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In all cases of Shaoyang disease (diseases caused by cold pathogens), the root cause is injury by cold qi, with wind acting as the commander of cold. However, when distinguishing wind and cold by their seasonal commands, wind governs spring and the east, while cold governs winter and the north; when distinguishing them by severity and depth, wind belongs to Yang and is superficial, whereas cold belongs to Yin and is deep. Nevertheless, wind brings cold along, and cold enters following wind, penetrating bones and invading muscles, essentially sharing the same nature. Therefore, shallow cold constitutes Shangfeng (Wind Injury); deep wind constitutes Shanghan (Cold Damage); neither shallow nor deep, existing in a state between upright and pathogenic, constitutes Nueji (Malaria); if it remains in the meridians causing limb pain, it becomes Fengbi (Wind Bi). Thus, Shangfeng, Shanghan, Nueji, and Fengbi are all caused by wind and cold. Observing the *Lingshu · Jiugong Bafeng Chapter* and the *Suilu Lun*, both emphasize the harm of Xuexi Zeifeng (Empty Evil and Robber Wind). The *Kouwen Chapter* states that "wind becomes cold-heat," referring to wind as cold evil. Just as being injured by cold in winter should rightly be called Shanghan, what about cold damage contracted in spring, summer, and autumn? Are they not due to cold, and do they not enter via wind? Thus, Zhang Zhongjing said: "All diseases of Shanghan mostly arise from wind and cold. Initially, wind-cold affects the exterior; if it enters the interior, it will not dissipate on its own. If one keeps warm and covered, there is no case where it does not dissipate. Is this not proof that wind and cold share the same nature?" The *Neijing* states: "Carefully observe and avoid empty wind." Therefore, the sages taught that the way to avoid empty evils is like avoiding arrows and stones, so that evil cannot harm the body. This is referred to as preventing problems before they arise.

The disease of Shanghan arises largely from severe cold in winter. During times when water freezes and earth cracks, there is an abundance of Shaoli qi (killing and harsh qi). When people encounter it and fall ill immediately, this is Zheng Shanghan (True Cold Damage), which is the syndrome of Yin-cold directly striking the interior. However, this occurs mostly in times of displacement and poverty. In times of peace, when people are secure, well-fed, and warm, direct-striking diseases are rare. This is the first type of Shanghan. There are those who contract cold in winter but do not fall ill immediately; the cold toxin hides between Ying (Nutritive) and Wei (Defensive) qi. When spring and summer arrive, encountering wind and cold again causes the pathogenic qi to activate according to the season. Thus, in spring it manifests as Wenbing (Warm Disease), and in summer as Shubing (Summerheat Disease). Therefore, hardworking people often suffer from warm-heat diseases in spring and summer because they were injured by cold in winter. These conditions change with the transmission of qi and do not belong to immediate-onset True Shanghan. Treatment should follow the symptoms of cold and heat. This is the second type of Shanghan. Furthermore, there are Shixing zhiqi (Seasonal Epidemic Qi). For example, spring should be warm but is cold; summer should be hot but is cool; autumn should be cool but is hot; winter should be cold but is warm. Having such qi out of season results in many people, young and old alike, suffering from similar illnesses throughout the year. This is Shixing bing (Seasonal Epidemic Disease), caused by contracting abnormal empty wind. It manifests immediately upon contraction. Those with weak constitution who are careless with daily life and prone to fatigue are easily affected. This is the third type of Shanghan. All three types belong to Shanghan, but their manifestations differ, and treatments vary in depth. Failure to distinguish them will inevitably lead to misdiagnosis and harm to patients.