Deficiency and excess are two principles for differentiating the states of pathogenic factors and healthy qi. Deficiency means insufficiency of healthy qi and excess means exuberance of pathogenic factors.

虚证和实证是区分邪气和正气状态的两个原则。虚指正气不足，实指邪气盛实。

The eight principles refer to yin and yang, exterior and interior, cold and heat as well as deficiency and excess. The manifestations of diseases, though complicated, can be generalized into certain patterns in the light of the eight principles.

八纲是指阴阳、表里、寒热、虚实。疾病的表现尽管及其复杂，但基本上都可以用八纲加以归纳。