The Eight Principles are one of the basic ways traditional Chinese medicine has to diagnose. It uses the following eight divisions of symptoms:

• Yin or Yang (yin-yang 陰陽)
• Superficial or internal (li-biao 表裡) gives an understanding of where the illness started, from the outside or from the inside. Also can give an indication of the direction the illness is taking, becoming more external or going deeper into the body.
• Cold or hot (han-re 寒熱)
• Deficient or Replete (xu-shi 虛實)