The Ba Gong (The 8 categories or questions) is a way of clarifying the various symptoms and more closely aproximating the underlying syndrome. When we encounter a patient we take in all the various complaints and look for the underlying pattern. We ask ourselves is the problem:
Interior or Exterior ?
Hot or Cold ?
Excess or Deficiency ?
Yin or Yang ?
Interior and exterior is the category where the disease is located.
Exterior conditions are still on the periphery of the skin, in the muscles and channels, and interior conditions affect the organs and bones. The exterior of the body is the area where the lung defensive chi operates. For example, if you are fighting a cold and have aches in the muscles, this is an indication of an exterior pattern. The syndromes that are happening on the exterior happen quickly and resolve quickly. Disharmony that has gone to the internal organs take more time to build up, and then take longer to resolve.
Interior problems happen when the internal organs are affected. A problem may have originated from the exterior, but not dealt with properly it became a pattern of internal organs.
Cold and Hot is the second category of Ba Gong.
In a hot problem there is fever and thirst, whereas in a cold problem there are chills and sensation of coldness. Think of hot and cold in terms of next category of Ba Gong; empty and full.
Hot and cold has to do with our understanding of Yin and Yang.
In Full-Heat,the yang increases beyond normal, heats up the body and evaporates the yin. For example a man eats chili peppers, his body gets hotter and the results are that he is thirsty. To resolve this pattern one would treat the excess yang.
In Empty-Heat, yin is deficient and yang remains normal, so one would treat the yin deficiency. For example the man is working, but he has not been drinking enough water, and becomes yin deficient.
Similarly there is the full-cold, where folks are suffering from an excess of yin. Here, the man ate too much ice cream and gets a stomach pain, excess of cold.
Empty-cold is more difficult to resolve. It has happened over a longer period of time where the yang has diminished. For example, men that have too much loss of seminal fluid create a condition of tiredness and coldness. His yang is too low and must be tonified.
Full problems have a pathogenic factor and there is intact full body chi reacting to it. The Chi of the body is responding to the pathogen.
An Empty condition is where there is diminished bodily chi, and no pathogenic factor.
Yin and yang summarize the other six. For instance if it is interior, empty and cold, that is all yin. If it exterior, full and heat, this is all yang.