In Mencius’ theory of the original goodness in human nature, fate is the original source of xing (nature). Heart is the appearance of nature. There are two aspects to nature and heart: ti (form) and yong (function). From the perspective of form, nature is liangzhi (the goodness in conscience) and liangneng (the inborn ability to be good) in human beings and heart is human’s conscience and original heart. From the perspective of function, nature is the four things of benevolence, righteousness, propriety and wisdom, and heart consists in compassion, shame, respect, right and wrong. As the foundation for the theory of the original goodness in human nature, conscience and heart are a combination of human moral instinct, moral rationality and moral volition, whereas moral instinct gradually rises to moral volition and passes through moral rationality. Mencius’ theory of the original goodness in human nature is not a theory of future goodness, but a theory of original goodness.