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Diseases have fixed patterns, hence the Six Channels (Six Stages) are established to govern them respectively; diseases also undergo changes and transformations, thus one must further refer to combined diseases (Bingbing) and concurrent diseases (Hebing) for mutual reference. This represents the perfection of Zhang Zhongjing's two methods. Yin and Yang are mutually rooted; although Qi is divided into the Three Yang and Three Yin, the Shen (Spirit/Mind) naturally unites. The interior of the Three Yang channels is the Three Yin channels, and the exterior of the Three Yin channels is the Three Yang channels. For instance, if a Taiyang disease (disease of the Taiyang channel) presents with a sunken pulse, it combines with Shaoyin disease (disease of the Shaoyin channel); if Shaoyin disease presents with fever, it combines with Taiyang disease. If Yangming disease (disease of the Yangming channel) presents with a slow pulse, it combines with Taiyin disease (disease of the Taiyin channel); if Taiyin disease presents with a moderate pulse, it combines with Yangming disease. If Shaoyang disease (disease of the Shaoyang channel) presents with a fine and small pulse, it combines with Jueyin disease (disease of the Jueyin channel); if Jueyin disease presents with a faint and floating pulse, it combines with Shaoyang disease. Although there is no name for "combination," there is the reality of combination. Sometimes Yang resolves through Yin, or Yin resolves through Yang; sometimes Yang enters Yin leading to danger, or Yin loses Yang leading to rebellion. Various pulses and symptoms cannot be enumerated. Students should examine whether the disease trend is combined within the Yin and Yang syndromes, and further scrutinize whether the symptoms are concurrent or overlapping among the Three Yang and Three Yin. By applying methods such as treating Yang diseases via Yin, treating Yin diseases via Yang, supporting Yang to suppress Yin, and draining Yang to tonify Yin appropriately, treatment can be effective.

The Three Yang channels all present with fever, and the Three Yin channels all present with diarrhea. If both fever and diarrhea occur, it is a Yin-Yang combined disease. In Yin-Yang combined diseases, if Yang is excessive, it belongs to the Yang channels, and the diarrhea is due to excess heat. Examples include Taiyang-Yangming combined disease, Yangming-Shaoyang combined disease, and Taiyang-Shaoyang combined disease, which inevitably cause spontaneous diarrhea; these are treated with formulas like Gegen Tang (Kudzu Decoction) and Huangqin Tang (Scutellaria Decoction). If Yin is excessive, it belongs to the Yin channels, and the diarrhea is due to deficiency cold. Examples include Shaoyin disease with vomiting, diarrhea, and fever (which is not fatal), or Shaoyin disease with diarrhea of undigested food, presenting with interior cold and exterior heat, aversion to cold absent but with a red complexion; these are treated with Tongmai Sini Tang (Pulse-Regulating Four Reversals Decoction). If Yang combines with Yang without involving Yin, it is a Three Yang combined disease, presenting with spontaneous sweating but no diarrhea, corresponding to the Baihu Tang syndrome (White Tiger Decoction pattern). If Yin combines with Yin without involving Yang, it is a Three Yin combined disease, presenting with no fever but with vomiting, diarrhea, and cold extremities, corresponding to the Sini Tang syndrome (Four Reversals Decoction pattern).

Concurrent disease (Bingbing) differs slightly from combined disease (Hebing): Hebing refers to symptoms appearing simultaneously, while Bingbing refers to symptoms succeeding one another. For example, if the headache and stiff neck of Taiyang disease have not yet resolved, and subsequently a wiry pulse, dizziness, and epigastric fullness/stiffness appear, this is a concurrent disease with Shaoyang disease. If delirium also appears, it becomes a concurrent disease of the Three Yang. In Taiyang-Yangming concurrent disease, if Taiyang symptoms persist, treat with mild diaphoresis from the Taiyang perspective; if Taiyang symptoms have resolved, treat with purgation from the Yangming perspective. The key distinction lies in the presence or absence of aversion to cold and fever. However, Yangming disease fundamentally involves stomach excess (Wei Jia Shi - gastric organ excess/heat accumulation). In Taiyang-Yangming combined disease, if there is wheezing and chest fullness, purgation is contraindicated, lest the stomach excess is not yet fully formed. If Yangming disease combines with Taiyin and Shaoyang, causing spontaneous diarrhea, how can it still be called Yangming disease? One must understand that "diarrhea accompanying heat" (Xie Re Xia Li) is the beginning of stomach excess. As stated in the *Neijing* (Inner Canon), "acute watery diarrhea with tenesmus belongs to heat." The pulse will necessarily be floating, large, or wiry-large, allowing it to be attributed to Yangming rather than Taiyin. Conversely, if there is diarrhea of undigested food, interior cold with exterior heat, and a floating yet slow pulse, the floating aspect does not belong to the exterior, and the slowness indicates disease in the Zang organs. If the pulse is faint and nearly imperceptible, even if there is no aversion to cold but a red complexion, it should be attributed to Shaoyin disease. The differentiation between Taiyin and Yangming diarrhea lies in whether undigested food is passed. Furthermore, when both Taiyin and Shaoyin present with diarrhea of undigested food, the differentiation relies on whether the pulse is slow or faint. Yangming governs stomach excess but may present with diarrhea accompanying heat; Taiyin governs diarrhea of undigested food but may be attributed to Shaoyin due to a faint and fine pulse. A faint pulse with diarrhea, yet presenting with Yangming signs of no aversion to cold and a red complexion, requires reference to combined diseases to understand such complex disease progression and apply appropriate treatment. Thus, the combinations of the Six Channels and the combinations of internal injury versus external contraction, if understood spiritually and clearly, are inexhaustible. By perceiving the function of Yin-Yang separation and union through their mutual rooting, one realizes that the principles of the Six Channels are definitive yet flexible, not rigidly fixed. How can one casually claim that there are no combined diseases in the Three Yin channels?