Zhu Xi held that li, together with qi (氣: vital, material force), depend on each other to create structures of nature and matter.
Zhu Xi maintained, however, that his notion is found in the I Ching (Book of Changes), a classic source of Chinese philosophy.
Wang Yangming, a philosopher who opposed Zhu Xi's ideas, held that li was to be found not in the world but within oneself.
However, in the practice of Traditional Chinese medicine, the endogenous and exogenous interpretations of these two philosophical ideas are not seen as mutually exclusive but are viewed, to create and control each other.
The Huangdi Neijing (Chinese: 黃帝內經; pinyin: Huángdì Nèijīng), meaning the Inner Canon of the Yellow Emperor, is the most important ancient text for the study of Medical and Daoist theory and lifestyle.