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太虚者，太极也，太极本无极，故曰太虚。天元纪大论曰∶太虚廖廓，肇基化元。此之谓也。
太极者，天地万物之始也。太始天元册文曰∶太虚廖廓，肇基化元。老子曰∶无名天地
之始，有名天地之母。孔子曰∶易有太极，是生两仪。邵子曰∶若论先天一事无，后天方要
着工夫。由是观之，则太虚之初，廓然无象，自无而有，生化肇焉，化生于一，是名太极，太极动
静而阴阳分。故天地只此动静，动静便是阴阳，阴阳便是太极，此外更无余事。朱子曰∶太极分
开，只是两个阴阳，阴气流行则为阳，阳气凝聚
则为阴，消长进退，千变万化，做出天地间无限事来，以故无往而非阴阳，亦无往而非太极。
夫太极者，理而已矣。朱子曰∶象数未形理已具。又曰∶未有天地之先，毕竟先有此理。先
儒曰∶天下无理外之气，亦无气外之理。故理不可以离气，气不可以外理，理在气亦在，气
行理亦行。夫既有此气，则不能无清浊而两仪以判；既有清浊，则不能无老少而四象以分。
故清阳为天，浊阴为地，动静有机，阴阳有变。由此而五行分焉，气候行焉，神鬼灵焉，方隅
位焉。河洛布生成之定数，卦气存奇偶之化几。有死有生，造化之流行不息；有升有降，气
运之消长无端。体象有常者可知，变化无穷者莫测。因而大以成大，小以成小，大之而立
天地，小之而悉秋毫，浑然太极之理，无乎不在。所以万物之气皆天地，合之而为一天地；
天地之气即五物，散之而为万天地。故不知一，不足以知万；不知万，不足以言医。理气阴
阳之学，实医道开卷第一义，学人首当究心焉。
[Diagram of Great Void]
The Great Void (Tai Xu) is the Supreme Ultimate (Tai Ji). The Supreme Ultimate originates from Non-Ultimate (Wu Ji), hence it is called the Great Void. *Tianyuan Ji Dalun* states: "The Great Void is vast and boundless, serving as the foundation for the origin of transformation." This refers to this concept.
The Supreme Ultimate is the beginning of heaven, earth, and all things. *Taishi Tianyuan Ce Wen* states: "The Great Void is vast and boundless, serving as the foundation for the origin of transformation." Laozi said: "Nameless is the beginning of heaven and earth; Named is the mother of heaven and earth." Confucius said: "In Yi there is the Supreme Ultimate, which generates the Two Modes (Liang Yi)." Shao Yong said: "If discussing the Pre-Heaven state, nothing exists; only in the Post-Heaven stage does effort begin." From these observations, we see that in the initial state of the Great Void, it was empty and formless, transforming from non-being to being, where the processes of generation and transformation commenced. Transformation originated from the One, which is named the Supreme Ultimate. Through movement and stillness, the Supreme Ultimate differentiates into Yin and Yang. Thus, heaven and earth consist merely of movement and stillness; movement and stillness are Yin and Yang, and Yin and Yang are the Supreme Ultimate. There is nothing else beyond this. Zhu Xi said: When the Supreme Ultimate is differentiated, it is simply two aspects of Yin and Yang. When Yin Qi flows and spreads, it manifests as Yang; when Yang Qi condenses, it manifests as Yin. Through waxing and waning, advancing and retreating, they undergo infinite changes, creating countless phenomena in the world. Therefore, nowhere is there not Yin and Yang, and nowhere is there not the Supreme Ultimate.
The Supreme Ultimate is essentially Principle (Li). Zhu Xi said: "Before images and numbers take shape, Principle already exists." He also said: "Before heaven and earth existed, this Principle ultimately preceded them." Earlier Confucian scholars said: "There is no Principle outside of Qi, nor is there Qi outside of Principle." Therefore, Principle cannot be separated from Qi, and Qi cannot exist apart from Principle. Wherever Principle resides, Qi resides; wherever Qi moves, Principle moves. Since this Qi exists, it inevitably divides into clear and turbid, thereby establishing the Two Modes. Since there is clear and turbid, it inevitably differentiates into old, young, strong, and weak, thereby forming the Four Images.
Thus, clear and light Yang rises to become Heaven, while heavy and turbid Yin descends to become Earth. Movement and stillness have their mechanisms, and Yin and Yang undergo transformations. From this, the Five Phases (Wu Xing) are distinguished, climatic conditions circulate, spiritual and mysterious phenomena appear, and directional positions are established. Hetu and Luoshu display the fixed numbers of generation and completion, while Bagua Qi preserves the subtle mechanisms of change through odd and even numbers. There is death and there is life, the circulation of creation never ceases; there is ascent and there is descent, the waxing and waning of Qi luck has no beginning or end. Those with constant forms and images can be known, but those with infinite changes are unfathomable. Consequently, the great achieves greatness, and the small achieves smallness. The great establishes heaven and earth; the small encompasses even the tip of an autumn hair. The coherent Principle of the Supreme Ultimate is present everywhere. Thus, the Qi of all things belongs to Heaven and Earth; combined, they form one Heaven and Earth. The Qi of Heaven and Earth constitutes the Five Materials; dispersed, they become myriad heavens and earths. Therefore, without understanding the One, one cannot understand the Myriad; without understanding the Myriad, one cannot speak of Medicine. The study of Principle, Qi, Yin, and Yang is indeed the first principle upon opening the volume of Medicine. Learners must primarily devote their attention to this.