The purpose of this study is to illuminate the philosophical context of Tai Ji Quan (太極拳) by investigating the Yin and Yang thought of I-Ching that is manifested in Tai Ji Quan theories, placing focusing on "Theory of Tai Ji Quan (太極拳論)" by Wang Zongyue (王宗岳). In addition, this study is to clarify the fundamentals and principles of combining the Yin and Yang thought of directions and hexagrams (卦象) in the eight diagrams (八卦) and five elements (五行) of I-Ching with the Tai Ji Quan theories and thirteen postures (十三勢), based on "The Explanation of Tai Ji Quan (太極拳釋名)" by Wang Zongyue, and to establish guidelines from the fundamentals and principles. For these purposes, the study was conducted as follows: First, it explored how the thoughts of I-Ching were embodied in Tai Ji Quan theories, focusing on Wang Zongyue''s "The Explanation of Tai Ji Quan" Second, it investigated the thirteen postures described in "The Explanation of Tai Ji Quan" and clarified the fundamentals and principles of combining the Yin and Yang thought of directions and hexagrams in the eight diagrams and five elements of I-Ching with the thirteen postures of Tai Ji Quan.
Tai Ji Quan is a martial art that begins with training on the harmony of strength and flexibility (剛柔) and of movement and suspension (動靜) and reaches the Way (道) as it adopts the eight diagrams and five elements of I-Ching, centering on Taegeuk (太極, the Supreme Ultimate). The cultural basis of Tai Ji Quan can be found in the Yin and Yang thought of I-Ching, one of the key features of Chinese traditional culture. Wang Zongyue greatly influenced the development of the Tai Ji Quan theories. He authored the theories on the basis of Taegeuk and combined the theories of the eight diagrams and five elements to create the thirteen postures. Wang Zongyue''s "Theory of Tai Ji Quan" and "The Explanation of Tai Ji Quan" describe the Tai Ji Quan theories based on the Yin and Yang thought of I-Ching and explain the principles of creating the thirteen postures according to the eight diagrams and five elements of Yin and Yang. Therefore, in this study, how the Yin and Yang thought of I-Ching is embodied in Tai Ji Quan was explored, based on Wang Zongyue''s theories.
This study found that Wang Zongyue''s "Theory of Tai Ji Quan", which can be considered as an important theoretical book on Tai Ji Quan, takes the Yin and Yang thought of I-Ching as its philosophical foundation and the rationale for the theories referred to in "Theory of Tai Ji Quan" is discovered in "Copulative (繫辭傳)." In addition, the thirteen postures that form the basis of Tai Ji Quan were found to correspond to the hexagrams of the eight diagrams and to the directions of the five elements of I-Ching, and the Yin and Yang (陰陽) and deficiency and excess (虛實) that each of the hexagrams means was discovered to constitute the substance and applications of the Tai Ji Quan postures. The results of the study are explained in more detail as follows.
First, the first part of "Theory of Tai Ji Quan" tells about the substance and implications of Tai Ji Quan. In other words, Tai Ji Quan is a martial art based on the Yin and Yang thought of I-Ching, so the law of Yin and Yang can be found in Tai Ji Quan. As for the motions (身法) of Tai Ji Quan, “The spirit, or Shen, reaches the top of the head, and the Qi sinks to the Tan-Tien. Keep the central position (虛領頂勁, 氣沈丹田, 不偏不依)." And for the usage (用法) of Tai Ji Quan, "Do not show anything substantial or insubstantial to your opponent. When the opponent brings pressure on one''s left side, that side should be empty; this principle holds for the fight side also. When he pushes upward or downward against one, he should feel as if encountering nothingness. When he advances, let him experience the distance as increasing drastically. When he retreats, let the distance seem exasperatingly short (忽隱忽現, 左重?左?, 右重?又杳, 仰之?高, 俯之?深，?之?愈?，退之?愈促)." These motions and usage embody the laws of I-Ching including ''Yin waning and Yang waxing'' (陰陽相濟, 陰陽消長, 剛柔相推), ''to use softness to conquer strength'' (以柔克剛), and ''the balance of weakness and strength'' (虛實轉換) and ''to use stillness to control movement'' (以靜制動). There are three stages of training of Tai Ji Quan: learning the postures (招塾), enlightened about the power of the postures (?勁), and passing through both the spirits and the postures (神明). The important thing in the training is to identify Yin and Yang, and deficiency and excess, to set the center of the body right, and to move the four limbs swiftly to avoid the disease of double-weightedness (雙重). The postures result in Yin and Yang.
Second, the Yin and Yang thought is fused in the Tai Ji Quan theories as its philosophical foundation. The laws of Tai Ji Quan are based on the hexagrams (卦畵, 卦名, 卦位, 卦象) of the eight diagrams of I-Ching, interlocking (交錯) of the hexagrams and Yin and Yang (卦 and 卦), change in the position of lines (爻位), and the like, so ''Yin waning and Yang waxing (陰消陽長),'' ''Yang waning and Yin waxing (陽消陰長),'' ''interdependence between Yin and Yang (陰不離陽, 陽不離陰, 陰陽互存),'' and ''a good combination of Yin and Yang is called Tao (一陰一陽謂之道)’ were observed, and then the features and meanings of the movements were established and applied in the Tai Ji Quan theories. As the Yin and Yang theory penetrates the Tai Ji Quan postures, there occurs a division of movements (動 and 靜), hardness and softness (剛 and 柔), imagery and reality (虛 and 實), and open and close (開 and 合).
Last, the thirteen postures of Tai Ji Quan are the movements forming the basis of Tai Ji Quan and develop eight upper body movements and five footworks based on the theory of the eight diagrams and five elements of the Taeguk, Yin and Yang thought of I-Ching. The eight laws of the Tai Ji Quan''s thirteen postures are Peng, Lv, Ji, An, Cai, Lie, Zhou, and Kao and correspond to the hexagrams of the eight diagrams of I-Ching. It can be thought that the meanings of Yin and Yang, and deficiency and excess that the hexagrams have are embodied as the capabilities, conversion between Yin and Yang, and distinction between deficiency and excess that each of the body parts reveals.
To summarize the results, the philosophical foundation of Tai Ji Quan is in the Yin and Yang thought of I-Ching, and the rationale for the Tai Ji Quan theories is found in Copulative (繫辭傳) of I-Ching. In addition, the thirteen postures of Tai Ji Quan make up the eight upper body movements and five footworks based on the theory of the eight diagrams and five elements of the Taeguk, Yin and Yang thought of I-Ching. Understanding this philosophical foundation of Tai Ji Quan will serve as a guideline for standardizing and practicing the Tai Ji Quan''s postures.