Q: Roshi, what is the difference between satori and kensho? I sometimes hear them spoken of as if they are the same. Why the different words for the same thing?
A: Satori is shedding body and mind in an instant, so that you experience the boundlessness of your "true-I"; kensho is clearly recognizing your "original face" and knowing it with absolute certainty, like someone who drinks water and knows if it is hot or cold. Huang-Po called kensho the "sudden mysterious tacit understanding." Satori is mainly an experience; kensho is mainly an illuminating understanding. They are not-two. But that doesn't mean they are the "same," as some dull-headed people might think.
Sometimes satori and kensho happen together, and sometimes not. A person may experience satori but not kensho, and in Chan such a person is said to be in danger of falling into a state of "one sided emptiness." They may even experience "Zen sickness" and start acting in wild and eccentric ways.
There are also some people who attain kensho (ken = seeing, sho = true nature) without experiencing satori. In that case, there is no sudden "dropping body and mind," just a clear and steady insight into where body and mind come from, like a lamp blazing deep in the night, or a giant pine tree leaning sideways in snow and fog.
Sixth Patriarch Hui-Neng had a satori when he heard a passing monk recite a verse from the Diamond Sutra, and the famous poem he wrote later on expresses this state, which might be called a living state of nothingness or voidness. But he had kensho only when his Master Hongren explained to him the meaning of that same Diamond Sutra verse late one night.
After his satori, Hui-Neng was inspired to go and find a teacher, because he knew there was still more to realize. He did that. He found Master Hongren. But after his kensho, wide-eyed in amazement, he merely cried, "Who would have thought that the mind itself is pure and clean, yet gives rise to everything in the universe?" He didn't need any teacher now. The Mind is the true Roshi.
In other words, Hui-Neng's kensho (thanks to Master Hongren's patient eyebrows) gave him a true understanding of what his satori had first opened up for him. That understanding was not "intellectual." It was just profound and real.
The nothingness of satori is extremely blissful and liberating, if you've spent a lot of time caught up in your thinking head, but it still isn't the ultimate. As Yuanwu says, breaking up "the habitual thinking consciousness" is still only going halfway, like falling in front of asses but behind horses.
The case of Elder Fu from the Blue Cliff Record illustrates this point grandly. Elder Fu was once stuck in a mountain monastery for three days and three nights during a big snowstorm. Given that he was the erudite type, the Abbot invited him to lecture on The Nirvana Sutra -- on which he was said to be an expert. During his lecture, the monastery's cook, who happened to be a Ch'an Buddhist, burst out laughing loudly. Elder Fu was startled, and asked what was wrong with what he'd said. The Ch'an cook told him that there was nothing wrong with it -- it's just that he hadn't experienced for himself so much as a grain of what he was talking about. Elder Fu begged for instruction:
The [Chan] cook said, "Give up lecturing for ten days, and meditate correctly in a quiet room; collect your mind, gather your thoughts, give up various clingings to good and bad all at once, and investigate exhaustively on your own."Fu did just as he had said, from the first to the fifth watch of the night; when he heard the sounding of the drum, he suddenly attained enlightenment [satori] and immediately went to knock on the Ch'an man's door. The cook said, "Who's there?" Fu said, "Me." The cook scolded him, saying "I would have you transmit and maintain the Great Teaching, explaining it in the Buddha's stead --why are you laying in the street drunk on wine in the middle of the night?" [the Ch'an cook is saying that satori is not the ultimate point of Zen -- it's just the start] Fu said, "Hitherto in my lectures on the scriptures I have been twisting the nostrils of the father and mother who gave birth to me; from today on, I no longer dare to be like this." [Fu has just experienced kensho on hearing the Ch'an cook's words, and instantly announces that he is going to live out and deepen his satori by taking some responsibility for himself.]See that outstanding fellow! Did he merely go accept this radiant spirituality and fall in front of asses but behind horses? He had to have broken up his habitual active consciousness, so that there is nothing that can be apprehended, yet he has still only realized one half. [Satori, in which nothing can be apprehended, is still realizing only one half.] An Ancient said, "If you do not give rise to any thought of practice or study, within formless light you'll always be free." Just discern that which is always silent and still, do not acknowledge sound and form, just discern spiritual knowledge, do not acknowledge false imagination. This is why it was said, "Even if an iron wheel is turning on your head, with concentration and wisdom complete and clear, they are never lost." [Kensho = spiritual discernment, concentration and wisdom complete and clear that are never lost, whereas satori can be lost -- or at least, temporarily misplaced.] (Thomas Cleary's translation, my notes.)