by Master Li Ya-Hsuan (Student of Yang Cheng-Fu), in which he argues for the vertical lifting and sinking which produces the vertical circle and the true 3 dimensional circularity of movement.
太极立体圈, "太极理论真传" -- 太极拳大师李雅轩（杨澄甫弟子）论立体浮沉立体圈和真正的三向循环动法
"True Transmission of Taiji Principles" - Taiji Vertical Circle
1) 拳种之多，成百上千，实质上也不过是练习这些关节的不同的运动方法而已。 关节以灵活为贵，越是灵活，对我们的作用越大。
1. Although there are hundreds of styles of boxing, in fact they are all different ways of exercising according to a few key principles. Of the key principles, the most valuable is agility. The more agile, the better the boxing.
2. In the writings about Taijiquan, many authors emphasize that a boxing set must be performed from start to finish at a fixed height. Continuously performing a set at a fixed height forces the three large joints of the leg to operate in an extremely unnatural position, to the extent that it becomes impossible to develop the legs to their full potential. This kind of practice makes it easy for the leg to develop a kind of rigid strength, but it becomes impossible to develop natural elasticity. Therefore, when issuing energy, one can only push forward with the back leg. The resultant force is deliberate and unnatural, so the speed of movement will be slow and the result will seldom be satisfactory. This is the reason so many people practice so many years and are still unable to issue energy or the effect of the energy issued is poor.
3. Of those who advocate doing forms at a fixed height, most believe this is the only way to keep the center from floating up and of sinking the Qi to the Dantien in order to stabilize the body. What must be made clear is that the Qi sinking to the Dantien is a natural occurrence, and not the result of purposely forcing the air down. In regard to stability, this must be "stability in agility". Through relaxation of the whole body, the centre will naturally sink and the whole body will be stable. This "stability in agility" is not the same as forcing the center down. If one forces the center to sink in order to be stable, then the elasticity of the legs will be lost.
4. The theory of practicing a boxing set at a fixed height, without moving higher or lower, has no basis in the boxing classics.
5. Taijiquan is circular in form. This circularity is three dimensional. Seen from any angle, the movements are curves. If a set is performed at a fixed height, without moving higher or lower, then the movements of the waist and hip will be limited to two-dimensional (flat) movement.
6. The boxing classics say "as soon as one moves, every part of the body must be light and agile." If one performs a boxing set with contraction of the upper and lower body and elasticity is completely lost; then can one be light and agile? Besides this, it has been observed that performing sets at a fixed height with no variation has led to varying degrees of knee injuries. This is in opposition to the results of being naturally relaxed.
7. A boxing set should be performed with the head continuously floating up while the body continuously sinks. The first half of every posture lifts (during inhalation) while the second part sinks (during exhalation). Moreover, this sinking of the body comes about naturally due to the sinking of the Qi internally. During the sinking of the Qi, the opening or rounding of the "tang" (crotch area) causes the energy to sink to the soles of the feet. The soles of the feet will feel tightly compressed to the ground and the energy will be able to pass between the feet. The kung fu produced will be natural and relaxed and when issuing energy the legs will have tremendous power and speed and the force generated will be sudden and crisp. This force will be much greater than the force generated by pushing forward with the back leg.
8. Pushing forward with the back produces an indirect force and is deliberate and thus unnatural. This kind of force is out of harmony with principles of nature. On the other hand, the energy obtained by sinking is a direct force, produced by elasticity and rebound power. In addition, the energy produced by sinking can be issued instantaneously in response to intention.