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The generation of all things involves bearing Yin and embracing Yang, achieving harmony through the rushing Qi (vital energy). Therefore, people in ancient times who understood the Great Way modeled themselves on Yin and Yang and harmonized with their techniques and numbers (prescriptive methods for health preservation).

Yin and Yang are the root of techniques and numbers; techniques and numbers are the manifestation of Yin and Yang. Without understanding the Great Way, how can medicine be lightly discussed? The way of medicine is like the walls of a palace. Distinguishing deficiency and excess, examining cold and heat, are the gateways to entry. If the gateway is mistaken, how can one enter the hall and the inner chambers? People who merely browse prescription books and focus on external symptoms consider themselves capable; this is like sleeping and dining only within the gatehouse, unaware of the existence of the hall and inner chambers. Others speak loftily of the *Neijing* (Classic of Internal Medicine) and *Nanjing* (Classic of Difficult Issues), discussing pulse essentials in vain; this is like soaring in the sky above lofty roofs, never glimpsing the profound depths throughout their lives. Although these two approaches differ, their drawbacks are the same. Generally, human life has its origin; thus, the cause of disease also has its origin. Once the origin is clarified, the application of acupuncture and moxibustion, and the formulation of decoctions and fermented wines, are no longer based on subjective speculation or guesswork.

When I first met him in the capital, he appeared humble and modest, seemingly lacking ability. Later, hearing that he was skilled in medicine, I observed that his prescriptions seemed no different from others', yet they were effective immediately upon use. When asked about the reason, he said that the formulas commonly used by people are generally similar, but the standards of weight and lightness, the qualities of rigidity and flexibility, and the appropriateness of sequence are difficult to articulate without true insight. Last winter, due to militia duties, I visited him in Liancheng to inquire about current affairs. His administrative measures for a village or county revealed a clear understanding of the core issues, adapting to local conditions just as one prescribes formulas according to syndromes. He is truly a master of governing the body politic, not engaging in baseless talk. I then requested to read his work *Yi Yuan* (The Origin of Medicine). The book connects beginning and end seamlessly, with clear and lucid text, allowing for immediate comprehension. However, attempting to exhaust its profound meanings often leads to sighs of inadequacy before the vastness. Indeed, once one comprehends the origin, the profound teachings of Qibo, the secret thoughts of Zhang Zhongjing, and the subtle applications of both Chinese and Western medical methods can be integrated into one coherent system. To ascend Mount Tai, one must rely on carriages and horses; to channel the waters at Jishi Mountain, one must rely on boats and ships. Those who pick up fragments from encyclopedic works and forcibly memorize herb properties, making a living as physicians, may find little use for this book. But for those determined to save lives and aspire to reach the level of the ancients who understood the Great Way, this book is indeed the carriage, horse, boat, and ship for physicians. Therefore, I strongly urged its publication and wrote these few words at the beginning to inform students of medicine in the world.

Preface respectfully written by Wu Kuntian, humble younger brother from Qinghe, in the summer of the Xin You year, the 11th year of Xianfeng.