At first, we have to grasp it’s main point. Thousands of different methods can be concluded as one method. We won’t start from thousands of methods . Even though Taijiquan forms can vary in one thousand ways, there is only one systematic rule of motion. Movement must originate and be directed by the Dan-Tian, the central core of the body.
The Dan-Tian, located at three fingers below the navel (the three fingers should be horizontal to the ground when you are standing), is roughly the core, the center of the the body. By using this location as the center, supported by all of the parts of the body, then we can create this central core. For example, the center will move to other places in the body when we tilt backward with our hip joint. The center will be influenced when the shoulders become tight.
By relaxing the shoulders, sinking the elbows, letting the chest become concave, relaxing the waist, opening the groin, bending the knees, opening the crotch and emphasizing its becoming round, all of the above requirements are to let every part of the body support the Dan-Tian. This is to guarantee that the Dan-Tian is the center of the body, the core, and to clearly establish this center .The center will be influenced if there is only one deviated position in the whole body.
The central core of the Dan-Tian will be established when every part of the body is in an accurately aligned position. The Dan-Tian has the ability to connect the whole body together into a unified form. The relationship between the Dian-Tian and the body compensates for each other. When every part of the body is in the correct position, the center is formed. Then, the central core can drive the movement of the whole body.
Using the Dan-Tian as the core center of the body, if any part moves, the whole body moves together. This is whole body unified movement. Every joint connects to every other joint through the entire body. One joint by one joint connects the whole body with one Qi energy flow. This is the one systematic rule of motion.