There are three different levels of T’ai Chi Ch’uan—Heaven, Earth, and Human. The Human Level relaxes your sinews and vitalizes your blood; Earth Level “opens the gates” so that the ch’i can reach the joints; and Heaven Level exercises the sensory function. Each level has three degrees. The First Degree of the Human Level relaxes your tendons from the shoulders to the fingers. The Second Degree relaxes your tendons from the hip joint to the “bubbling well” [point in the bottom of each foot]. The Third Degree relaxes your tendons from the sacrum to the top of the head (ni wan). The Earth Level First Degree sinks the ch’i to the tan-t’ien. The Second Degree moves the ch’i into the bubbling well. The Third Degree circulates the ch’i so that it reaches the top of the head. The Heaven Level First Degree is t’ing chin. The Second Degree is tung chin. The Third Degree is omnipotence. These are the three levels and nine degrees.
(Cheng Tzu’s Thirteen Treatises on T’ai Chi Ch’uan, by Professor Cheng Man Ch’ing, translated by Benjamin Pang Jeng Lo and Martin Inn, pg 75, ©1985 by Juliana T. Cheng)
With regard to the statement that “the Human Level relaxes your sinews…”, it should be noted that sinews and tendons (like all fascia) stretch and resume shape, and cannot actually “relax”, per se. Although the mind cannot direct the stretch of fascia as it can the relaxation of muscles, it is possible to relax the muscles and permit the weight of the body to stretch the fascia associated with the muscles. In this manner, relaxation can cause fascial connections to stretch from the shoulder to the fingers, from the hips to the bottom of the feet, and from the sacrum to the top of the head.
The first level of the stage of earth “sinks the ch’i to the tan t’ien.” The tan t’ien is a point situated below and behind the navel, approximately 3/7ths of the way to the spine. Ch’i (literally “breath”) is here a synonym for the reciprocal activity effected through the occurrence of consciousness, and the activity focuses around the tan t’ien in the relaxed movement of breath because the tan t’ien is the pivot created by the two sides of the psoas muscle, as the sides of the psoas act in alternation over the pelvic basin.
Cheng offered a saying about the waist and the tan-t’ien from the historical literature of T’ai Chi, along with an explanation:
"The millstone turns but the axle does not turn". The turning of the millstone represents the turning of the waist. "The axle not turning" is equivalent to the equilibrium that comes from the sinking of the ch’i to the tan t’ien.
(Ibid, pg 90)
The waist turns, yet the reciprocal innervation of the psoas and extensor muscles that holds the body upright as the waist turns appears to pivot around the same location, the tan-t’ien. Cheng spoke of equilibrium because the narrow reciprocal activity in the vicinity of the tan-t’ien focuses the sense of three dimensions in consciousness as consciousness takes place, and the focus of the sense of three dimensions fosters reciprocal innervation around the waist appropriate to the support of the spine in the movement of breath.
Cheng spoke of an old Chinese description of self-cultivation, that he felt alluded to the fragile structure of the spine
Generally, ancient people referred to self-cultivation as cheng ching wei tso (straightening the clothes and sitting upright). The derivation of the word wei is difficult. Most people do not dare to interpret it as meaning ‘dangerous’. But I think the words wei tso contain the actual meaning of danger because the spine, like a string of pearls, has many sections ascending vertically.
(Ibid, pg 42)
The phrase “cheng ching wei tso” can perhaps also be translated as “straightening the clothes and sitting precariously”. “Straightening the clothes”, like “putting on the robe”, means generating feeling to the surface of the body; “sitting precariously” means sitting in such a manner as to witness the imbalance of the spine in the movement of breath and the consequent reciprocal activity generated in support of the spine.
Reciprocal activity to support the spine takes place in the extensor and psoas muscles, and in all the muscles that contribute to the motion of the body at the waist, including the muscles under and around the pelvis. The T’ai Chi classics say, “…the waist (is) the banner”; the breath generates motion from the tan-t’ien at the waist, much like a breeze generates motion from the line in a tethered flag.
Cheng explained how ch’i arrives at the “bubbling spring” in the bottom of the foot: first the ch’i (or reciprocal activity) is extended to the hips, he said, and then to the heels. Cheng says this process is referred to as “the true man breathing down to the heels”. Next the ch’i reaches the shoulders, elbows, and wrists, after which the ch’i can extend to the bottom of the foot and the middle of the palm.
As to how the ch’i reaches the top of the head, Cheng said that the ch’i moves through the sacrum, and in particular through the tail-bone, and that this effort cannot be forced. He advised the guidance of a teacher or fellow students.
Cheng’s caution is necessary because the reciprocal activity up the spine to the head-top in the extensors depends not only on fascial stretch behind the sacrum as the pelvis rotates on the hips, but also on the stretch of ligaments between the sacrum and the pelvis as the sacrum shifts in the cranial-sacral rhythm. Feeling for stretch between the sacrum and the pelvis develops with the free occurrence of consciousness, yet without feeling at the sacrum and throughout the body, the fluid support necessary to safely realize motion up the spine is lacking.
With regard to t’ing chin, Professor Cheng Man-ch’ing offered “listening to or feeling strength” as an explanation, but he also noted that the strength or “chin” referred to comes from the ligaments. For tung chin, Man-ch’ing translated “comprehension of chin” (comprehension of the strength from ligaments), and this comprehension, he said, occurred at different levels. Cheng’s explanation of t’ing chin and tung chin relied heavily on examples from the practice of T’ai Chi, yet the same principles apply in “straightening the clothes and sitting precariously” with the movement of breath: “as by day, so by night: as by night, so by day.”
Man-ch’ing’s explanation of “omnipotence” was in part as follows:
Wherever the eyes concentrate, the spirit reaches and the ch’i follows. The ch’i can mobilize the body, but you need not will the ch’i in order to move it. The spirit can carry the ch’i with it.
(Ibid, pg 80)
The activity of the stretch already in existence is ch’i, and the ch’i can mobilize the body from the balance associated with consciousness before any intention to act can be realized.
Cheng’s favorite examples of the power of T’ai Chi were stories of Yang family members, and what they did in their sleep or while half-awake. He told these stories to emphasize the connection between the occurrence of sense contact and the activity of ch’i, prior to the formation of intention.