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Zhang Zhongjing’s classic is named "Shanghan" (Cold Damage). Here, "Shanghan" serves as a general term for external contraction diseases. Among the various categories of Shanghan, there is a specific type known as Taiyang disease (disease of the Taiyang channel). Its manifestations include: either fever has already appeared, or it has not yet appeared, but there must be aversion to cold, heaviness of the body, vomiting and regurgitation, and a tight pulse at both yin and yang positions (cun and guan). Only this specific presentation is uniquely termed "Shanghan."

Both "Shanghan" (Cold Damage) and "Zhongfeng" (Wind Strike) present with Taiyang disease symptoms such as headache, stiffness of the head and neck, and aversion to cold, and both exhibit a floating pulse. They are most easily confused and thus require careful differentiation. A pulse that is floating and slow, accompanied by spontaneous sweating, indicates an etiology of wind. A pulse that is floating and tight, without sweating, indicates an etiology of cold. Wind damages Wei Qi (Defensive Qi), while cold damages Ying Blood (Nutritive Blood). The boundary between Ying and Wei is extremely strict; errors in identification are inadmissible. However, Wang Shuhe, in his Preface to the Examples, stated that most Shanghan diseases arise from wind and cold, conflating wind and cold without distinction, let alone differentiating them from warm-heat diseases. He further stated that those who contract illness immediately during the severe cold of winter are named "Shanghan." Regardless of whether Zhang Zhongjing held this view at the time, even if one specifies that only winter-onset cases constitute true "Shanghan," consider a scenario during severe cold where a patient presents with Taiyang disease characterized by headache and fever. If this patient has a slow pulse with spontaneous sweating, or exhibits only fever without aversion to cold and with thirst, should they all be treated according to Zhang Zhongjing’s principle of inducing heavy sweating? In such cases, misdiagnosis would be nearly inevitable. Thus, should treatment follow the season or the syndrome? The confusion deepens. Ultimately, Zhang Zhongjing’s flexible and adaptive methods were never rigidly bound to seasonal discussions of disease. Instead, he instructed practitioners to identify pathogenesis through pulse analysis and syndrome differentiation. For Taiyang disease, regardless of whether fever is present, if there is aversion to cold, body heaviness, vomiting/regurgitation, and a tight pulse at both yin and yang positions, this constitutes true cold damaging Ying Blood. With such accurate differentiation, one will not confuse wind with cold, nor allow heat to disrupt the understanding of cold.

In Shanghan diseases, some present with fever, but the pathogen does not remain in the Taiyang channel but directly enters the Yin channels. Among the Three Yin channels, Shaoyin disease is most easily confused with Taiyang disease. This is because the Taiyang Bladder and the Shaoyin Kidney share a zang-fu exterior-interior relationship. In individuals with inherent deficiency of Yin essence, cold pathogens may bypass the transmittal process from the exterior to the interior and directly invade the Kidney from the Bladder fu-organ. Therefore, regarding the syndrome treated by Da Qing Long Tang (Major Green Dragon Decoction), where the Shanghan pulse is floating and slow, the body is not painful but feels heavy, occasionally alleviating, Zhang Zhongjing insisted on distinguishing the absence of Shaoyin syndrome before administering heavy sweating therapy. If mistakenly applied to Shaoyin disease, the True Yang within the Kidney would dissipate with the sweat; how can one not be cautious?

Taiyang Shanghan typically presents with a floating-tight pulse, or occasionally a floating-slow pulse if wind factors are involved. Conversely, Shaoyin disease presents with a sunken, thready, and fine pulse. For Shaoyin disease presenting with initial onset, counter-current fever, and a sunken pulse, Zhang Zhongjing specifically formulated Ma Huang Fu Zi Xi Xin Tang (Ephedra, Aconite, and Asarum Decoction). This is because Aconite is required to stabilize the True Yang in the Kidney, allowing Ephedra and Asarum to guide the Shaoyin pathogen out to the exterior. When cold pathogens initially attack Taiyang and gradually transmit through the channels into the Three Yin channels, the presentations often involve mixed cold and heat patterns, not necessarily attributable solely to cold etiology. Various rescue methods exist: some resolve from the interior, others from the exterior, each tailored to the specific syndrome. If cold pathogens directly enter the Three Yin channels without any exterior signs, symptoms may include vomiting and diarrhea, cold extremities, or restlessness—various critical conditions where the pivot of life and death hangs in the balance. In such cases, potent Yang-restoring decoctions must be urgently administered to break through obstructions, recover True Yang, and swiftly dispel yin-cold. Any delay renders the condition incurable. Zhang Zhongjing’s major principles are rigorously documented; who claims that Shanghan diseases can be universally treated by exterior-dispersing methods?