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Since Zhang Zhongjing (of Nanyang) first formulated prescriptions, through the Tang, Song, Yuan, and Ming dynasties, up to the current dynasty (Qing), there are countless established formulas. How could one possibly memorize them all? I have often seen practitioners who only study *Qianjin Fang* (Prescriptions Worth a Thousand Gold), or only study *Yi Fang Kao* (Study of Medical Formulas), or only study Zhang Jingyue’s *Xin Fang* (New Formulas), or only study Wu Qian’s *Jie Jie* (Annotations in the Golden Mirror of Medicine). They often adhere to one school while ignoring another, adhering to one source while ignorant of others; this need not be elaborated upon.

I believe that ancient established formulas are like model essays for the imperial examinations; clinical practice is like taking the examination. Even if the topic is identical, one must never copy verbatim. One must grasp the general principle, adapt flexibly, and thus achieve success (cure). Similarly, when facing specific diseases in clinical practice, even if there is an established formula for the disease, one must assess the patient’s constitution (deficiency or excess) and the chronicity of the illness to modify the formula by adding or subtracting herbs.

The essence of formulas lies not in their quantity, but in the skill of modification. For example, *Erchen Tang* (Two-Cured Decoction), composed of Banxia (Pinelliae Rhizoma), Fuling (Poria), Chenpi (Citri Reticulatae Pericarpium), and Gancao (Glycyrrhizae Radix et Rhizoma), treats various phlegm-fluid retention disorders. If Chenpi is removed, it becomes *Haizang Xiaoshu Wan* (Sea-Hiding Summer-Heat Resolving Pill), used for summer-heat with vexation and thirst. This subtraction results in a completely different therapeutic focus. *Pingwei San* (Stomach-Pacifying Powder), composed of Chenpi (Citri Reticulatae Pericarpium), Cangzhu (Atractylodis Rhizoma), Houpo (Magnoliae Officinalis Cortex), and Gancao (Glycyrrhizae Radix et Rhizoma), treats dampness pathogens. If Mangxiao (Natrii Sulfas) is added, it becomes a gynecological formula for expelling the fetus, used for retained dead fetus. This addition leads to a therapeutic aim vastly different from the original. These are methods of addition and subtraction. Do physicians understand this principle?

Furthermore, *Sijunzi Tang* (Four-Gentlemen Decoction) is used for Qi deficiency, and *Siwu Tang* (Four-Agent Decoction) is used for Blood deficiency. In cases of simultaneous Qi and Blood deficiency, combining these two formulas creates *Bazhen Tang* (Eight-Treasure Decoction). This addresses a deeper level of pathology with a correspondingly more potent formula. *Wuling San* (Five-Ling Powder) is used to promote diuresis and resolve dampness, and *Sanshi Tang* (Three-Stones Decoction) is used to clear heat. In cases where dampness and heat are both abundant, combining these two creates *Ganlu Yin* (Sweet Dew Drink). This too addresses a deeper level of pathology with a corresponding adjustment.

Again, *Guben Wan* (Root-Solidifying Pill) treats consumptive fatigue syndromes. By removing Maidong (Ophiopogonis Tuber) and Shengdi (Rehmanniae Radix), it becomes *Sancai* (Three Talents [Formula]), used to treat deficiencies of the Triple Burner. This addresses a milder condition, reducing ingredients to auxiliary roles. *Xiangsu Yin* (Fragrant Perilla Drink) treats common colds occurring in any season. By removing Xiangfu (Cyperi Rhizoma) and Zisu (Perillae Folium), it becomes *Erxian San* (Two-Worthy Powder), used to treat phlegm-fluid retention in the chest diaphragm. This also addresses a milder condition, reducing ingredients to primary roles.

There are countless such examples. Physicians must weigh the situation clinically, subtracting when appropriate and adding when necessary. One must not rigidly adhere to "this disease uses this formula, this formula treats this disease." Only by adapting flexibly can even severe and chronic diseases be cured.