The Sung dynasty master Hung-chih Cheng-chueh (1091-1157), the best-known advocate of silent illumination, studied with a master called K'u-mu ("Dry-wood"), whose body resembled a block of wood when he sat. Hung-chih describes "silent sitting" as follows: Your body sits silently; your mind is quiescent, unmoving. This is genuine effort in practice. Body and mind are at complete rest The mouth is so still that moss grows around it. Grass sprouts from the tongue. Do this without cease. cleansing the mind until it gains the clarity of an autumn pool and the brightness of the moon illuminating the evening sky... In this silent sitting, whatever realms may appear the mind remains very clear in all details, with everything in its own original place. The mind stays on one thought for ten thousand years, yet does not dwell on any forms, inside or outside.

Silent illumination differs from outer path zazen, which generates a samadhi that lacks wisdom. By itself samadhi is silent but not illuminating. In silent illumination the mind is not fixed in samadhi but dwells in a bright state of illumination, which the meditator continually works to maintain. Although there are no thoughts, the mind is still very clear and aware. If such a nonattached state of mind can be maintained throughout one's daily life, that is true Ch'an.