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Ren Yingqiu: The Seven Meanings of “Xu” and “Shi” in TCM
What do “Xu” (虚) and “Shi” (实) really mean?
“Xu” and “Shi” refer to the nature of pathological changes, and they are an extremely important aspect of syndrome differentiation.
Thus, “Xu” indicates supplementation, while “Shi” indicates purging, which are essential methods for differentiation and treatment; supplementation leads to “Shi”, while purging leads to “Xu”, which are the inevitable results of accurate differentiation and treatment. However, understanding the “Xu” and “Shi” of pathological changes and the methods of supplementation and purging is relatively easy at a superficial level, but achieving precise differentiation and application is quite challenging.
Based on literature and clinical experience, the meanings of “Xu” and “Shi” are summarized as follows for research purposes, which may assist in syndrome differentiation and treatment.
When analyzing the “Xu” and “Shi” of pathological changes during syndrome differentiation, there are various meanings that should not be confused, as this would affect the accuracy of differentiation. Upon detailed analysis, there are approximately the following categories:
1. Differentiation of “Xu” and “Shi” based on the strength of Zheng Qi (正气)
In the “Shang Han Lun (Treatise on Cold Damage) – Ping Mai Fa (Method of Pulse Diagnosis)” it states: “When the pulse comes quickly and leaves slowly, this indicates internal “Xu” and external “Shi”. When the pulse comes slowly and leaves quickly, this indicates internal “Shi” and external “Xu”.
Zhou Chengzhi explains in the “Bian Ping Mai Zhang Ju (Commentary on Pulse Diagnosis)” that: “The coming and going refers to the entry and exit of the pulse; entry and exit refer to the internal and external aspects of Yin, Yang, blood, and Qi. A quick coming and slow going indicates more exit and less entry, thus Qi gathers externally, hence external “Shi”; a slow coming and quick going indicates less exit and more entry, thus Qi gathers internally, hence internal “Shi”. External “Shi” indicates weak Yin absorption, hence internal “Xu”; internal “Shi” indicates weak Yang propulsion, hence external “Xu”.”
The entry and exit of pulse Qi, whether Yin or Yang, all belong to the category of Zheng Qi. Therefore, the “Xu” and “Shi” mentioned here refer to Zheng Qi and do not include Xie Qi (邪气).
2. Differentiation of “Xu” and “Shi” based on the strength of Xie Qi (邪气) and the weakness of Zheng Qi
The “Su Wen (Plain Questions) – Tong Ping Xu Shi Lun (Discussion on Xu and Shi)” states: “When Xie Qi is strong, it is “Shi”; when vital essence is depleted, it is “Xu”.”
Zhang Zhizong in the “Su Wen Ji Zhu (Commentary on Plain Questions)” explains: “Xie Qi refers to the evils of wind, cold, heat, and dampness, while vital essence refers to Ying Qi (营气) and Wei Qi (卫气). Since Xie Qi can be both weak and strong, when Xie Qi is strong, it is “Shi”; Zheng Qi can be strong or weak, hence when vital essence is depleted, it is “Xu”. Depletion means loss; it can be due to being taken by Xie Qi.”
Japanese scholar Tanba Genkan in the “Su Wen Shi (Plain Questions Commentary)” states: “When Xie Qi invades the body, it must first take advantage of the weakness of vital essence to enter. Once inside, if vital essence is abundant and Xie Qi is also strong, it is “Shi”, such as in the case of a full pattern of cold damage. If Xie Qi enters and the vital essence cannot resist it, it is taken by Xie Qi, thus it is “Xu”, as seen in the case of a direct attack pattern of cold damage.”
Whenever Xie Qi is present, whether weak or strong, it is considered a “Shi” pattern; whenever there is no Xie Qi present, it is merely a deficiency of vital essence, regardless of whether it pertains to Qi or blood, in the organs or bowels, it is considered a “Xu” pattern.
This concept is widely applied in clinical practice.
3. Differentiation of “Xu” and “Shi” based on the presence or absence of disease
There are two situations regarding the differentiation of disease and non-disease.
First, disease is considered “Shi”, while non-disease is considered “Xu”.
For example, the “Nan Jing (Classic of Difficult Issues) – Issue 48” states: “External pain and internal comfort indicate external “Shi” and internal “Xu”; internal pain and external comfort indicate internal “Shi” and external “Xu”.”
If the evil is external, there will be external pain, indicating that the evil is at the surface. For instance, in the case of Gui Zhi Tang (Cinnamon Twig Decoction) or Ma Huang Tang (Ephedra Decoction), one may only see symptoms such as aversion to cold, fever, and body aches, which are external manifestations. Since the evil has not penetrated internally, there is no discomfort internally, hence it is called external “Shi” and internal “Xu”, which is in contrast to external “Shi”; if the evil occurs internally and causes internal pain, regardless of whether it is cold or heat, it is classified as internal “Shi”; if the evil is not external, there is no discomfort externally, hence it is called external “Xu”.
Thus, “Shi” indicates disease, while “Xu” indicates non-disease, which is also a contrasting meaning.
Second, disease is considered “Xu”, while non-disease is considered “Shi”.
For example, the “Nan Jing – Issue 58” states: “Yang deficiency and Yin excess lead to sweating and recovery; purging leads to death; Yang excess and Yin deficiency lead to sweating and death; purging leads to recovery.”
Hua Shou explains: “Being affected by disease is considered “Xu”, while not being affected is considered excess. Only when it is “Xu” can the evil invade; only when it is excess can the evil not enter. This refers to the concept of exterior disease harmonizing with interior disease, particularly in the case of cold damage transmission. If the exterior disease harmonizes with the interior, sweating can be beneficial; however, if purging is applied, the exterior evil will not be eliminated, and the interior Qi will be depleted. If the interior disease harmonizes with the exterior, purging can be beneficial; however, if sweating is applied, the interior evil will not retreat, and the exterior Qi will be depleted. Therefore, it is said to lead to death, as sweating can deplete Yang, and purging can damage Yin. The terms Yin and Yang here refer to the exterior and interior aspects.”
According to Hua’s explanation, Yang deficiency indicates that Wei Qi is not sufficient externally, allowing wind and cold to invade the surface; Yin excess indicates that vital essence is abundant internally, and the organs are not diseased.
If the disease is at the surface, then sweating can help resolve it; however, if purging is applied, it will harm the uninfected Zheng Qi and cause the exterior evil to penetrate deeply into the interior, leading to death.
Yang excess indicates that Zheng Qi is abundant externally, and the surface is not diseased; Yin deficiency indicates that vital essence is deficient internally, and Xie Qi is strong in the organs. Since Xie Qi is strong in the organs, purging can lead to recovery; however, if sweating is applied, it will harm the exterior Yang, leading to both the exterior and interior being deficient, and the Xie Qi will become more solidified and unable to resolve, thus also leading to death.
Thus, this “Xu” and “Shi” are interchangeable terms for disease and non-disease, which is contrary to the meaning in the “Issue 48”.
4. Differentiation of “Xu” and “Shi” based on the severity of the disease
Generally, milder diseases are considered “Xu”, while more severe diseases are considered “Shi”.
The differentiation between the major and minor chest obstruction syndromes in the “Shang Han Lun” falls into this category.
The “Shang Han Lun” states: “In the case of cold damage for six or seven days, if there is a hard, painful mass under the heart, it is a major chest obstruction syndrome, which is treated with Da Xianxiong Tang (Major Chest Obstruction Decoction). If there is a small mass under the heart that is painful upon pressure, with a floating and slippery pulse, it is a minor chest obstruction syndrome, which is treated with Xiao Xianxiong Tang (Minor Chest Obstruction Decoction).”
The chest obstruction syndrome is classified as a Yang heat “Shi” evil that has accumulated in the chest, hence it is called “chest obstruction heat “Shi”. The more severe the heat evil and the deeper the accumulation, the more it is classified as major chest obstruction, thus treated with Da Huang (Rhubarb), Mang Xiao (Mirabilite), and Gan Sui (Kansui) to purge the heat “Shi”; if the heat evil is lighter and the accumulation is shallower, it is classified as minor chest obstruction, thus treated with Huang Lian (Coptis), Ban Xia (Pinellia), and Gua Lou (Trichosanthes) to clear the heat and disperse the accumulation.
Although there are differences in severity, they are both classified as heat “Shi” patterns.
The Xie Xin Tang (Purge the Heart Decoction) syndrome, which is a “Xu” pattern, is due to the Yang Qi of the middle jiao being deficient, with an invisible heat evil penetrating internally. Therefore, Xie Xin Tang, Sheng Jiang (Fresh Ginger) Xie Xin Tang, and Gan Cao (Licorice) Xie Xin Tang are all different treatments, but they all use Ren Shen (Ginseng), Da Zao (Jujube), Gan Jiang (Dried Ginger), and Gan Cao as the base to warm and tonify the Yang Qi of the middle jiao, supplemented with Huang Qin (Scutellaria) and Huang Lian to clear the invisible heat evil that has penetrated internally, thus the “Pi” syndrome is fundamentally a “Xu” pattern.
The “Shang Han Lun” states: “If the disease occurs in Yang and purging is applied, heat will enter and cause chest obstruction; if the disease occurs in Yin and purging is applied, it will cause “Pi”.”
Thus, the chest obstruction syndrome is referred to as “chest obstruction heat “Shi”, while the “Pi” syndrome is referred to as: “This is not heat accumulation, but due to deficiency in the stomach, causing Qi to rebel upwards, hence the hardness.” This indicates that the heat in chest obstruction is severe, thus it is a “Shi” pattern, while the mild heat in the “Pi” syndrome is classified as a “Xu” pattern.
5. Differentiation of “Xu” and “Shi” based on cold and heat
First, cold is considered “Xu”, while heat is considered “Shi”.
The “Su Wen – Tai Yin Yang Ming Lun (Discussion on the Tai Yin and Yang Ming)” states: “Yang is “Shi”, while Yin is “Xu”, which carries this meaning. Tanba Genkan in the “Yao Zhi Tong Yi (General Principles of Medicinal Treatment)” states: “Cold leading to diarrhea is widely recognized as a major deficiency that requires supplementation; tidal fever and delirium are widely recognized as a major excess that requires purging.”
The former is a “Xu” cold pattern, while the latter is a “Shi” heat pattern.
Secondly, cold is considered Yin “Shi” and Yang “Xu”, while heat is considered Yang “Shi” and Yin “Xu”.
The “Su Wen – Tiao Jing Lun (Discussion on Regulating the Menstruation)” states: “When Yin is excessive, there is internal cold; when Yang is deficient, there is external cold”; this belongs to the former; “When Yang is excessive, there is external heat; when Yin is deficient, there is internal heat”; this belongs to the latter. These all reflect the opposing nature of Yin and Yang.
6. Differentiation of “Xu” and “Shi” based on the form of the disease
This mainly involves differentiation based on the accumulation, dispersion, emptiness, and hardness of the disease.
For example, Qi stagnation upwards is “Shi”, while downward sinking is “Xu”; Qi accumulation internally is “Shi”, while external dispersion is “Xu”.
7. Differentiation of “Xu” and “Shi” based on wind evils
The “Ling Shu (Spiritual Pivot) – Nine Palaces and Eight Winds” states: “Wind that comes from its place of origin is “Shi” wind, which promotes growth and nourishes all things; wind that comes from the conflict is “Xu” wind, which harms people and causes death. One should be cautious of “Xu” wind and avoid it.”
Zhang Jiebin explains: “The place of origin refers to the place where Tai Yi resides. For example, when the moon is in the Rat position, the wind comes from the north, which is the correct winter Qi; when the moon is in the Rabbit position, the wind comes from the east, which is the correct spring Qi; when the moon is in the Horse position, the wind comes from the south, which is the correct summer Qi; when the moon is in the Rooster position, the wind comes from the west, which is the correct autumn Qi. The four corners and twelve positions all have their respective Qi.”
When the Qi is in its correct position, Zheng Qi is abundant, hence it is called “Shi” wind, which can promote growth and nourish all things. When the Qi is out of its correct position, Zheng Qi is insufficient, hence it is called “Xu” wind, which can harm people and cause death, and should be avoided.
In the “Nei Jing (Inner Canon)”, “Xu” wind and “Shi” wind are also referred to as “Xu Xie” and “Zheng Xie”. For example, the “Ling Shu – Evil Qi in the Cavity and Disease Forms” states: “Xu Xie is within the body, causing sweating and movement. Zheng Xie is within the person, causing subtle changes…”
Based on the above analysis, the concept of “Xu” and “Shi” in TCM is extensive, encompassing multiple aspects.
Within Zheng Qi, there is both “Xu” and “Shi”; within Xie Qi, there is also both “Xu” and “Shi”. Therefore, in pathological changes and patterns, there is always a presence of “Xu” and “Shi”. Simply relying on the phrase from the “Tong Ping Xu Shi Lun” that “when Xie Qi is strong, it is “Shi”; when vital essence is depleted, it is “Xu”” cannot encompass the full scope of “Xu” and “Shi”.