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Wenzhongzi said: "Yi" (medicine) is "Yi" (intent/intelligence); "Yao" (drug) is "Yue" (to dredge/cleanse). This means one must first comprehend the intent of medicine, and then use drugs to dredge and cleanse [the pathogenic factors]. How excellent this statement is! The principle is indeed correct, yet truly comprehending "intent" is extremely difficult. Clinging to a fixed view and attempting to force a patient's condition to conform to one's own theory leads to the fault of stubbornness; liking to display cleverness without thoroughly investigating the established works of ancients is like a military strategist abandoning battle formations or a legal official discarding laws and decrees, leading to the fault of ignorance. According to the former perspective, the issue lies in the inability to apply intent; according to the latter, it lies in the misapplication of intent. Therefore, employing individuals who are unlearned to handle conditions they do not understand or recognize, further fueled by jealousy towards colleagues and a competitive desire for fame and profit, when prescribing medication—how few would avoid the error of adding firewood to save a fire or throwing stones into water? As the saying goes: learning calligraphy wastes paper, but learning medicine wastes people, which refers precisely to this situation.

Mr. You, residing in Jingxian, is a scholar who loves reading and reveres antiquity, yet he devotes his efforts to medicine. Regarding various medical texts from Huangdi (Yellow Emperor) and Qibo onwards, whether morning or night, in cold or heat, he has studied them extensively, penetrating their depths, and organized them through his own understanding. Whenever he gained insights, he recorded them in writing. Over time, the volumes were largely finalized. He analyzes the generation and restriction of the Five Elements (Wu Xing), examines the warmth and severity of the Four Qi (seasonal climates), scrutinizes the yin and yang deficiency and excess in human affairs, as well as the Jun-Chen-Zuo-Shi (Sovereign-Minister-Assistant-Courier) principles of drug properties. For errors inherited in existing books, he clarifies and corrects them; for the chaotic and contentious debates among ancients, he adjudicates and finds the middle ground. Only by reading many ancient books can one skillfully utilize them, avoiding both the misuse and rigid adherence to intent. In this way, one may nearly grasp the essence of Zhang Zhongjing (of Changsha), truly comprehending the intent of medicine.

Furthermore, observing Sima Qian's biography of Bian Que, it states that Changsang Jun gave him all his secret prescriptions, then suddenly disappeared, after which Bian Que could revive the dead. This explanation borders on supernatural matters, and such persons cannot be obtained again. However, in his biography of Chunyu Yi, it states that Chunyu Yi received secret prescriptions from Gongcheng Yangqing and was taught the *Huangdi* and *Bianque Mai Shu* (Pulse Classics) along with five-color diagnosis methods. This illustrates how extensive reading leads to comprehension of intent. I cannot see Bian Que anymore, but being able to see someone like Chunyu Yi would suffice. It is unknown how Mr. You's scholarship compares to the ancients, but his practice of reading extensively and comprehending through intent shows he is inspired by the spirit of the ancients. By using this book to treat diseases, he should certainly not incur ridicule for wasting people's lives!

Preface by Xu Dachun (Lingtai) of Songling, Third Month of Spring, Jiwei Year (1739), 4th Year of Qianlong