生生子曰∶天地间非气不运，非理不宰，理气相合而不相离者也。何也？阴阳、气也，一气屈伸
而为阴阳动静，理也。理者、太极也，本然之妙也。所以纪纲造化，根柢人物，流行古今，不言之蕴
也。是故在造化，则有消息盈虚∶在人身，则有虚实顺逆。有消息盈虚，则有范围之道；有虚实顺逆，
则有调剂之宜。斯理也，难言也，包牺氏画之，文王彖之，姬公爻之，尼父赞而翼之，黄帝问而岐伯陈之
，越人难而诂释之，一也。但经于四圣则为《易》，立论于
岐黄则为《灵》、《素》，辨难于越人则为《难经》，书有二而理无二也。知理无二，则知《易》以道阴
阳，而《素问》，而《灵枢》，而《难经》，皆非外阴阳而为教也。《易》理明，则可以范围天地，曲
成民物，通知乎昼夜；《灵》、《素》、《难经》明，则可以节宣化机，拯理民物，调燮札瘥疵 而登太和
。故深于《易》者，必善于医；精于医者，必由通于《易》。术业有专攻，而理无二致也。斯理也，难言
也，非独秉之智不能悟，亦非独秉之智不能言也。如唐祖师孙思邈者，其洞彻理气合一之旨者欤，其深
于《易》而精于医者欤，其具独秉之智者欤。故曰∶不知《易》者，不足以言太医；惟会理之精，故立论
之确，即通之万世而无敝也。彼知医而不知《易》者，拘方之学，一隅之见也；以小道视医，以卜筮视
《易》者，亦蠡测之识，窥豹之观也，恶足以语此。
Shengshengzi said: In the world between heaven and earth, without Qi (vital energy), there is no movement; without Li (principle), there is no governance. Li and Qi combine and cannot be separated. Why? Yin and Yang are forms of Qi; the flexion and extension of one Qi constitute the dynamic and static states of Yin and Yang, which is Li. Li is Taiji (Supreme Ultimate), the inherent mystery of original nature. It serves as the guiding principle for creation, the foundation of all beings, flowing through past and present, an unspoken profundity. Therefore, in creation, there are waxing and waning, fullness and emptiness; in the human body, there are deficiency and excess, smoothness and reversal. With waxing and waning, there is a way to regulate; with deficiency/excess and smooth/reversal, there is an appropriateness to adjust. This Li is difficult to describe. Fuxi drew the trigrams, King Wen composed the Tuan commentaries, the Duke of Zhou wrote the Yao lines, Confucius praised and supported them, the Yellow Emperor asked, and Qibo expounded, Bian Que (Yue Ren) raised difficulties and explained them—all pointing to the same truth. For these four sages, discussing Yi resulted in the *Book of Changes* (*Yijing*); establishing theories in Qibo-Huangdi medicine resulted in the *Ling Shu* (Spiritual Pivot) and *Su Wen* (Basic Questions); resolving difficulties by Bian Que resulted in the *Nan Jing* (Classic of Difficult Issues). The books differ, but the principles do not. Knowing that principles are undivided, one understands that the *Yijing* elucidates Yin and Yang, and thus the *Su Wen*, *Ling Shu*, and *Nan Jing* also do not establish their teachings apart from Yin and Yang. If the principles of Yi are clear, one can regulate heaven and earth, fully accomplish all things, and understand day and night; if the *Ling Shu*, *Su Wen*, and *Nan Jing* are clear, one can regulate and disseminate the mechanisms of transformation, save and govern the people, harmonize epidemics and diseases, and attain supreme harmony. Thus, those profound in Yi must be skilled in medicine; those refined in medicine must have attained understanding through Yi. Professions have their specializations, yet the principles are consistent. This Li is hard to speak of; it requires unique wisdom to comprehend, and unique wisdom to articulate. Take Sun Simiao, the Patriarch of the Tang Dynasty, as an example. Was he not one who thoroughly penetrated the purport of the unity of Li and Qi? Was he not profound in Yi and refined in medicine? Was he not endowed with unique wisdom? Hence it is said: "One who does not know Yi is not qualified to discuss Great Medicine." Because he mastered the essence of principles, his theories were precise, remaining valid for ten thousand generations without flaw. Those who know medicine but not Yi engage in the learning of rigid prescriptions, holding a partial view; regarding medicine as a minor art and Yi as mere divination reflects the shallow insight of measuring the sea with a gourd shell or viewing a leopard through a tube. How could such people discuss this?