In the eight principles, external and internal, cold and heat as well as asthenia and sthenia generalize the nature of diseases from the aspects of the location and nature of diseases as well as the conditions of the healthy qi and pathogenic factors. However, different aspects of the nature of diseases are inter-related. For example, cold and heat nature of diseases as well as the predominant and deficient states of healthy qi and pathogenic factors cannot exist independent of the external or internal location of diseases; accordingly, external syndrome or internal syndrome cannot exists independent of cold and heat as well as?asthenia and sthenia nature of diseases. The inter-relation between the internal and external, cold and heat as well as asthenia and sthenia may bring about various syndromes. The following is a brief discussion of the major ones.

External cold syndrome  
External cold syndrome refers to the symptoms of exogenous disease at the primary stage caused by pathogenic wind and cold attacking the surface of the body.

Clinical manifestations:
Severe aversion to cold, light fever, pain of head and body, stuffy and running nose, no sweating, whitish thin and moist tongue fur, floating and tense pulse.

Analysis of symptoms:
Aversion to cold is due to pathogenic cold attacking the superficies and stagnating rang in the superficies; fever is due to healthy qi fighting against pathogenic factors; pain of head and body is due to pathogenic cold stagnating the meridians and preventing meridian qi from free flowing; stuffy and running nose is due to failure of the lung to disperse; no sweating is due to obstruction of the muscular interstices by cold which tends to contract; whitish thin and moist tongue fur as well as floating and tense pulse are signs of pathogenic cold encumbering the surface of the body.


External heat syndrome  
External heat syndrome refers to symptoms of exogenous febrile disease at the primary stage caused by wind and heat attacking the surface of the body.

Clinical manifestations:
Fever, slight aversion to wind and cold, headache, or sweating, slight thirst, swelling sore-throat, red margin and tip of tongue, whitish thin tongue fur or yellowish thin and dry tongue fur, floating and fast pulse.

Analysis of symptoms:
Slight aversion to cold and fever are due to wind and heat attacking the surface of the body and the fact that heat is a pathogenic factor of yang nature; headache and swelling sore-throat are due to upper disturbance by pathogenic heat; sweating is due to upper floating of pathogenic heat that loosens the muscular interstices; slight thirst is due to mild impairment of body fluid by pathogenic heat; red margin and tip of tongue as well as floating and fast pulse are signs of wind and heat attacking the surface of the body.

External sthenic syndrome  
External sthenic syndrome refers to symptoms of exogenous disease at the primary stage caused by pathogenic cold attacking the surface of the body. This syndrome is marked by severe aversion to cold, no sweating and floating and tense pulse, also known as external sthenic syndrome of cold attack which is discussed in the section of external cold syndrome.

External asthenia syndrome
External asthenia syndrome usually refers to two kinds of syndromes. One is the external syndrome caused by exogenous wind attack and marked by aversion to wind, spontaneous sweating and floating and moderate pulse. This syndrome is called exogenous external asthenia syndrome as compared with external sthenia syndrome of cold attack marked by severe aversion to cold, no sweating and floating-tense pulse. The other is external asthenia syndrome of internal impairment caused by looseness of weiqi resulting from asthenia of pulmonary and splenic qi
 
Clinical manifestations:
Light fever, aversion to wind, headache, sweating, whitish thin tongue fur, floating and moderate pulse, or frequent spontaneous sweating, susceptibility to common cold, accompanied by pale complexion, lassitude, shortness of breath, asthma right after movement, poor appetite, loose stool, pale tongue with white fur and thin and weak pulse.

Analysis of symptoms:
Fever, sweating and aversion to cold seen in exogenous external asthenia syndrome are due to disharmony between weiqi and yingqi and looseness of muscular interstices resulting from pathogenic invasion of the surface of the body by wind which tends to open and outburst; headache is due to wind attacking the superficies and inhibited flow of meridian qi; whitish thin tongue fur and floating and moderate pulse are signs of pathogenic wind lingering in the superficies. In external asthenia syndrome of internal impairment, frequent spontaneous sweating and susceptibility to common cold are due to looseness of muscular interstices and weakness of weiqi and yingqi due to qi asthenia in the lung and the spleen.

The lung governs qi and manages respiration; while the spleen governs transformation and transportation; both of which are the production source of qi and blood. Asthenia of pulmonary and splenic qi and hypofunction of the lung and the spleen lead to such symptoms like pale complexion, lassitude, shortness of breath, asthma right after movement, poor appetite, loose of stool, pale tongue with white fur as well as thin and weak pulse, etc.