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The key to diagnosing diseases lies in understanding the six characters: Exterior (Biao), Interior (Li), Deficiency (Xu), Excess (Shi), Reversal (Ni), and Compliance (Cong). However, to perceive clearly during clinical practice, one must have thoroughly understood them in advance while studying.

Zhang Zhongjing emphasized the distinction between "Exterior" and "Interior" urgently; however, those who prefer discussing governing principles often do not believe this, arguing that *Ling Shu* and *Su Wen* differentiate symptoms primarily by the Six Channels (Liu Jing) and Zang-Fu organs, asking where there is any mention of "Exterior" or "Interior"? They fail to realize that these two classics were established for acupuncture methods, not for herbal medicine. Acupuncture focuses on selecting acupoints; it only requires examining which channel, Zang organ, or Fu organ is involved, so that techniques such as Giant Puncture (Ju Ci) and Counter Puncture (Miu Ci) can be applied, without urgently distinguishing between Exterior and Interior. In contrast, herbal medicine dictates that light and clear substances are suitable for the Exterior, while heavy and turbid substances are suitable for the Interior. This is the principle. Furthermore, the qi of herbs transforms in the Stomach, is transported by the Spleen, and distributes via the Lungs, similar to food and drink; there is absolutely no logic for them to travel exclusively along a single channel. Therefore, one must distinguish between Exterior and Interior so that therapies such as Sweating (Han), Vomiting (Tu), Purgation (Xia), and Tonification (Bu) can function according to their respective light/clear or heavy/turbid natures. This is precisely why Zhang Zhongjing's terminology differs from that of *Ling Shu* and *Su Wen*.

Regarding "Deficiency" and "Excess," there are two meanings: first, presence of pathogenic factors constitutes Excess, absence constitutes Deficiency; second, accumulation of pathogenic factors constitutes Excess, non-accumulation constitutes Deficiency. Both refer to conditions requiring the draining of pathogens, not the application of tonification. One should read the relevant chapters to verify that my words are not absurd.

Regarding "Reversal" and "Compliance," these concepts appear in complexion, pulse, signs/symptoms, and treatment. One must first accurately determine the disease before discussing these aspects. If one can mystically illuminate these principles, life and death prognoses can be decided.

Both *Ling Shu* and *Su Wen* refer to all diagnoses involving body heat as Heat Disease (Re Bing). Thus, in *Su Wen*, Labor Wind (Lao Feng) and Kidney Wind (Shen Feng) are evaluated together after Warmth (Wen); in *Ling Shu*, sensations like insects crawling and Jaundice (Dan) are listed alongside Heat Within (Re Zhong). Those scattered in other chapters are too numerous to count. Generally, this classification is based on what can be diagnosed, not on etiology; how can it be exclusively defined by Cold Damage (Shang Han) transforming into Warmth? For the symptom of body heat, listing the most typical cases and exploring their categories—detailing the typical and appending the similar—is indeed appropriate. This aligns with Zhang Zhongjing’s discussion of Shang Han which includes Dampness (Shi) resembling Shang Han. Superficial scholars often discuss Warm-Heat (Wen Re) diseases by citing the Heat Treatises of both classics, adopting some and discarding others, but does this truly accord with the source of disease? When they speak of "Shu" (Summerheat), they interpret it merely as "Heat"; passages in *Su Wen · Tong Tian* such as "affected by Shu" and "Shu Jie" in *Gu Kong Lun* do not refer to summer heat. To classify them as summer diseases based on *Tong Tian* is to fundamentally misunderstand the canonical intent. When they speak of "Wen," they interpret it as "accumulation/hidden." The statement in *Su Wen · Re Bing* "diseases occurring before the Summer Solstice are called Wen" implies that after the Summer Solstice, weather is hot, making people susceptible to external pathogens, hence termed "Heat"; before the Summer Solstice, weather is not yet hot, so people are less susceptible, thus naming it based on internal accumulation. "Wen" retains its original meaning, unlike modern interpretations defining it as "mild heat." Do we not observe patients suffering from Spring Warmth (Chun Wen)? Their fever is intense and blazing; how could this be mild heat? If one does not understand the principles and examples when reading, ancient methods will be entirely lost.