Kōan: Zen Buddhist paradoxical prompt and teaching device

Kōans are often quite interpretable by rational methods. For some Kōans, the Zen student is expected to find the correct solution by reasoning. For most Kōans, all rational solutions to the Kōan are considered wrong. The actual meaning of these Kōans, their essential function, is only revealed intuitively, without words. There are various views on the meaning of Kōans within Rinzai Zen: While Daisetz Teitaro Suzuki, for example, invokes a contradictory-seeming Sokuhi logic, Ruth Fuller-Sasaki asserts the "fullness of meaning" of Kōans.

The goal of Kōan practice is the realization of non-duality. The illusion that things are different and that the ego has its own existence separate from the rest is to dissolve in the Kōan practice.

The Zen student is given a specific Kōan appropriate to his maturity (e.g., the Kōan Mu: A monk asked Joshu (Chinese Zhaozhou), "Does a dog have Buddha-nature or not?" Joshu replied, "Mu!"). This Kōan is to be presented by the person thus questioned to the master in personal conversation (dokusan) to show that he has grasped the true content of the Kōan during meditation. Novices and monks must master a series of Kōans. To determine whether they have actually succeeded, the student is instructed to find a key word (jakugo) appropriate for the corresponding Kōan. Depending on the temple affiliation, the order of the Kōans to be mastered, along with their corresponding jakugo, is fixed. Over the centuries, this "curriculum" has solidified. As an inner experience, this realization is not to be confused with an intellectual grasp of the problem. It is not an interpretation of the Kōan or an explanation. This happens occasionally in the Teishō. The student's individual insight would often seem even more meaningless to the layman than the Kōan itself. From the student's reaction to the Kōan, the experienced master can tell whether the student is making progress on the path of Zen, or whether he is persisting in illusion and error. The Zen master's written or oral comments on a Kōan are called Agyō (granted words).

This method of practice and examination is used primarily in the Rinzai direction of Zen.

There are five "classes" of Kōans that serve different functions.

1. Hosshin-Kōans (hosshin: Jap. for Dharmakaya, Trikaya), are Kōans that help the disciple break through to awakened vision and become at home in the world of the True Being, the Buddha-nature (Bussho). The Hosshin Kōans are about the world of "non-differentiation" (non-attachment, non-judgment), but the student must not stop at this level of experience.
2. The Kikan-Kōans (kikan: Jap. "aid, tool") are intended to train the student's capacity for discernment in non-attachment. Here the teaching of non-attachment and non-valuing is intensified.
3. The Gonsen-Kōans (gonsen: Jap. "clarification of words") is about the deepest meaning and content of the sayings and formulations of the old masters, beyond lexical definition and conceptual "representation". It goes beyond the conceptuality of etymology.
4. Finally, the Nanto-Kōans (nanto: Japanese for "difficult to pass") are those Kōans that are particularly difficult to solve.
5. Once the student has mastered the various Kōans of Grades 1 to 4, then with the Go-i, the Five Degrees (of Enlightenment), his True Comprehension is once again thoroughly examined and put to the test.

• Haiku
• Riddle
• Catch question, catch conclusion