Tai Ji Quan is the internal martial art that was created by the legendary Daoist Immortal Zhang San Feng in Wudang Mountain (info here). When people think of Tai Ji they generally only think of the slow movement style of Tai Ji Quan. However Tai Ji Quan is only one part of the three-part Tai Ji System. The three parts are Wu Ji, Tai Ji, and Liang Yi (better known as Tai Yi). Although they are defined separately they are complementary and integral to each other in practice.
The first part of the Tai Ji System is the practice of Wu Ji, translated as 'ultimate emptiness'. Through practicing Wu Ji, one works to cultivate the three treasures: Qi (energy), Jing (essence) and Shen (spirit). This internal alchemy helps one to better understand and communicate with the nature of the body and mind. With practice, cultivation of Wu Ji can be used to improve the physical well being to approach a better longevity and a balanced mind.
More about Wu Ji and three treasures here..
The second part of the Tai Ji system involves the well known practice of Tai Ji Quan. However, the full cultivation of Tai Ji is deeper than the series of slow coordinated movements. Tai Ji is the balancing interaction between yin and yang. The movements of Tai Ji Quan become the personified version of this; soft concealing hard, weak overpowering strong, balance between the two opposites. By practicing Tai Ji Quan one can open the channels of the body and relax tensions both physical and emotional. Tai Ji is also a great benefit to becoming internally aware. The main benefit, though, from the training of Tai Ji Quan is that it is a low impact style that can be progressed in at any age. Even though the training of Tai Ji does not require the expense of massive amounts of energy it is a lifelong experience that requires determination and a strong vigilance, consolidating the very idea of its own practice.
The final part of the Tai Ji System is the practice of Liangyi, from here written as Tai Yi. Contrary to Tai Ji Quan, balancing yin and yang, Tai Yi is defined as the separation of yin and yang. For this idea, Tai Yi uses slow and fast, soft and strong together to turn the internal energy into external strength through movements called Fajin, or explosive power. When yin and yang are separated through these movements, it is called the Two Extremes. Hence the namesake of the style Liangyi, meaning 'Two Extremes.' Tai Yi is known for its emphasis on body technique and coordination and the awareness and understanding of internal control.
The three parts of the Tai Ji System are interdependant as well as complementary in practice. In complete, the practice of Wu Ji is used to strengthen the mind and body and acheive longevity, the practice of Tai Ji is used to balance yin and yang and build internal energy, and the practice of Tai Yi is used to separate yin and yang to transfer the internal energy into external power. The parts also carry similarites as the goal of the complete system is similar.
When all elements of the Tai Ji System are cultivated one can develop the potential to creating not only a stronger, softer, cleaner, healthier and more aware being, but one can also learn to train natural intention to become more in harmony in their existence.