Relative predomination and decline of yin and yang refer to the changes of yin and yang beyond the normal range due to various factors. Relative predomination and decline of yin and yang directly cause excess syndrome and deficiency syndrome. Relative predomination of yin and yang leads to excess syndrome while relative decline of yin and yang leads to deficiency syndrome. Predomination and decline of yin and yang also decide the nature of disease. Relative predomination of yang and deficiency of yin cause heat syndrome while domination of yin and deficiency of yang bring on cold syndromes.

When yin or yang becomes predominant, it becomes a pathogenic factor and causes excess syndrome because "excess of pathogenic factors leads to excess syndrome".

When yin becomes predominant, it will bring on cold syndromes; when yang becomes predominant, it will lead to heat syndromes.

Relative predomination of yang refers to excess-heat syndrome marked by predomination of yang and non-deficiency of yin due to relative predomination of yang-qi and hyperactivity of body functions during the course of disease. It results either from imbalance between yin and yang, or from attack of exogenous warm pathogenic factors, or from attack of pathogenic factors of yin nature that transforms into heat with yang, or from endogenous impairment due to abnormal changes of emotions and heat transformed from abnormal changes of emotions, or from heat transformed from qi stagnation, blood stasis, phlegm and retention of food that make yang-qi predominant. 

Predomination of yang leads to heat, so usual clinical manifestation is fever, accompanied by profuse sweating, thirst, reddish complexion, reddish tongue with yellowish coating, full and large or rapid pulse; or accompanied by pathogenic heat disturbing the interior with the symptoms of dysphoria, insomnia, mania, dry feces and scanty brownish urine, etc.

Predomination of yang impairs yin. So predomination of yang is usually characterized by consumption of yin-fluid. At the medium and advanced stages of disease, pathogenic yang gradually declines and the consumption of yin-fluid is more and more serious, eventually leading to yin-deficiency syndromes.

      

Relative predomination of yin refers to excess-cold syndrome marked by relative predomination of yin-qi, decline of body functions and retention of pathological substances in the course of disease. It may result either from attack of pathogenic cold and dampness, or from excessive intake of cold and uncooked food that makes yin-qi in the body predominant. Predomination of yin generates cold and obstructs yang-qi, clinically leading to cold symptoms, such as chills, dispiritedness, pale complexion, anhidrosis, preference for hot water, cold limbs, loose stool, clear urine, whitish tongue coating, deep and slow pulse, etc.

      

Since predomination of yin leads to disorder of yang, relative predomination of yin obstructs or impairs yang. At the medium and advanced stages of disease, pathogenic yin gradually declines and yang-qi becomes more and more deficient, eventually bringing on yang-deficiency syndromes.

Normally both yin and yang pertain to healthy qi in the body. Once yin or yang declines, insufficiency of healthy qi will be caused. So both relative decline of yin and yang can lead to deficiency syndrome because "loss of essence causes deficiency". Usually relative decline of yin brings on deficiency-heat syndrome while relative decline of yang results in deficiency-cold syndrome.

Relative decline of yang results either from imbalance between yin and yang and excessive consumption of yang-qi, or from congenital weakness and insufficiency of fire in life-gate, or from improper postnatal care and impairment of yang-qi, or from impairment of yang-qi during the course of disease. Deficiency of yang-qi generates cold and clinically brings on deficiency-cold syndrome and decline or weakness of viscera functions, leading to the symptoms of aversion to cold, cold limbs, mental lassitude, poor appetite, loose stool, clear and profuse urine, and deep-slow-weak pulse, etc.

Yang-deficiency syndrome mainly involves the spleen and the kidney, mainly characterized by deficiency of kidney-yang. Since kidney-yang is the foundation of yang-qi in the other organs, deficiency of kidney-yang will make spleen-yang insufficient. Since the spleen is the acquired base of life, deficiency of spleen-yang weakens the functions of transportation and transformation, eventually leading to insufficient production of blood and qi and aggravating the state of yang deficiency.

Deficiency of yang makes it difficult to restrict yin, leading to interior exuberance of yin-cold or retention of water-dampness or interior blockage of blood stasis which may further stagnate qi activity and bring on serious dysfunction of the viscera.

Relative decline of yin may result either from imbalance between yin and yang and excessive consumption of yin-essence, or from congenital weakness and insufficiency of yin-fluid, or from improper postnatal care and exhaustion of yin-fluid, or from insufficiency of yin-fluid in the course of disease. Deficiency of yin generates heat and clinically brings on deficiency-heat syndrome and various hyperactivities of viscera functions, leading to the symptoms of emaciation, low fever, feverish sensation in the five centers (palms, soles and chest), night sweating, dry mouth, dry feces, scanty urine, reddish tongue coating or no tongue coating, thin and rapid pulse, etc.

Deficiency of yin mainly involves the liver and the kidney, mainly marked by kidney-deficiency. Since kidney-yin is the foundation of yin in the other viscera, deficiency of kidney-yin makes liver-yin insufficient.

Deficiency of yin cannot restrict yang and brings on endogenous heat and fire with the symptoms of irascibility and insomnia, etc. Insufficiency of liver-yin makes liver-yang hyperactive. Hyperactivity of liver-yang transforms into fire that disturbs the upper orifices and leads to dizziness, headache or even apoplexy and syncope, etc.