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I have often heard that the practice of medicine relies on "Yi" (the physician's intuition and insight). Generally, the causes of disease in humans vary into wind, cold, summer-heat, dampness, as well as overwork or idleness; the flavors of medicines differ into sour, bitter, pungent, salty, sweet, and bland. Unless one possesses the realms of Shen (Divine), Sheng (Sage), Gong (Skillful), and Qiao (Clever), how can one measure the syndromes of exterior-interior and deficiency-excess? How can one examine the pulse qualities of floating, sunken, slippery, and rapid? The changes in conditions follow favorable or adverse patterns, presenting in thousands of forms. The key lies in adapting treatment to the specific disease and responding flexibly at the moment of clinical decision-making. Medication should not be rigidly bound to fixed prescriptions but adjusted according to time and condition. One must distinguish the warming, cooling, cold, and hot properties of drugs, assess the urgency and severity of the illness, determine the roles of Sovereign (Jun), Minister (Chen), Assistant (Zuo), and Envoy (Shi) in herbal compatibility, and thus formulate prescriptions for treatment. Without profound attainment and a clear understanding of medical mysteries, how could one achieve this?

Dai Yuanli, the Director of the Imperial Medical Bureau of our dynasty, comprehended the medicinal properties explored by Shennong, investigated the principles found in the Huangdi Neijing (Yellow Emperor's Inner Canon), clarified the methods of Yin Yi's decoctions, examined the essentials of Wang Shuhe's pulse diagnosis, and mastered the secrets of tonification and purgation developed by Li Dongyuan. Therefore, whenever he treated diseases, his adjustments of medications yielded miraculous effects. Even Bian Que and Hua Tuo of ancient times would not surpass him. Moreover, he lived in an enlightened era, served a sage sovereign, led the medical profession, and spread his fame across the four seas. He held a heart that upheld righteousness without seeking profit, illuminated the Dao without calculating merit, and solely focused on saving lives. He once compiled two volumes titled *Zhengzhi Yaojue* (Essentials of Syndrome Differentiation and Treatment) and *Leifang* (Classified Formulas), keeping them hidden in chests with great secrecy. Only Zuan Xixu, a monk residing at Lingyin Temple and abbot of Yongle Temple, shared a deep friendship with him outside worldly affairs and occasionally glimpsed these works. Out of love for them, Zuan Xixu copied them and treasured them, wrapping them carefully layer by layer.

In the Xin You year of the Zhengtong era, Censor Chen Yi toured Zhejiang as an imperial inspector. Arriving in Cixi, Ningbo, and passing through Yongle Temple, Zuan Xixu noted that Chen's grandfather had once served as the county magistrate there, whose virtuous governance was still praised today. Thus, their relationship became warm and cordial. Zuan Xixu showed him the secretly kept medical books. Master Chen read them thoroughly, unable to put them down. Savoring the discussions and judgments, he found novelty within established rules and saw extraordinary insights at the extreme of logical interest. Observing the subtlety of adjusting medications according to the disease, it was not only that the drugs were extremely precise, but also that the treatments were well-founded. This is indeed the compass and square of the medical gate. Those who wish to master the standards of medicine in the future, should they not take this as their model?

Now, having obtained this book, Master Chen regards it as a supreme treasure. Eager to have it carved onto woodblocks and widely disseminated, he requested me to write a preface, recording the origin of his acquisition and his benevolent intention to benefit others. His desire to help people and assist all beings is truly profound! I consider that Master Chen descends from a noble family, accumulates virtue and performs good deeds, and exerts himself fully in anything beneficial to others. For instance, earlier this spring, several fishermen from Joseon (Korea) went out to sea fishing, were blown off course by the wind to Zhejiang. The local military mistook them for Japanese pirates, captured them, and sent them to the capital to be detained. They suffered from hunger, cold, and hardship. Only Master Chen pitied them, providing complete clothing and food supplies so that none were left destitute, and eventually they returned home safely. His mindset and conduct are generally like this. If this book is published and circulated throughout the world and future generations, not only will people rely on the *Essentials* to escape severe illnesses, but many who would otherwise die young or violently will surely attain longevity. His contribution to the medical way and his virtue of alleviating the suffering of the people—can such merits be considered shallow?

On the fourth day of the eleventh month of the Gui Hai year, the eighth year of the Zhengtong era, Hu Ying, Grand Master of Virtue, High Minister of State Affairs, Minister of Rites, former Guest of the Crown Prince, and Chancellor of the Imperial Academy, from Piling, wrote the preface.