In [Rinzai] Zen, it is through the practice of susokkan or the koan that alignment of the mind is attained. Susokkan, which literally means “counting-the-breath meditation,” is the most basic practice in Zen for mind-alignment. It is not a mere breathing exercise, as it is often regarded even by experienced Zen practitioners; rather, it is the primary means by which we gather the ki in the tanden, and it leads to a thorough cleansing of the very roots of the mind. Traditionally, susokkan is said to consist of six “wonderful gates”—that is, six aspects or stages. The first is called su (literally, “to count”), in which one counts as one observes the inhalations and exhalations; the second is zui (“to follow”), in which one comes into harmony with the breathing and simply follows its movement as it flows in and out; the third is shi (“to stop”), in which the mind is focused in a state of oneness; the fourth is kan (“to observe”), in which one sees clearly and directly into the true nature of all existence; the fifth is gen (“to return”), in which the all-seeing eyes attained at the kan stage are turned inward to see clearly within oneself; and the sixth is jo (“to purify”), in which one reaches the state where not so much as a speck remains.
In susokkan, the out-breath should be long and steady. One breath after the other, inhale and exhale with the entire body, keeping centered in your lower abdomen and taking care not to force the outbreath, as this would prevent the expansive, free respiration necessary to zazen. The full exhalation should last for ten to fifteen seconds (or, for beginners, for about eight seconds, with eight seconds for inhalation, so that there are about four complete breath cycles a minute). As you become accustomed to this type of breathing, the exhalations will grow longer, while the inhalations will remain about the same length.
As mentioned above, the first stage of susokkan is counting the breaths; the counting in and of itself is not essential, but in the beginning it helps focus the attention on the breathing process. Slowly and expansively become one with each number, breathing and counting in a relaxed, unhurried manner free of all tension. Generally, one counts in a series of from one to ten, but it is also possible to count from one to a hundred or from one to a thousand, or even just to recite “one” over and over again. Allow the exhalations to be full and complete, aiding the process with the two small, relaxed pushes described above—this will lead to a very comfortable breathing cycle.
Again, the respiration in susokkan must not be forced or artificially controlled, as this would simply constrict the breathing process. Do not count in an automatic manner, but with relaxed yet complete attention. You must apply yourself unceasingly and with single-minded sincerity to this careful counting, working with ever-fresh attention and creativity. Exhale from the lower abdomen in an open, relaxed manner until your belly feels totally empty and the in-breath begins spontaneously; if you are too hasty or hurried, your practice will become mechanical and your mind will remain restless and unable to deepen into a state of intense concentration. At the beginning, your trunk tends to pull backward and the movement of the abdomen feels unnatural; you become very self-conscious about how the process is going, and about whether you are “succeeding” or not. As your sitting ripens with constant practice, you will be able to remain with your breathing quite naturally, your body in perfect harmony with the rhythm of respiration.
Focus on each individual breath, one after another, centering your consciousness in your tanden and filling it with energy. Breathe each breath totally, then forget it and move on to the next. Superficial concentration is useless—you must feel that the respiration is piercing through the ground to the very ends of the universe. Let no gaps appear between your concentration on one breath and the next. Continue like this, one focused breath cutting off all thought of the one before, cutting and cutting and cutting until there is no room for random ideas, no room for concepts of self, no room for inner noise. Your body, the zendo, the entire universe are all contained in this total focus on the breath, in this utter singleness of mind. There remains nothing to hold on to, nothing to depend upon.
This condition is known as samadhi of susokkan, where only the breathing and the counting remain; one has become the breathing; the mind is occupied with nothing else. In this state of true emptiness you feel completely refreshed, full of energy, and taut, yet fresh and lucid. This is the state of the first “wonderful gate” of susokkan, that of su.
In this way, follow the coming in and going out of your breath from morning until night. Count and count and keep on counting the breaths whether you are doing zazen or not; count whether you are standing or sitting, whether you are asleep or awake. As you continue, the inhalations and exhalations become completely natural, and finally you enter a clear, open state of perfect unity between mind and respiration, where it is no longer necessary to count to help focus your attention. This stage, in which the awareness and the breathing are one, with no need for numbers, is that of zui, “following.”
Then, at a certain point, all awareness disappears. This is the stage of shi, “stopping.” When this will happen cannot be predicted—it must occur naturally; it cannot be produced or forced. Some time after this “stopping” takes place you come back once again to awareness. This is kan, “to see.” Again, you cannot deliberately generate this state, it must happen of itself. Following this is gen, where you forget yourself completely, and finally jo, a state of mind that is bright, clear, and transparent. In all six of these stages—the natural path to samadhi—it is vitally important that one not attempt to force things but simply allow the process to unfold on its own.
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This state must be deepened to the point that all connection with the outside world is cut off and nothing whatsoever touches or enters your awareness. This does not mean, however, that the senses are shut down. Externally, the correct way to cut off connections is to collect the mind into a single point and maintain this state of absolute attention and clear awareness. Internally, it is to avoid holding on to anything at all. Do not get caught by thoughts or fantasies—just let the breath flow in and out while staying with susokkan or your koan. Allow the images that arise to come and go as they will—like pictures passing on a screen—but keep your awareness focused on the breath, allowing nothing to linger in your mind, until you and your breath become one.
Breathing never stops—it is with you all the time. You need only remain attentive to its flow. Even if thoughts arise, even if stimuli press in from the outside, just push on without pause, allowing no breaks in your awareness. Put everything into the process and move relentlessly ahead. No matter what comes along, do not let it become an obstacle. If you lack the courage to advance in one continuous line, you should not begin in the first place. To do zazen and susokkan just because you think you ought to will never lead to a true understanding of the mind. If you want to touch the True Mind that connects each and every one of us, you must be willing to push beyond any problems that arise.
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https://still-breathing.net/zazen-instruction/