The term "Tai Chi" first appeared in the "Book of Change" better known as "I Ching", in which it is said "Out of Tai Chi is born two elements; out of two elements are born the four phenomenas; out of the four phenomenas are form the eight trigrams." The term Tai Chi here refers to the originator of everything. Later in the Northern Song Dynasty, a new-Confucian philosopher by the name of Chow Ton Yee expanded this notion with the contribution from Taoism. He used the Tai Chi symbol to demonstrate the common elements in everything. What he did was make a circle to represent Wu Chi stage. Inside this Wu Chi circle, he drew a wave line in the middle separating two equal black and white components to represent yin and yang. The black component represented yin and the white component represented yang. Inside the white component was a black dot to show that yin existed in yang and inside the black component was a white dot to show that yang existed in yin. With this he established a duality principle to explain that yin and yang are the most basic of all things. When these two components intercourse, everything multiplied. Later, when this duality principle became popular, people used the term "Tai Chi" as Tai Chi symbol to represent the universe. Now, we can see that the term "Tai Chi" in the Book of Change does not have the same meaning as the term "Tai Chi" in the "Tai Chi" symbol. The first one refers to the originator of all things and the second one refers to the duality principle.

The relationship of Tai Chi and Tai Chi Chuan is based on philosophy and experiences. Tai Chi contributing the philosophical component and Tai Chi Chuan contributing the experiences component. The symbol demonstrates that when Tai Chi Chuan is in motion, it will divide into yin and yang. This is what Wong Tueh Yeh wrote, "Tai Chi came from Wu Chi, mother of yin and yang. When it is in motion, it separates into yin and yang. When it is still, Yin and yang combined." This duality principle is exhibited in Tai Chi Chuan as hard versus soft, motion versus stillness, empty versus fullness, open versus closed.

Although there are many family styles of Tai Chi Chuan today, their routines and techniques may be different, their theories and principles are the same. All came from the Tai Chi symbol. If there is a style that does not follow the philosophy represented by the Tai Chi symbol, it is not Tai Chi Chuan. Why it is this art called Tai Chi Chuan? We already know that Tai Chi Chuan came from Wu Chi, Wu Chi gave birth to two elements, two elements gave birth to four phenomenas, four phenomenas gave birth to pa-kua's octagon and then to everything.

As described above, the Tai Chi symbol is a pair of complementary and contradictory components existing within one circle. Tai Chi is one circle, the yang becoming yin and the yin becoming yang continuously. Whatever happens, it will happen inside this one circle. Therefore, the movement has to be circular.

From this circular movements, we can see that Tai Chi Chuan must obey the same principle. It must move slowly and continuously. That is why the Tai Chi Chuan Classic said that there should be no stop and rough spot. Therefore, if one who practices Tai Chi Chuan has a stop and go movements, it is not Tai Chi Chuan. This does not obey the yin and yang, the interchanging, circular motion demonstrated inside the Tai Chi symbol.

People ask how these circular movements can be applied as martial art. The primary reason for these slow and circular movements is to improve health and longevity. Slow, even and circular movements make the breathing even and efficient. Lao Tzu had pointed this characteristic out in his book "Tao Teh Ching" where he said that stop and go movement such as fa jing techniques can cause rapid breathing. From its name, we know that this art came from Taoism. For the even, slow, continuous and coordinated movement is ideal for even and slow breathing. Even if one sweats a lot during practice, the heart beat does not rise. The secondary reason for the circular movement is that it loosens and relaxes the body. This relaxation is good for the tendons, ligaments and blood circulation. Tai Chi Chuan is the movement of stretching the tendons and ligaments. There is a saying, "one would rather lose one inch of muscle, but not one millimeter of tendons and ligaments."

Chinese martial arts practitioners have long concentrated on the development of tendons and ligaments, instead of muscles. This is true not only in Tai Chi Chuan but in all Chinese martial arts whether internal or external. Therefore, each system has its own method of training. In Tai Chi Chuan, the method is to stretch the tendons and ligaments in the solo form. Therefore, each posture must be comfortable and relaxed. Only with the circular movement of Tai Chi Chuan can one maximize stretching the tendons and ligaments without exhausting oneself. The tendons and ligaments have an advantage over ordinary muscles. The horse has thin legs, but has well developed tendons; therefore, it can run fast. The same is true of the deer. The crane also has thin legs but its tendons and ligaments allow it to support the body for a long time. Therefore, the essence in martial art training is to train the tendons and ligaments for combat strength. The circular, even, continuous and coordinated movements in Tai Chi Chuan is to train tendons and ligaments.

Now, we see why Tai Chi Chuan is such a difficult art to understand. It benefits in health, harmonizes breathing and at the same time it supports the demands of martial art training. Besides all the reasons listed above, some people say that it is called Tai Chi Chuan only when one has applied push hands techniques. The fact is that many people practice push hands in different martial art systems, not Tai Chi Chuan. The only way to determine if one is practicing Tai Chi Chuan is to see if its characteristics are like the Tai Chi symbol: characteristics like circular motion, yin and yang and its interchangeability. If a routine does not follow the Tai Chi symbol, it is not Tai Chi Chuan.

From a martial art standpoint, Tai Chi Chuan's circular motion is obviously suitable for physical combat. A circle has an inner and an outer side. The hands' movements works on the outer side of the circle while the waist works on the inner side of the circle. Therefore, any movement involving the rotation of the waist seems slow, but it is actually fast and can respond more quickly. It is like the physical concept of centrifugal force, in which the center rotation has a very small force while the outer circle has much greater force. As the Tai Chi Chuan classics said, " If the opponent does not move, I do not move. If the opponent moves, I am already there."