How can substantiality and insubstantiality be distinguished between left and right or between top and bottom parts of the body?
The muscles, the skeleton and the nerves are parts of the body system. When practicing the movements, the use of consciousness to sink and relax the body is most important. The centre of gravity is moved while preserving the uprightness of the central axis of the body. It is important to focus on steadiness, tranquillity, relaxation and rootedness. The movements propel the external movements in a continuous or uninterrupted fashion. Internal force is generated with turning movements. After a long time, the whole body is in balance. When left and right is distinguished, one is substantial and the other insubstantial along the pattern of “cross alignment”. For instance, together with the distinction between top and bottom parts of the body, when the left upper part of the body is substantial, the left lower part is insubstantial and similarly when the right upper part of the body is substantial, the right lower part is insubstantial. This pattern of cross alignment is used in shifts of the centre of gravity from one leg to the other. This is similar to the “cross-roads” of the nervous system. When moving Qi, therefore, one must separate substantial from insubstantial, move the step without moving the body or moving the body and not the hand. If in moving a step, the body also moves, then it is not separating substantial from insubstantial. If in moving the body, the hand also moves, then the shoulder and the hands are not relaxed. It is important to follow the principles of using consciousness to propel movement. The top and bottom, left and right portions of the body must be coordinated. A rounded grinding stone may move but the centre is not moving. All parts of the body become one system characterized by lightness and agility, roundness and smoothness, even respiration, alternate opening and closing like that of the sea where with movement from one part of the sea, all parts are also moved. The movements are guided by consciousness and are properly regulated like the regular movements of the waves in the sea.
Reference: Interview with Master Huang www.paulrenalltaiji.info
Links: Yin Yang