External links
The Japanese term kōan is the Sino-Japanese reading of the Chinese word gong'an (Chinese: 公案; pinyin: gōng'àn; Wade–Giles: kung-an; literally: "public case"). The term is a compound word, consisting of the characters 公 "public; official; governmental; common; collective; fair; equitable" and 案 "table; desk; (law) case; record; file; plan; proposal."
According to the Yuan Dynasty Zen master Zhongfeng Mingben (中峰明本 1263–1323), gōng'àn originated as an abbreviation of gōngfǔ zhī àndú (公府之案牘, Japanese kōfu no antoku—literally the andu "official correspondence; documents; files" of a gongfu "government post"), which referred to a "public record" or the "case records of a public law court" in Tang-dynasty China.[note 1] Kōan/gong'an thus serves as a metaphor for principles of reality beyond the private opinion of one person, and a teacher may test the student's ability to recognize and understand that principle.
Commentaries in kōan collections bear some similarity to judicial decisions that cite and sometimes modify precedents. An article by T. Griffith Foulk claims
Gong'an was itself originally a metaphor—an article of furniture that came to denote legal precedents. For example, Di Gong'an (狄公案) is the original title of Celebrated Cases of Judge Dee, the famous Chinese detective novel based on a historical Tang dynasty judge. Similarly, Zen kōan collections are public records of the notable sayings and actions of Zen disciples and masters attempting to pass on their teachings.
Origins and development
Commenting on old cases
Gongans developed during the Tang dynasty (618–907) from the recorded sayings collections of Chán-masters, which quoted many stories of "a famous past Chán figure's encounter with disciples or other interlocutors and then offering his own comment on it". Those stories and the accompanying comments were used to educate students, and broaden their insight into the Buddhist teachings.
Those stories came to be known as gongan, "public cases". Such a story was only considered a gongan when it was commented upon by another Chán-master. This practice of commenting on the words and deeds of past masters confirmed the master's position as an awakened master in a lineage of awakened masters of the past.
Koan practice developed from a literary practice, styling snippets of encounter-dialogue into well-edited stories. It arose in interaction with "educated literati". There were dangers involved in such a literary approach, such as fixing specific meanings to the cases. Dahui Zonggao is even said to have burned the woodblocks of the Blue Cliff Record, for the hindrance it had become to study of Chán by his students Kōan literature was also influenced by the pre-Zen Chinese tradition of the "literary game"—a competition involving improvised poetry.
The style of writing of Zen texts has been influenced by "a variety of east Asian literary games":
- The extensive use of allusions, which create a feeling of disconnection with the main theme;
- Indirect references, such as titling a poem with one topic and composing a verse that seems on the surface to be totally unrelated;
- Inventive wordplay based on the fact that kanji (Chinese characters) are homophonic and convey multiple, often complementary or contradictory meanings;
- Linking the verses in a sustained string based on hidden points of connection or continuity, such as seasonal imagery or references to myths and legends.
Observing the phrase
During the Song dynasty (960–1297) the use of gongans took a decisive turn. Dahui Zonggao (1089–1163)[note 2] introduced the use of k'an-hua, "observing the phrase". In this practice students were to observe (k'an) or concentrate on a single word or phrase (hua-t'ou), such as the famous mu of the mu-koan.
In the eleventh century this practice had become common. A new literary genre developed from this tradition as well. Collections of such commented cases were compiled which consisted of the case itself, accompanied by verse or prose commentary.
Tahui's invention was aimed at balancing the insight developed by reflection on the teachings with developing samatha, calmness of mind. Ironically, this development became in effect silent illumination, a "[re-absorbing] of koan-study into the "silence" of meditation (ch'an)". It led to a rejection of Buddhist learning:
Some extent of Buddhist learning could easily have been recognized as a precondition for sudden awakening in Ch'an. Sung masters, however, tended to take the rejection literally and nondialectically. In effect, what they instituted was a form of Zen fundamentalism: the tradition came to be increasingly anti-intellectual in orientation and, in the process, reduced its complex heritage to simple formulae for which literal interpretations were thought adequate.
This development left Chinese Chán vulnerable to criticisms by neo-Confucianism, which developed after the Sung Dynasty. Its anti-intellectual rhetoric was no match for the intellectual discourse of the neo-Confucianists.
The recorded encounter dialogues, and the koan collections which derived from this genre, mark a shift from solitary practice to interaction between master and student:
The essence of enlightenment came to be identified with the interaction between masters and students. Whatever insight dhyana might bring, its verification was always interpersonal. In effect, enlightenment came to be understood not so much as an insight, but as a way of acting in the world with other people
This mutual enquiry of the meaning of the encounters of masters and students of the past gave students a role model:
One looked at the enlightened activities of one's lineal forebears in order to understand one's own identity [...] taking the role of the participants and engaging in their dialogues instead[note 3]
Kōan training requires a qualified teacher who has the ability to judge a disciple's depth of attainment. In the Rinzai Zen school, which uses kōans extensively, the teacher certification process includes an appraisal of proficiency in using that school's extensive kōan curriculum.
When the Chán-tradition was introduced in Japan Japanese monks had to master the Chinese language and specific expressions used in the koan-training. The desired "spontaneity" expressed by enlightened masters required a thorough study of Chinese language and poetry. Japanese Zen imitated the Chinese "syntax and stereotyped norms".
In the officially recognized monasteries belonging to the Gozan (Five Mountain System) the Chinese system was fully continued. Senior monks were supposed to compose Chinese verse in a complex style of matched counterpoints known as bien-li wen. It took a lot of literary and intellectual skills for a monk to succeed in this system.
The Rinka-monasteries, the provincial temples with less control of the state, laid less stress on the correct command of the Chinese cultural idiom. These monasteries developed "more accessible methods of koan instruction". It had three features:
- A standardized koan-curriculum;
- A standardized set of answers based on stereotypes Chinese sayings;
- A standardized method of secretly guiding students through the curriculum of koan and answers.
By standardizing the koan-curriculum every generation of students proceeded to the same series of koans. Students had to memorize a set number of stereotyped sayings, agyo, "appended words". The proper series of responses for each koan were taught by the master in private instruction-sessions to selected individual students who would inherit the dharma lineage.
Missanroku and missancho, "Records of secret instruction" have been preserved for various Rinzai-lineages. They contain both the koan-curricula and the standardized answers.[note 4] In Soto-Zen they are called monsan, an abbreviation of monto hissan, "secret instructions of the lineage". The monsan follow a standard question-and-answer format. A series of questions is given, to be asked by the master. The answers are also given by the master, to be memorized by the student.
Contemporary koan curricula
In the eighteenth century the Rinzai school became dominated by the legacy of Hakuin, who laid a strong emphasis on koan study as a means to gain kensho and develop insight. There are two curricula used in Rinzai, both derived from the principal heirs of Rinzai: the Takuju curriculum, and the Inzan curriculum. According to AMA Samy, "the koans and their standard answers are fixed."
Suppression in the Soto-school
During the late eighteenth and nineteenth century the tradition of koan-commentary became suppressed in the Soto-school, due to a reform movement that sought to standardise the procedures for dharma transmission. One reason for suppressing the koan-tradition in the Soto-school may have been to highlight the differences with the Rinzai-school, and create a clear identity. This movement also started to venerate Dogen as the founding teacher of the Soto-school. His teachings became the standard for the Soto-teachings, neglecting the fact that Dogen himself made extensive use of koan-commentary.
The popular western understanding sees kōan as referring to an unanswerable question or a meaningless statement. However, in Zen practice, a kōan is not meaningless, and not a riddle or a puzzle. Teachers do expect students to present an appropriate response when asked about a kōan. 
Koans are also understood as pointers to an unmediated "Pure Consciousness", devoid of cognitive activity. Victor Hori criticizes this understanding:
[A] pure consciousness without concepts, if there could be such a thing, would be a booming, buzzing confusion, a sensory field of flashes of light, unidentifiable sounds, ambiguous shapes, color patches without significance. This is not the consciousness of the enlightened Zen master.
[K]oan after koan explores the theme of nonduality. Hakuin's well-known koan, "Two hands clap and there is a sound, what is the sound of one hand?" is clearly about two and one. The koan asks, you know what duality is, now what is nonduality? In "What is your original face before your mother and father were born?" the phrase "father and mother" alludes to duality. This is obvious to someone versed in the Chinese tradition, where so much philosophical thought is presented in the imagery of paired opposites. The phrase "your original face" alludes to the original nonduality.
Comparable statements are: "Look at the flower and the flower also looks"; "Guest and host interchange".
Study of kōan literature is common to all schools of Zen, though with varying emphases and curriculae. The Rinzai-school uses extensive koan-curricula, checking questions, and jakogo ("capping phrases", quotations from Chinese poetry) in its use of koans. The Sanbo Kyodan, and its western derivates of Taizan Maezumi and the White Plum Asanga, also use koan-curricula, but have omitted the use of capping phrases. In Chinese Chán and Korean Seon, the emphasis is on Hua Tou, the study of one koan throughout one's lifetime. In Japanese Soto-Zen, the use of koans has been abandoned since the late eighteenth and nineteenth century.
Hua-tou or breakthrough-koan
In the Rinzai-school, the Sanbo Kyodan, and the White Plum Asanga, koan practice starts with the assignment of a hosshi or "break-through koan", usually the mu-koan or "the sound of one hand clapping". In Chinese Chán and Korean Seon, various koan can be used for the hua-tou practice.
Students are instructed to concentrate on the "word-head", like the phrase "mu". 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."
Arousing this great inquiry or "Great Doubt" is an essential element of kōan practice. It builds up "strong internal pressure (gidan), never stopping knocking from within at the door of [the] mind, demanding to be resolved". 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.
Analysing the koan for its literal meaning won't lead to insight, though understanding the context from which koans emerged can make them more intelligible. For example, when a monk asked Zhaozhou (Joshu) "does a dog have Buddha-nature or not?", the monk was referring to the understanding of the teachings on Buddha-nature, which were understood in the Chinese context of absolute and relative reality.[note 5]
The monk himself in his seeking is the koan. Realization of this is the insight; the response to the koan [...] Subject and object - this is two hands clapping. When the monk realizes that the koan is not merely an object of consciousness but is also he himself as the activity of seeking an answer to the koan, then subject and object are no longer separate and distinct [...] This is one hand clapping.
Various accounts can be found which describe this "becoming one" and the resulting breakthrough:
I was dead tired. That evening when I tried to settle down to sleep, the instant I laid my head on the pillow, I saw: "Ah, this outbreath is Mu!" Then: the in-breath too is Mu!" Next breath, too: Mu! Next breath: Mu, Mu! "Mu, a whole sequence of Mu! Croak, croak; meow, meow - these too are Mu! The bedding, the wall, the column, the sliding-door - these too are Mu! This, that and everything is Mu! Ha ha! Ha ha ha ha Ha! that roshi is a rascal! He's always tricking people with his 'Mu, Mu, Mu'!...[note 6]
But the use of the mu-koan has also been criticised. According to AMA Samy, the main aim is merely to "'become one' with the koan". Showing to have 'become one' with the first koan is enough to pass the first koan. According to Samy, this is not equal to prajna:
The one-pointed, non-intellectual concentration on the hua-t’ou (or Mu) is a pressure-cooker tactics, a reduction to a technique which can produce some psychic experiences. These methods and techniques are forced efforts which can even run on auto-pilot. They can produce experiences but not prajana wisdom. Some speak of ‘investigating’ the hua-t’ou, but it is rather a matter of concentration, which sometimes can provide insights, yet no more than that.
Testing insight - or learning responses
Sassho – Checking questions
Teachers may probe students about their kōan practice using sassho, "checking questions" to validate their satori (understanding) or kensho (seeing the nature). For the mu-koan and the clapping hand-koan there are twenty to a hundred checking questions, depending on the teaching lineage. The checking questions serve to deepen the insight of the student, but also to test his or her understanding.
Those checking questions, and their answers, are part of a standardised set of questions and answers. Students are learning a "ritual performance", learning how to behave and response in specific ways, learning "clever repartees, ritualized language and gestures and be submissive to the master’s diktat and arbitration."
Jakugo – Capping phrases
In the Rinzai-school, passing a koan and the checking questions has to be supplemented by jakugo, "capping phrases", citations of Chinese poetry to demonstrate the insight. Students can use collections of those citations, instead of composing poetry themselves.
After the initial insight further practice is necessary, to deepen the insight and learn to express it in daily life. In Chinese Chán and Korean Seon, this further practice consists of further pondering of the same Hua Tou.[web 1] In Rinzai-Zen, this further practice is undertaken by further koan-study, for which elaborate curriculae exist. In Soto-Zen, Shikantaza is the main practice for deepening insight.
Varieties in koan-practice
Chinese Chán and Korean Seon
In Chinese Chán and Korean Seon, the primary form of Koan-study is k'an-hua, "reflection on the koan", also called Hua Tou, "word head". In this practice, a fragment of the koan, such as "mu", or a "what is"-question is used by focusing on this fragment and repeating it over and over again:[web 2]
Who is it who now repeats the Buddha's name?
Who is dragging this corpse about?
What is this?
What is it?
What was the original face before my father and mother were born?
Who am I?[web 3]
This koan becomes a touchstone of our practice: it is a place to put our doubt, to cultivate great doubt, to allow the revelation of great faith, and to focus our great energy.
Kōan practice is particularly important among Japanese practitioners of the Rinzai sect.
Importance of koan-study
This importance is reflected in writings in the Rinzai-school on the koan-genre. Zhongfeng Mingben (中峰明本, Wade Giles:Chung-feng Ming-pen; Jpn. Chūhō Myōhon) (1263–1323), a Chinese Chán-master who lived at the beginning of the Yuan Dynasty, revitalized the Rinzai-tradition, and put a strong emphasis on the use of koans. He saw the kung-ans as "work of literature [that] should be used as objective, universal standards to test the insight of monks who aspired to be recognized as Ch'an masters":
The koans do not represent the private opinion of a single man, but rather the hundreds and thousands of bodhisattvas of the three realms and ten directions. This principle accords with the spiritual source, tallies with the mysterious meaning, destroys birth-and-death, and transcends the passions. It cannot be understood by logic; it cannot be transmitted in words; it cannot be explained in writing; it cannot be measured by reason. It is like the poisoned drum that kills all who hear it, or like a great fire that consumes all who come near it. What is called "the special transmission of the Vulture Peak" was the transmission of this; what is called the "direct pointing of Bodhidharma at Shao-lin-ssu" is this.
Musō Soseki (1275–1351), a Japanese contemporary of Zhongfeng Mingben, relativized the use of koans. The study of koans had become popular in Japan, due to the influence of Chinese masters such as Zhongfeng Mingben. Despite belonging to the Rinzai-school, Musō Soseki also made extensive use of richi (teaching), explaining the sutras, instead of kikan (koan). According to Musō Soseki, both are upaya, "skillful means" meant to educate students. Musō Soseki called both shōkogyu, "little jewels", tools to help the student to attain satori.[note 7]
In Rinzai a gradual succession of koans is studied. There are two general branches of curricula used within Rinzai, derived from the principal heirs of Rinzai: the Takuju curriculum, and the Inzan curriculum. However, there are a number of sub-branches of these, and additional variations of curriculum often exist between individual teaching lines which can reflect the recorded experiences of a particular lineage's members. Koan curricula are, in fact, subject to continued accretion and evolution over time, and thus are best considered living traditions of practice rather than set programs of study.
Koan practice starts with the shokan, or "first barrier", usually the mu-koan or the koan "What is the sound of one hand clapping?" After having attained kensho, students continue their practice investigating subsequent koans. 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). The Inzan-school uses its own internally generated list of koans.
Hakuin's descendants developed a fivefold classification system:
- Hosshin, dharma-body koans, are used to awaken the first insight into sunyata. They reveal the dharmakaya, or Fundamental. They introduce "the undifferentitated and the unconditional".
- Kikan, dynamic action koans, help to understand the phenomenal world as seen from the awakened point of view; Where hosshin koans represent tai, substance, kikan koans represent yu, function.
- Gonsen, explication of word koans, aid to the understanding of the recorded sayings of the old masters. They show how the Fundamental, though not depending on words, is nevertheless expressed in words, without getting stuck to words.
- Hachi Nanto, eight "difficult to pass" koans. 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. It is uncertain which are exactly those eight koans. Hori gives various sources, which altogether give ten hachi nanto koans:
- Miura and Sasaki:
- Nansen's Flower (Hekigan-roku Case 40)
- A Buffalo Passes the Window (Mumonkan Case 38)
- Sōzan's Memorial Tower (Kattō-shō Case 140)
- Suigan's Eyebrows (Hekigan-roku Case 8)
- Enkan's Rhinoceros Fan (Hekigan-roku Case 91)
- The Old Woman Burns the Hut (Kattō-shō Case 162)
- Asahina Sōgen:
- Goso Hōen's "Hakuun Said 'Not Yet'" (Kattō-shō Case 269)
- Shuzan's Main Cable (Kattō-shō Case 280).
- Nansen Has Died (Kattō-shō Case 282)
- Kenpō’s Three Illnesses (Kattō-shō Case 17).
- Miura and Sasaki:
- Goi jujukin koans, the Five Ranks of Tozan and the Ten Grave Precepts.
According to Akizuki there was an older classification-system, in which the fifth category was Kojo, "Directed upwards". This category too was meant to rid the monk of any "stink of Zen". The very advanced practitioner may also receive the Matsugo no rokan, "The last barrier, and Saigo no ikketsu, "The final confirmation". "The last barrier" when one left the training hall, for example "Sum up all of the records of Rinzai in one word!" It is not meant to be solved immediately, but to be carried around in order to keep practising. "the final confirmation" may be another word for the same kind of koan.
Completing the koan-curriculum in the Rinzai-schools traditionally also led to a mastery of Chinese poetry and literary skills:
[D]isciples today are expected to spend a dozen or more years with a master to complete a full course of training in koan commentary. Only when a master is satisfied that a disciple can comment appropriately on a wide range of old cases will he recognize the latter as a dharma heir and give him formal "proof of transmission" (J. inka shomei). Thus, in reality, a lot more than satori is required for one to be recognized as a master (J. shike, roshi) in the Rinzai school of Zen at present. The accepted proof of satori is a set of literary and rhetorical skills that takes many years to acquire.
After completing the koan-training, Gogo no shugyo, post-satori training is necessary:
[I]t would take 10 years to solve all the kōans [...] in the sōdō. After the student has solved all koans, he can leave the sōdō 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-shugyō" 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. 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 4]
Hakuin Ekaku, the 17th century revitalizer of the Rinzai school, taught several practices which serve to correct physical and mental imbalances arising from, among other things, incorrect or excessive koan practice. The "soft-butter" method (nanso no ho) and "introspection method" (naikan no ho) involve cultivation of ki centered on the tanden (Chinese:dantian). These practices are described in Hakuin's works Orategama and Yasen Kanna, and are still taught in some Rinzai lineages today.
Though few Soto practitioners concentrate on kōans during meditation, the Soto sect has a strong historical connection with kōans, since many kōan collections were compiled by Soto priests.
During the 13th century, Dōgen, founder of the Soto sect in Japan, quoted 580 kōans in his teachings. He compiled some 300 kōans in the volumes known as the Greater Shōbōgenzō. Dōgen wrote of Genjokōan, which points out that everyday life experience is the fundamental kōan.
However, according to Michel Mohr,
Sanbo Kyodan and White Plum Asanga
The Sanbo Kyodan school and the White Plum Asanga, which originated with the Soto-priest Hakuun Yasutani, incorporates koan-study. The Sanbo kyodan places great emphasis on kensho, initial insight into one's true nature, as a start of real practice. It follows the so-called Harada-Yasutani koan-curriculum, which is derived from Hakuin's student Takuju. It is a shortened koan-curriculum, in which the socalled "capping phrases" are removed. The curriculum takes considerably less time to study than the Takuju-curriculum of Rinzai.
To attain kensho, most students are assigned the mu-koan. After breaking through, the student first studies twenty-two "in-house" koans, which are "unpublished and not for the general public", but are nevertheless published and commented upon.[web 5] There-after, the students goes through the Gateless Gate (Mumonkan), the Blue Cliff Record, the Book of Equanimity, and the Record of Transmitting the Light. The koan-curriculum is completed by the Five ranks of Tozan and the precepts.
Classical kōan collections
Kōans collectively form a substantial body of literature studied by Zen practitioners and scholars worldwide. Kōan collections commonly referenced in English include:
- The Blue Cliff Record (Chinese: Bìyán Lù; Japanese: Hekiganroku), 12th century;
- The Book of Equanimity (also known as the Book of Serenity; Chinese: Cōngróng Lù; Japanese: Shoyoroku), 12th century;
- The Gateless Gate (also known as The Gateless Barrier; Chinese: Wúménguān; Japanese: Mumonkan) collected during the 13th century).
In these and subsequent collections, a terse "main case" of a kōan often accompanies prefatory remarks, poems, proverbs and other phrases, and further commentary about prior emendations.
The Blue Cliff Record
The Book of Equanimity
The Book of Equanimity or Book of Serenity (Chinese: 從容録 Cóngróng lù; Japanese: 従容録 Shōyōroku) is a collection of 100 Kōans by Hongzhi Zhengjue (Chinese: 宏智正覺; Japanese: Wanshi Shōgaku) (1091–1157), compiled with commentaries by Wansong Xingxiu (1166–1246). The full title is The Record of the Temple of Equanimity With the Classic Odes of Venerable Tiantong Jue and the Responsive Commentary of Old Man Wansong 萬松老評唱天童覺和尚 頌古從容庵錄 (Wansong Laoren Pingchang Tiantong Jue Heshang Songgu Congrong An Lu) (Taisho Tripitaka Vol. 48, No. 2004)
The Gateless Gate
The Gateless Gate (Chinese: 無門關 Wumenguan; Japanese: Mumonkan) is a collection of 48 kōans and commentaries published in 1228 by Chinese monk Wumen (無門) (1183–1260). The title may be more accurately rendered as Gateless Barrier or Gateless Checkpoint).
Five kōans in the collection derive from the sayings and doings of Zhaozhou Congshen, (transliterated as Chao-chou in Wade-Giles and pronounced Jōshū in Japanese).
The True Dharma Eye
Other kōan collections compiled and annotated by Soto priests include:
- The Iron Flute (Japanese: Tetteki Tosui, compiled by Genro in 1783)
- Verses and Commentaries on One Hundred Old Cases of Tenchian (Japanese: Tenchian hyakusoku hyoju, compiled by Tetsumon in 1771.)
Examples of traditional kōans
Does a dog have Buddha-nature
("Zhaozhou" is rendered as "Chao-chou" in Wade-Giles, and pronounced "Joshu" in Japanese. "Wu" appears as "mu" in Japanese, meaning "no", "not", "nonbeing", or "without" in English. This is a fragment of Case #1 of the Wúménguān. However, another koan presents a longer version, in which Zhaozhou answered "yes" in response to the same question asked by a different monk: see Case #18 of the Book of Serenity.)
The sound of one hand
Two hands clap and there is a sound. What is the sound of one hand? (隻手声あり、その声を聞け)
Victor Hori comments:
...in the beginning a monk first thinks a kōan is an inert object upon which to focus attention; after a long period of consecutive repetition, one realizes that the kōan is also a dynamic activity, the very activity of seeking an answer to the kōan. The kōan is both the object being sought and the relentless seeking itself. In a kōan, the self sees the self not directly but under the guise of the kōan ... When one realizes ("makes real") this identity, then two hands have become one. The practitioner becomes the kōan that he or she is trying to understand. That is the sound of one hand.[web 6]
Killing the Buddha
Thinking about the Buddha as an entity or deity is delusion, not awakening. One must destroy the preconception of the Buddha as separate and external before one can become internally as their own Buddha. Zen master Shunryu Suzuki wrote in Zen Mind, Beginner's Mind during an introduction to Zazen,
Kill the Buddha if the Buddha exists somewhere else. Kill the Buddha, because you should resume your own Buddha nature.
One is only able to see a Buddha as he exists in separation from Buddha, the mind of the practitioner is thus still holding onto apparent duality.
- A student asked Master Yun-Men (A.D. 949) "Not even a thought has arisen; is there still a sin or not?" Master replied, "Mount Sumeru!"
- A monk asked Dongshan Shouchu, "What is Buddha?" Dongshan said, "Three pounds of flax." (This is a fragment of case #18 of the Wumenguan as well as case #12 of the Blue Cliff Record.)
- A monk asked Zhaozhou, "What is the meaning of the ancestral teacher's (i.e., Bodhidharma's) coming from the west?" Zhaozhou said, "The cypress tree in front of the hall." (This is a fragment of case #37 of the Wumenguan as well as case #47 of the Book of Serenity.)
- Hacker koans, humorous expressions of hacker culture
- Koans mentioning Subhuti, Tanzan, and Tetsugen
- List of koans by Yunmen Wenyan
- Original face
- Wild fox koan
- Assertions that the literal meaning of kung-an is the table, desk, or bench of a magistrate appear on page 18 of Foulk 2000. See also 
- 大慧宗杲; Wade-Giles: Ta-hui Tsung-kao; Japanese: Daie Sōkō
- This role-taking is described by the Swedish psychologist of religion Hjalmar Sundén, though McRae does not seem to be aware of this
- In 1916 Tominaga Shūho, using the pseudonym "Hau Hōō", published a critique of the Rinzai koan-system, "Gendai sōjizen no hyōron", which also contained a translation of a missanroku. The missanroku part has been translated by Yoel Hoffmann as "The Sound of the One Hand" (see ).
- The controversy over whether all beings have the potential for enlightenment is even older. Vigorous controversy still surrounds the matter of Buddha nature. See "Tao-sheng's Theory of Sudden Enlightenment", Whalen Lai, in Sudden and Gradual (subtitle) Approaches to Enlightenment in Chinese Thought, p. 173 and 191. The latter page documents how in 429 or thereabouts (more than 400 years before Zhaozhou), Tao-sheng was expelled from the Buddhist monastic community for defending the idea that incorrigible persons (icchantika) do indeed have Buddha-nature (fo-hsing).
- Maura O'Halloran also gives an account of herself becoming mu.
- The term shōkogyu comes from a Chinese poem in which a lady calls the attendant using the word hsiao-yu, Jap. shōkogyu, to warn her lover. The poem figures in an interaction between Wu-tzu Fa-yen (1024–1104) and his student Yüan-wu K'o-ch'in, the teacher of Dahui Zonggao. Yüan-wu was assigned the koan "The verbal and the nonverbal are like vines clinging to a tree". Yüan-wu gained satori with the phrase "She keeps calling out to [her maid] Hsiao-yü although there is nothing the matter. It is only because she knows T'an-lang [her lover] will hear her voice". The same koan was assigned to Dahui Zonggao.
- Sasaki 1965, p. 4-6.
- Foulk 2000, p. 21-22.
- McRae 2003, p. 172–173, note 16.
- Foulk 2000, p. 21–22.
- Schlütter 2008, p. 111.
- Schlütter 2008, p. 109.
- Schlütter 2008, p. 1109.
- McRae 2003, p. 131.
- Yampolski 2003a, p. 20.
- Hori 2003, p. Chapter 4.
- Heine 2008, p. 52.
- Griffith Foulk 2000, p. 22.
- Schlütter 2008, p. 110.
- Griffith Foulk 2000, p. 23.
- Wright 2000, p. 208.
- Wright 2000, p. 209.
- Wright 2000, p. 209–210.
- Wright 2000, p. 210–211.
- Kasulis 2003, p. 30.
- McRae 2003, p. 130.
- Lachs 2012.
- Griffith Foulk 2000, p. 25.
- Bodiford 2006, p. 92–93.
- Bodiford 2006, p. 93.
- Bodiford 2006, p. 94.
- Bodiford 2006, p. 96–97.
- Bodiford 2006, p. 97–98.
- Bodiford 2006, p. 98.
- Hoffmann 1975.
- Bodiford 1993, p. 264, note 29.
- Bodiford 2006, p. 102–106.
- Hori 2000.
- Samy, p. 4.
- Sasaki 1965, p. xi.
- Hagen 2000.
- Aitken 1991, p. xiii, 26, and 212.
- Loori 1994, p. p64.
- Hori 2000, p. 282.
- Hori 2000, p. 284.
- Hori 2000, p. 289-290.
- Hori 2000, p. 310 note 14.
- Hori 2000, p. 289.
- Ford 2006, p. 35-43.
- Hori 2006.
- Mohr 2000, p. 245.
- Shibayama 1974.
- Sekida 1985, p. 138–139.
- Shibayama 1974, p. Commentary on case #1.
- Swanson 1997.
- Hori 2005b, p. 132.
- Ford 2006, p. 38.
- Hori 2000, p. 287.
- Hori 2000, p. 288-289.
- Satomi & King 1993, p. 106.
- O'Halloran 2007, p. 78.
- Samy, p. 5.
- Hori 2006, p. 132–133.
- Hori 2006, p. 133.
- Stephenson 2005.
- Hori 1999.
- Hori 2003.
- Sekida 1996.
- Hori 2005b.
- Schlütter 2000, p. 168.
- Dumoulin 2005b, p. 155.
- Dumoulin 2005b.
- Mingben 2006, p. 13.
- Dumoulin 2005b, p. 164–165.
- Dumoulin 2005b, p. 165.
- Schlütter 2000, p. 186.
- Schlütter 2000, p. 198 note 96.
- Schlütter 2000, p. 197 note 94.
- Besserman & Steger 2011, p. 148.
- Yampolski 2005, p. 186.
- Ford 2006, p. 42.
- Hori 2005b, p. 136.
- Hori 2005b, p. 136–137.
- Besserman & Steger 2011, p. 148-149.
- Hori 2005b, p. 137.
- Besserman & Steger 2011, p. 149.
- Hori 2005b, p. 138.
- Hori 2005b, p. 135.
- Hori 2005b, p. 139.
- Hori 2003, p. 23.
- Hori 2003, p. 23-24.
- Besserman & Steger 2011, p. 151.
- Hori 2005b, p. 143.
- Griffith Foulk 2000, p. 42.
- Hori 2005b, p. 145.
- Bodiford 1993, p. 144.
- Sharf 1995c.
- Ford 2006, p. 42–43.
- MacInnes 2007.
- Sharf 1995c, p. 432.
- Nonduality Magazine (2010), Interview with Stuart Lachs
- Dharmanet, Huatou
- hsuyun.org, The Hua-Tou Practice
- Muho Noelke, Part 10: What does it take to become a full-fledged Sōtō-shu priest and is it really worth the whole deal?
- Ruben L. F. Habito (2007), Foreword to Flowing Bridge: The Miscellaneous Koans
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- Aitken, Robert Baker (1991). The Gateless Barrier: The Wu-Men Kuan (Mumonkan). New York: North Point Press/Farrar.
- Besserman, Perle; Steger, Manfred (2011). Zen Radicals, Rebels, and Reformers. Wisdom Publications.
- Bodiford, William M. (1993). Sōtō Zen in Medieval Japan. University of Hawaii Press.
- Bodiford, William M. (2006). Koan practice. In: "Sitting with Koans". Ed. John Daido Loori. Somerville, MA: Wisdom Publications.
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- Hagen, Steven (2000). Introduction. In: The Iron Flute. 100 Zen Kōans. Nyogen Senzaki and Ruth Stout McCandless (trans.).
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- Hoffmann, Yoel (1975). The Sound of the One Hand. Yoel Hoffmann (trans.). Basic Books. ISBN 978-0-465-08079-3.
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- Sasaki, Ruth Fuller (1965). Introduction. In: Isshu Miura and Ruth Fuller Sasaki (1965), "The Zen Kōan". Harvest/HBJ.
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- Schlütter, Morten (2008). How Zen became Zen. The Dispute over Enlightenment and the Formation of Chan Buddhism in Song-Dynasty China. Honolulu: University of Hawai'i Press. ISBN 978-0-8248-3508-8.
- Sekida, Katsuki (1985). Zen Training. Methods and Philosophy. New York, Tokyo: Weatherhill.
- Sekida (translator), Katsuki (1996). Two Zen Classics. Mumonkan, The Gateless Gate. Hekiganroku, The Blue Cliff Records. Translated with commentaries by Katsuki Sekida. New York / Tokyo: Weatherhill.
- Sharf, Robert H. (1995c). "Sanbokyodan. Zen and the Way of the New Religions" (PDF). Japanese Journal of Religious Studies (22/3-4).
- Shibayama (1974). The Gateless Barrier. Zen comments on the Mumonkan. Translated from Chinese and Japanese into English by Sumiko Kudo. Shambhala Publications.
- Stephenson, Barry (2005), "The Koan as Ritual Performance", Journal of the American Academy of Religion June 2005, Vol. 73, No. 2, pp. 475–496
- Swanson, Paul L. (1997). Why They Say Zen Is Not Buddhism. Recent Japanese Critiques of Buddha-Nature. In: Pruning the Bodhi Tree. The Storm over Critical Buddhism. Jamie Hubbard and Paul L. Swanson, eds. University of Hawaii Press.
- Wright, Dale S. (2000). Koan History. Transformative Language in Chinese Buddhist Thought. In: "The Koan. Texts and Contexts in Zen Buddhism". Steven Heine and Dale S. Wright, eds. Oxford: Oxford University Press.
- Yampolski, Philip (2003a). Chan. A Historical Sketch. In: Buddhist Spirituality. Later China, Korea, Japan and the Modern World; edited by Takeuchi Yoshinori. Delhi: Motilal Banarsidass.
- Yampolski, Philip (2005). Hakuin Ekaku and the Modern Koan System. In: John Daido Loori,Thomas Yuho Kirchner (eds), Sitting With Koans: Essential Writings on Zen Koan Introspection. Wisdom Publications.
- Loori, John Daido. Sitting with Koans: Essential Writings on the Zen Practice of Koan Study. Wisdom Publications, 2005. ISBN 978-0-86171-369-1
- Steven Heine, and Dale S. Wright, eds. The Kōan: Texts and Contexts in Zen Buddhism. Oxford and New York: Oxford University Press, 2000. ISBN 0-19-511749-2
- Hoffmann, Yoel.tr. The Sound of the One Hand. Basic Books, 1975. ISBN 978-0-465-08079-3 This book contains examples of how some Zen practitioners answer the koans "correctly". Originally published in Japan almost a century ago as a critique of fossilization of Zen, that is formalization of koan practice.
- Samy, AMA (n.d.), Koan, Hua-t’ou, and Kensho (PDF)
- Stephenson, Barry (2005), "The Koan as Ritual Performance", Journal of the American Academy of Religion June 2005, Vol. 73, No. 2, pp. 475–496