Mencius

A seven-book dialogic text recording the debates and travels of Mencius (c. 372-289 BC), the most important early transmitter and systematizer of Confucian thought after Confucius himself, addressed chiefly to the rulers of Qi, Liang (Wei), Song, and Teng during an age of open warfare between states competing for survival.

Its signature doctrine, xing shan, human nature is good, argues against contemporaries such as Gaozi, who held nature was morally neutral, like water that could be channeled either direction, and implicitly against the calculating universalism of Mozi. Mencius's famous thought experiment involves a child about to fall into a well: anyone who sees it, he argues, feels an involuntary pang of alarm and compassion regardless of training or self-interest, evidence of an innate moral sense, the 'four sprouts' of commiseration, shame, deference, and the sense of right and wrong, that moral cultivation completes rather than creates.

Mencius extends the claim politically: a ruler who fails to secure the people's basic livelihood forfeits Heaven's mandate to rule, and Mencius goes further than any other classical Confucian in sanctioning the deposition, even the killing, of a tyrant, arguing that a ruler who violates ren and yi is a mere fellow rather than a true sovereign and so no longer commands the loyalty owed a legitimate king. He advocated concrete policy alongside this theory, notably the well-field land distribution system and light taxation, and coined the enduring image of a cultivated 'flood-like qi,' a moral vigor built up through the patient accumulation of righteous action rather than seized all at once.

Elevated by Han Yu in the Tang and then canonized by Zhu Xi as one of the Four Books in the Song, Mencius's optimistic reading of human nature became the orthodox Confucian position against Xunzi's rival claim that human nature is bad, a disagreement that structured Confucian moral philosophy for the next two thousand years.