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Taiyang (Greater Yang) is the guiding principle of the Six Channels. Its meridian runs along the back of the body, and its Qi governs the skin and hair of the whole body. Therefore, when diseased, it presents with a floating pulse (Mai Fu), stiffness and pain in the head and neck (Tou Xiang Qiang Tong), and aversion to cold (E Han). This is because the pathogenic factor is confined to the Taiyang channel itself, affecting only the parts traversed by this meridian without involving other channels. If the pathogen is not resolved within the channel, it will subsequently transmit inward to Yangming (the Second Yang) or enter the Three Yin channels. If it enters the Fu organs, it manifests as heat syndrome with a floating and large pulse; if it enters the Zang organs, it manifests as cold syndrome with a deep and fine pulse. As cold and heat stagnate and erupt, various diseases arise, and the pulse and syndromes of Taiyang change accordingly.

If at the initial stage of infection, heat in the Fu organs has not yet arisen and cold in the Zang organs has not yet moved, the condition of Taiyang remains unchanged and symptoms persist. In this case, there are only a floating pulse, stiffness and pain in the head and neck, and aversion to cold. Even if there is a concurrent disease in another channel, as long as the Taiyang condition has not ceased, the pulse and syndromes of Taiyang must still be present. By analyzing the pulse and syndromes of Taiyang to distinguish between Wind-stroke (Zhong Feng) and Cold-injury (Shang Han), one avoids confusion with other channels and prevents getting lost on divergent paths. Zhang Zhongjing’s summary of the Taiyang guideline consists of only this sentence, making the characteristics of Taiyang clear, demonstrating how concise words can capture the essence.

The defining features of Taiyang disease are: floating pulse, stiffness and pain in the head and neck, and aversion to cold.

Since Taiyang governs the exterior, the pulse is floating. Its meridian runs along the back, originating from Jingming (Jingming, an acupoint of the Foot-Taiyang Bladder Meridian located at the inner canthus of the eye), descending from the head to the foot. When diseased, the meridian Qi becomes stagnant and obstructed upward, failing to descend, resulting in stiffness and pain. Wind and cold close off Ying (Nutritive) and Wei (Defensive) Qi, causing Qi stagnation that cannot penetrate and dissipate, thus manifesting externally as aversion to cold. Aversion to cold is the characteristic Qi of the Taiyang channel.

Diseases presenting with fever and aversion to cold originate in the Yang; those without fever but with aversion to cold originate in the Yin. Diseases originating in Yang typically resolve around the seventh day; those originating in Yin typically resolve around the sixth day, based on the numerical attributes of Yang being seven and Yin being six.

This is the general principle for Wind-stroke and Cold-injury. Wei Qi belongs to Yang; Wind injuring Wei Qi is termed "originating in Yang." Injury to Wei Qi obstructs Ying Blood, generating internal heat. Ying Blood belongs to Yin; Cold injuring Ying Blood is termed "originating in Yin." Injury to Ying Blood constricts Wei Qi, generating external cold. Therefore, Wind-stroke initially presents with fever, while Cold-injury initially presents with aversion to cold. Although Wind-stroke involves internal heat, if Ying Blood is not unblocked, external aversion to cold may also appear. Although Cold-injury involves external cold, if Wei Qi fails to reach the surface, fever may subsequently appear. Wind-stroke is not devoid of external cold, but ultimately internal heat predominates over external cold. Cold-injury is not devoid of internal heat, but ultimately external cold predominates over internal heat.

Ying Blood is governed by Liver Wood; as Wood ascends, it transforms into Fire. Wood and Fire share the same nature, so Liver Blood remains warm. Wei Qi is governed by Lung Metal; as Metal descends, it generates Water. Metal and Water share the same nature, so Lung Qi remains cool. The Liver stores Ying Blood, and the Spleen is the root of blood generation. Wind-stroke affecting Ying often leads to decline of Zang Yin, frequently transmitting to Yangming as heat. The Lung stores Wei Qi, and the Stomach is the source of Qi transformation. Cold-injury affecting Wei often leads to weakness of Fu Yang, frequently transmitting to Taiyin as cold.

Wind injuring Wei causes Ying stagnation and interior heat; if Yin within the channel is vigorous, Ying Qi does not steam internally, allowing self-resolution after seven days as the channel cycle completes. Cold injuring Ying causes Wei stagnation and exterior cold; if Yang within the channel is vigorous, Wei Qi does not sink internally, allowing self-resolution after six days as the channel cycle completes. These are favorable courses where Wind-Cold remains in the channels without entering the Zang-Fu organs. However, if Wind-stroke leads to excess Yang entering the Fu organs, or Cold-injury leads to excess Yin entering the Zang organs, Ying and Wei Qi fear internal sinking. Without tonification or purgation to correct the imbalance, timely resolution cannot occur.

Six and seven are the completion numbers of Water and Fire, respectively. According to the Great Expansion Numbers: "Heaven generates One, Earth completes Six" (Water); "Earth generates Two, Heaven completes Seven" (Fire). Thus, Seven is the number of Yang, and Six is the number of Yin. Completing these numbers leads to recovery from illness.