
Sun Lu Tang
The study of WuJi in Xing Yi (excerpt from Xing Quan Xue: The Study of Form-Mind Boxing) p. 68
Sun Lu Tang is considered by many to be one of the primary sources for the basis and practice of the so-called Internal Boxing Arts such as Tai Chi Chuan, Xing Yi and Bagua Zhang. Besides being a key figure in their development he created his own version of each of these arts and wrote extensively on the theory. Many people have poured over the unusual mix of philosophical terms along with solid technical steps that play like a literary Yin and Yang of its own.
It is a difficult notation, and even top-notch Chinese instructors with good educations have told me that they find some of his writing abstract and unclear. Yet Sun persists, possibly because there is insight here along with experience, and possibly the poetic approach wins sometimes when the prosaic approach sputters out. Anyway, here is an excerpt, picked because it relates to the popular WuJi Breathing Exercises, well known among martial artists. Appended to the sample is what I hope will offer at least one version, a trial explanation I sincerely hope brings your participation, even on the personal level.

Sun Lu Tang
“Before training, there is no thought or intention, no figure or image, no self or others, only Qi exists in the chaos of the body. The state is called WuJi in Xing Yi. Without knowing the principle of “inverse motion,” people always rigidly adhered to the principle of the “direct motion nature.” Hence the internal Qi is restrained and things cannot be properly realized due to an obscure mind that causes the body to be weak. They do not know the principle of health that extreme Yang leads to Yin and extreme Yin leads to death. However, sages can be versed in the way of inverse motion, and control the relation between Yin and Yang, manage the principal of creation, direct Liang Yi (another name for Yin and Yang), grasp the key points, and go back to the pre-natal from the post-natal realm to settle at the original position as the body becomes an integral unit. Its way is nothing more than the principle of stretching and contracting as in post-natal Wu Xing and Bagua boxing. This is called the generation of Qi from WuJi.”
Interpretation:
People make much of the Pre-Natal and the Post-Natal aspects of these arts. To really feel the pre-natal you must enter into the spirit of the thing, banishing everything. Is this hard to do? It happens all the time, even in friendly sparring. But the martial practitioner should summon this up before practicing, it is a preparatory set insuring continual consciousness. When you are clear then Yin and Yang become clear, and you can control them like the two handles of a bicycle. These will always act in accord like respiration itself, and is therefore called generating Qi from Nothingness.