Taijiquan is based on cultivating, unifying and controlling the life energy within the human body. This primal and vital energy is called Qi. When you move your muscles, you are using a bioelectric form of energy known as Yi. This is purely physical. But when you blend vital energy (Qi) with physical energy (Yi) and consciously control it with the mind, you develop a special kind of force or power called Jung(精) or Jing. It is this mind-body blend of Jing which powers the Thirteen Postures.
Five of these postures relate to the footwork of Tai Chi, which is responsible for moving the body smoothly and with stability, balance and “base.” These five stepping patterns – known as the Five Steps (五步) – include Step Forward, Step Backward, Turn Left, Turn Right, and Central Equilibrium. The remaining eight postures refer to how Jing is expressed in Tai Chi fighting techniques.
The Eight Energies are also known as the Eight Gates or Pal Mun (八門), these are connected back to the Tai Chi Compass. These eight are further divided into the four Primary energies, the four directions, and the four Secondary energies or four corners. The Primary energies are Ward Off, Roll Back, Press Forward and Push. The Secondary energies each blend two of the Primary energies to create Pull Down, Split, Elbow Stroke and Shoulder Stroke.