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Examining the nature of all things, there are always association and dissociation. When a tiger roars, wind arises; when a dragon chants, clouds gather; lodestone attracts iron needles; amber picks up mustard seeds; lacquer disperses upon contact with crabs; hemp swells upon contact with lacquer; cinnamon twig becomes soft when combined with scallion; trees wither when exposed to cinnamon; halite can be stacked like eggs; otter gall divides a cup of wine. Their qi is mutually responsive and interconnected, mostly following such patterns, and their principles are difficult to fully comprehend through thought alone. As for various medicinal materials, they particularly influence each other in terms of benefit and harm. The sages have already clearly stated certain rules; how can one fail to investigate them in detail and avoid pitfalls? Contemporary practitioners compiling prescriptions often omit details. If an old prescription contains a condition that should be modified or removed, it ought to be adjusted. If two substances have comparable interactions (referring to mutual aversion or incompatibility), one should select and remove one based on the severity of the condition. In the Chisan Decoction for treating Cold Damage, I usually exclude Veratrum Viride Rhizome (Lilü, 藜芦); in the Huanglian Wan for dysentery, I also remove Zingiberis Preparata Rhizome (Ganjiang, 干姜), yet the efficacy is invariably achieved. Why insist on forcing substances that mutually detest each other to coexist? The harm caused by incompatibility (Xiangfan, 相反) is deeper than that of mutual aversion (Xiang'e, 相恶). Mutual aversion means that although they dislike each other, there is no resentment; for instance, Niuhuang (Calculus Bovis, 牛黄) dislikes Gulonggu (Os Draconis, 龙骨), but Gulonggu becomes more effective when combined with Niuhuang because one controls the other. Incompatibility means they are like enemies and must not be combined. Modern painters note that Realgar (Xionghuang, 雄黄) and Lead White (Hufen, 胡粉) placed near each other appear dull and jealous; powder turns black when mixed with realgar, and realgar changes when mixed with powder; this is evidence of incompatibility. Since pharmacological principles are unclear, efficacy is poor, and people often disregard them. Now, when prescribing according to formulas, it may be difficult to consult the Materia Medica immediately. Therefore, I copy these matters here for reference. A brief reading makes verification easy. However, in the *Shennong Bencao Jing* (*Divine Farmer's Materia Medica*), items like Zhuyu (Corni Fructus, 茱萸) and Mendong (Ophiopogonis Radix, 麦冬) are listed without distinguishing between Shan Zhuyu (Corni Fructus, 山茱萸) and Wu Zhuyu (Zanthoxyli Fructus, 吴茱萸), or between Tianmendong (Asparagi Radix, 天门冬) and Maimendong (Ophiopogonis Radix, 麦门冬). Each entry should be clearly labeled. There are also errors and confusions; for example, Haige (Concha Arcae, 海蛤) and Haiheli (Concha Arcae, 海蛤壳) have identical avoidance relationships. Also, various Zhi (Ganoderma spp., 灵芝) interact with Shuyu (Dioscoreae Rhizoma, 薯蓣), and Shuyu interacts with Zizhi (Ganoderma Sinense, 紫芝); calculations suggest this should not occur, but since it is unknown which is correct, both are recorded for future verification. Furthermore, the *Shennong Bencao Jing* states that "mutual enhancement" (Xiangshi, 相使) applies to specific pairs; cross-referencing with drug pairs reveals two or three instances, which poses no objection. Those described as "mutual accord" (Xiangde, 相得) to treat diseases together are not contraindicated and thus are not separately listed.

The Upper Grade consists of 120 herbs acting as Sovereign drugs, primarily nourishing life to align with Heaven. They are non-toxic; long-term use does not harm the body. For those seeking to lighten the body, augment qi, prevent aging, and prolong life: these Upper Grade herbs can also dispel disease, but their action is gentle and profound, lacking immediate effects. However, consistent use over time yields great benefits. Once illness is cured, life is extended. Heaven’s way is benevolent nurturing, hence "aligning with Heaven." The number 120 corresponds to the months of Yin, Mao, Chen, and Si, modeling the time when all things grow and flourish.

The Middle Grade consists of 120 herbs acting as Minister drugs, primarily cultivating temperament to align with Humanity. They may be toxic or non-toxic, used with careful judgment. For those aiming to suppress disease and tonify emaciation: the therapeutic descriptions for Middle Grade herbs are more intense, while claims of lightening the body are weaker. For users, disease removal is relatively fast, while longevity extension is slower. Humans possess temperament, hence "aligning with Humanity." The number 120 corresponds to the months of Wu, Wei, Shen, and You, modeling the time when all things mature.

The Lower Grade consists of 125 herbs acting as Assistant and Envoy drugs, primarily treating disease to align with Earth. They are mostly toxic and should not be taken long-term. For those aiming to eliminate cold-heat pathogenic factors, break up accumulations, and cure illness: Lower Grade herbs specialize in attack. Their toxic and fierce qi damages the harmonious balance and cannot be taken continuously; usage stops once the disease is resolved. Earth’s nature is收敛 (restraining) and killing, hence "aligning with Earth." The number 125 corresponds to the months of Xu, Hai, Zi, and Chou, modeling the time when all things wither and store. This includes leap month adjustments. The *Shennong Bencao Jing* lists 365 items across the three grades, corresponding to the 365 degrees of the year, one degree per day, completing a year. The current outline clarifies the classification numbers. Herbs added later by famous physicians or included in Tang dynasty commentaries are excluded from this count.