Confucius, in his era, proclaims that every person should awake and treat himself in sincere way. In so doing, he will perceive a dynamism from within to urge himself to do good things. Confucius' core idea is "ren", the meaning of which covers the nature, the correct way, and the fulfillment of human beings. A person, being sincere, will assure that his nature is tending toward goodness, that his correct way is choosing what is good and holding it fast, and his fulfillment is attaining perfection like a sage. Later on, Mencius develops and completes Confucius' system which can be adequately described as the theory of human nature as tending toward goodness.