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Among the nine schools of thought, none is more difficult than medicine, nor is any more demanding of caution, for human life and destiny depend upon it. Therefore, one must receive transmission from a master teacher, exhaustively study principles through long-term practice, and maintain a humble and cautious mind during clinical application. Upon encountering a patient's illness, one must first examine the individual's constitution, assess their temperament, and consider their living environment and habits. By tracing the meridians and collaterals, one identifies the root cause of the disease and its location. Subsequently, by aligning with seasonal changes and geographical conditions, and prescribing medication based on pulse diagnosis and symptoms, efficacy is invariably achieved promptly.

However, since Zhang Zhongjing, renowned physicians have emerged generation after generation, and their written works are as numerous as books filling warehouses or causing oxen to sweat (a metaphor for an immense volume of literature). For later scholars immersed in this vast sea of medical texts, unless they bury themselves in reading, deeply contemplate the underlying meanings, and receive guidance from a master teacher, few can truly grasp the essence. In my youth, I paid attention to prescription books and gained some knowledge of materia medica. Whenever I fell ill, I refrained from taking medicine lightly, fearing misdiagnosis by incompetent physicians.

I was now appointed by the Holy Son of Heaven to serve as Governor of Guangdong. Guangdong is a region characterized by mountains and seas. In astronomical star divisions, it corresponds to the Chunhuo sector; its climate is predominantly dry, yet being close to the ocean and surrounded by layered mountains, its streams, ravines, and springs are inherently damp. In such a place where the sky is dry and the earth is damp, those who live there without self-discipline will immediately fall ill. Those with robust vital energy may experience mild pathogenic invasion with rapid onset, potentially recovering without medication. However, severe cases require medical intervention. It is surprising that among physicians in Guangdong, fewer than one in ten can recite *Tangtou Gejue* (Song Formulas) or are familiar with *Maijue* (Pulse Rhymes); many do not even understand what the *Neijing* (Inner Canon) is or the meaning of *Tiaobian* (Delineations). Slightly knowing drug properties, they rigidly adhere to old prescriptions. Lacking internal understanding and clear diagnostic skills, their prescriptions often result in death.

Current diseases involve distinctions between cold and heat, exterior and interior, similarities and differences, and variations in depth and primary versus secondary factors. For symptoms resembling heat, cool formulas are often administered. Yet, one must realize that pathogenic cold manifesting as heat requires warming methods to resolve; administering cool formulas is akin to wielding a sharp blade. For symptoms resembling cold, warm formulas are often used. However, food stagnation causing internal steaming can lead to extreme heat presenting as false cold, with all six pulses hidden; this requires purgative methods. Administering warm formulas here is even more like wielding a sharp blade. What is most shocking is the indiscriminate use of expensive herbs such as Guizhi Tang (Cinnamon Twig Decoction), Fuzi (Prepared Aconite Root), and Renshen (Ginseng Root), regardless of the patient's constitution, seasonal climatic factors, or the root cause of the disease. Physicians believe that using expensive herbs signifies mastery and experience, unaware that they are killing patients under the guise of treatment while refusing to acknowledge their guilt. Such incompetence is unparalleled.

During my less than three years as Governor of Guangdong, the number of deaths caused by physicians has been incalculable. I deeply pity the people of Guangdong for blindly entrusting their lives to incompetent physicians without realizing it. Later, Yu Zi'an from Shanyin arrived in Guangdong, bringing with him a secret copy of *Bianzheng Lu* (Record of Syndrome Differentiation). I borrowed it to read and found that it contained insights surpassing those of Zhang Zhongjing and other predecessors. Its syndrome differentiation, compromise, and supplementation constitute a supreme treasure for benevolent individuals seeking to save the world. I therefore donated my salary to have this book printed and widely distributed, hoping that physicians in Guangdong would study it diligently, comprehend its correct principles, and thus I have not hesitated to write this preface despite its triviality.

Written by Nian Xiyao, a native of Guangning, Right Vice Censor-in-Chief of the Censorate, Imperial Commissioner Governing Guangdong and Other Regions, Commander-in-Chief of Military Affairs, and Administrator of Grain and Supplies, in the year Yisi of the third year of the Yongzheng Reign of the Great Qing Dynasty.