‘Xu’ (虚) and ‘Shi’ (实) refer to the nature of pathological changes and are extremely important in differential diagnosis.
Therefore, ‘Xu’ indicates the need for tonification, while ‘Shi’ indicates the need for purging, which are essential methods for diagnosis and treatment; tonification leads to ‘Shi’, while purging leads to ‘Xu’, which are the inevitable results of accurate diagnosis and treatment. However, understanding the ‘Xu’ and ‘Shi’ of pathological changes and the corresponding treatment methods can be quite challenging. To aid in research and provide references for differential diagnosis and treatment, I have compiled the meanings of ‘Xu’ and ‘Shi’ based on literature and clinical experience.
When analyzing the ‘Xu’ and ‘Shi’ of pathological changes during differential diagnosis, it has various meanings that should not be confused, as this would affect the accuracy of the diagnosis. Upon detailed analysis, there are approximately the following meanings:
1. Differentiating ‘Xu’ and ‘Shi’ based on the strength of Zheng Qi (正气)
According to the “Shang Han Lun (伤寒论) – Ping Mai Fa (平脉法)”, 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 (辨平脉章句)” that: “The terms ‘coming’ and ‘leaving’ refer to the pulse’s entry and exit; entry and exit pertain to the internal and external aspects of Yin, Yang, blood, and Qi. A quick entry and slow exit indicate more Qi is exiting than entering, thus ‘external Shi’; a slow entry and quick exit indicate more Qi is entering than exiting, thus ‘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. Differentiating ‘Xu’ and ‘Shi’ based on the strength of Xie Qi (邪气) and the weakness of Zheng Qi
The “Suwen (素问) – Tong Ping Xu Shi Lun (通评虚实论)” states: “When Xie Qi is strong, it is ‘Shi’; when vital essence is depleted, it is ‘Xu’.”
Zhang Zhizong in the “Suwen Jizhu (素问集注)” 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 either weak or strong, when Xie Qi is strong, it is ‘Shi’; Zheng Qi can be either strong or weak, hence when it is depleted, it is ‘Xu’. ‘Depletion’ means loss, which can be due to Xie Qi’s invasion.”
Japanese scholar Tanba Genkan in the “Suwen Shi (素问识)” states: “When Xie Qi invades the body, it must first take advantage of the weakness of vital essence to enter. If it enters and vital essence is strong, both will be strong, resulting in ‘Shi’, as seen in the case of ‘Shang Han Wei Jia Shi Zheng’. If Xie Qi enters and vital essence cannot resist it, it is taken by Xie Qi, resulting in ‘Xu’, as seen in the case of ‘Shang Han Zhi Zhong Zheng’.”
Whenever Xie Qi is present, regardless of its strength, it is considered a ‘Shi’ condition; 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’ condition.
This concept is widely applied in clinical practice.
3. Differentiating ‘Xu’ and ‘Shi’ based on the presence or absence of disease
There are two situations regarding the differentiation of ‘Xu’ and ‘Shi’ based on disease presence.
First, considering disease as ‘Shi’ and absence of disease as ‘Xu’
As stated in the “Nanjing (难经) – Si Shi Ba Nan (四十八难)”: “External pain and internal comfort indicate ‘external Shi’ and ‘internal Xu’; internal pain and external comfort indicate ‘internal Shi’ and ‘external Xu’.”
When Xie Qi invades externally, it causes external pain, indicating that the Xie Qi is on the surface. For example, in cases of Gui Zhi Tang (桂枝汤) and Ma Huang Tang (麻黄汤), one may only see symptoms like aversion to cold, fever, and body aches, which are external manifestations. Since the Xie Qi has not penetrated internally, the internal aspect is comfortable and without suffering.
Thus, when the disease is external, it is termed ‘external Shi’, and when there is no internal suffering, it is termed ‘internal Xu’, which is in contrast to ‘external Shi’;
When the disease occurs internally and causes pain, regardless of whether it is cold or heat, it is classified as ‘internal Shi’ based on the location of the disease; since the disease is not external, there is no external suffering, hence it is termed ‘external Xu’.
Thus, ‘Shi’ indicates disease, while ‘Xu’ indicates absence of disease, which is also a contrasting meaning.
Second, considering disease as ‘Xu’ and absence of disease as ‘Shi’
As stated in the “Nanjing – Wu Shi Ba Nan (五十八难)”: “Yang Xu and Yin Sheng, sweating leads to recovery; purging leads to death; Yang Sheng and Yin Xu, sweating leads to death; purging leads to recovery.”
Hua Shou explains: “When the disease is ‘Xu’, the non-disease is ‘Sheng’. Only when it is ‘Xu’ can the Xie Qi invade; only when it is ‘Sheng’ can the Xie Qi not enter. This refers to the concept of ‘exterior disease and interior harmony’ and ‘interior disease and exterior harmony’, particularly in cases of Shang Han transmission. When there is exterior disease and harmony, sweating can be used to resolve the exterior; if purging is used, it harms the un-diseased Zheng Qi and causes the exterior Xie Qi to penetrate deeply into the interior, leading to death. When the disease is internal, purging can be used to resolve it; if sweating is used, the internal Xie Qi does not retreat, and the exterior Qi is also depleted, leading to death.”
Thus, this ‘Xu’ and ‘Shi’ are interchangeable terms for disease and non-disease, which is contrary to the meaning in the “Si Shi Ba Nan”.
4. Differentiating ‘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 forms of Xian Xiong Tang (大小陷胸汤) and Xie Xin Tang (泻心汤) in the “Shang Han Lun” belongs to this category.
In the “Shang Han Lun”, it states: “In cases of Shang Han for six or seven days, if there is a hard, painful mass under the heart, with a deep and tight pulse, it is a case for Da Xian Xiong Tang (大陷胸汤); if there is a small mass under the heart, with a floating and slippery pulse, it is a case for Xiao Xian Xiong Tang (小陷胸汤).”
The Xian Xiong condition generally belongs to the category of Yang heat and ‘Shi’ evil accumulating in the chest, hence it is called ‘Xian Xiong Re Shi’.
If the heat evil is strong and deeply accumulated, it is classified as ‘Da Xian Xiong’, hence the use of Da Huang (大黄), Mang Xiao (芒硝), and Gan Sui (甘遂) to purge the heat and ‘Shi’; if the heat evil is mild and shallow, it is classified as ‘Xiao Xian Xiong’, hence the use of Huang Lian (黄连), Ban Xia (半夏), and Gua Lou Shi (瓜蒌实) to clear heat and disperse the accumulation.
Although there are differences in severity, they are both classified as ‘Shi’ due to the presence of heat.
The Xie Xin Tang condition, which is a ‘Xu’ condition, is due to the prior deficiency of Yang Qi in the middle burner, leading to the internal invasion of formless heat evil. Therefore, the various forms of Xie Xin Tang, such as Ban Xia Xie Xin Tang (半夏泻心汤), Sheng Jiang Xie Xin Tang (生姜泻心汤), and Gan Cao Xie Xin Tang (甘草泻心汤), all differ in their treatment but are based on the use of Ren Shen (人参), Da Zao (大枣), Gan Jiang (干姜), and Gan Cao (甘草) to warm and tonify the Yang Qi of the middle burner, supplemented with Huang Qin (黄芩) and Huang Lian (黄连) to clear the formless heat evil that has invaded internally, thus the ‘Pi’ condition is fundamentally a ‘Xu’ condition.
The “Shang Han Lun” states: “If the disease occurs in Yang and purging is used, heat will enter and cause Xian Xiong; if the disease occurs in Yin and purging is used, it will cause ‘Pi’.”
Thus, the Xian Xiong condition is termed ‘Xian Xiong Re Shi’, while the ‘Pi’ condition is termed: “This is not due to heat, but due to the deficiency of the stomach, causing Qi to rise and become hard,” indicating that the heat in Xian Xiong is severe, hence it is a ‘Shi’ condition, while the mild heat in the ‘Pi’ condition is classified as a ‘Xu’ condition.
5. Differentiating ‘Xu’ and ‘Shi’ based on cold and heat
First, cold is considered ‘Xu’, while heat is considered ‘Shi’.
The “Suwen – Tai Yin Yang Ming Lun (太阴阳明论)” states: “Yang is ‘Shi’, while Yin is ‘Xu’,” which carries this meaning. Tanba Genkan in the “Yao Zhi Tong Yi (药治通义)” states: “Cold leading to diarrhea is widely recognized as a major deficiency that requires tonification; tidal fever and delirium are widely recognized as major excess that requires purging.”
The former represents a ‘Xu’ cold condition, while the latter represents a ‘Shi’ heat condition.
Secondly, cold can be considered Yin ‘Shi’ and Yang ‘Xu’, while heat can be considered Yang ‘Shi’ and Yin ‘Xu’.
The “Suwen – Tiao Jing Lun (调经论)” states: “When Yin is strong, it leads to internal cold; when Yang is weak, it leads to external cold;” this belongs to the former; “When Yang is strong, it leads to external heat; when Yin is weak, it leads to internal heat;” this belongs to the latter. These are all oppositional concepts of Yin and Yang, each corresponding to its category.
6. Differentiating ‘Xu’ and ‘Shi’ based on the form of the disease
This primarily 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. Differentiating ‘Xu’ and ‘Shi’ based on the location of wind evil
The “Ling Shu (灵枢) – Jiu Gong Ba Feng Pian (九宫八风篇)” states: “Wind that comes from its native place is ‘Shi’ wind, which promotes growth and nourishes all things; wind that comes from the opposing direction is ‘Xu’ wind, which harms people and is deadly. One should be cautious of ‘Xu’ wind and avoid it.”
Zhang Jiebin explains: “The native place refers to the place where Tai Yi resides. For example, when the moon is in the ‘Zi’ position, the wind comes from the north, representing the correct winter Qi; when the moon is in the ‘Mao’ position, the wind comes from the east, representing the correct spring Qi; when the moon is in the ‘Wu’ position, the wind comes from the south, representing the correct summer Qi; when the moon is in the ‘You’ position, the wind comes from the west, representing the correct autumn Qi. The four corners and twelve positions all have this principle.”
When Qi is in its correct position, Zheng Qi is abundant, hence it is termed ‘Shi’ wind, which can promote growth and nourish all things. When Qi is out of its correct position, Zheng Qi is insufficient, hence it is termed ‘Xu’ wind, which can harm people and is deadly, and should be avoided.”
‘Xu’ wind and ‘Shi’ wind are also referred to as ‘Xu Xie’ and ‘Zheng Xie’ in the “Neijing (内经)”. For example, the “Ling Shu – Xie Qi Cang Fu Bing Xing Pian (邪气藏府病形篇)” 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 Traditional Chinese Medicine is extensive and encompasses multiple aspects.
Both Zheng Qi and Xie Qi can be ‘Xu’ or ‘Shi’, thus in pathological changes and conditions, 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’.
Note: This article was published in the “Selected Lectures on Traditional Chinese Medicine, Volume 1”
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