Along with vital force (khí or qi), one of the fundamental concepts of Neo-Confucianism during the Chinese Song dynasty.
According to Zhu Xi, universal reason is equivalent to the Tao and the first principle, the origin of everything, being and person. Reason arises from the metaphysical world, while the vital force emanates from the physical world. Imbued with universal reason from birth, every living thing is endowed with its proper nature (tính), given form (hình) by the vital force.
