In Rinzai Zen, koan practice is directed toward a direct, non-conceptual realization of one’s true nature, often referred to as kenshō or satori. The koan functions not as a riddle to be solved intellectually, but as a catalyst that undermines reliance on logical reasoning and fixed views. By confronting a question or anecdote that cannot be resolved through ordinary thought, the practitioner is gradually brought to the limits of discriminating intellect. This process aims at a radical shift in perception, in which reality is experienced immediately rather than filtered through conceptual frameworks.

A central aspect of this discipline is the deliberate exhaustion of the rational, dualistic mind. As the practitioner wrestles with the koan, habitual patterns of analysis and explanation are pushed to the breaking point, generating a state sometimes described as “great doubt.” In that crucible of doubt, where familiar mental strategies fail, the conditions are created for a sudden breakthrough beyond subject–object thinking. This breakthrough is not an abstract understanding, but a direct, experiential insight into Buddha-nature or emptiness, in which the ego-centered perspective falls away.

Koan practice also serves as an ongoing means of testing and refining this insight under the guidance of a teacher. The initial awakening is not treated as a final attainment, but as something that must be verified, deepened, and integrated into conduct. Through repeated encounters with different koans and continual “checking,” the practitioner learns to let the awakened perspective permeate ordinary activities. In this way, the koan becomes both the trigger for sudden realization and a continuing measure of how fully that realization is embodied in clear awareness and compassionate action.