Li is ritual, rite, propriety, ceremony, the whole body of prescribed form governing conduct, from state sacrifice and court ceremonial to mourning, marriage, and the ordinary courtesies of greeting, seating and eating. In Confucian thought it is a central category, and the Analects treat it as inseparable from inner disposition: ritual without humaneness is worthless, and Confucius asks what a man who lacks humaneness has to do with ritual at all.
The tradition's claim about li is psychological as much as social. Prescribed form is held to shape the person who performs it, so that acting correctly cultivates the corresponding disposition rather than merely expressing one already present. That reasoning lies behind the Confucian emphasis on practice, comportment and detail, and behind the fact that the Analects describe Confucius as much through how he sat, ate, dressed and entered a room as through what he said. Li also distinguishes: it marks relations, roles and occasions, and by doing so makes social life legible to those in it.
The great internal dispute concerns the relation of li to human nature. Mencius held that human nature is good and that ritual develops what is already there, the four sprouts, of which the sense of deference is one. Xunzi held that human nature is bad, or at any rate unruly, and that ritual is a deliberate invention of the sage-kings for shaping desire into order; on his account ritual does not express nature but corrects it, and his essay on ritual is classical China's most sustained treatment of the subject. Both positions were transmitted. Mencius' became orthodox in the Neo-Confucian tradition, and Xunzi's account of ritual as a human construction has drawn increasing attention in modern scholarship, including from philosophers interested in what it shares with contemporary accounts of social norms.
The critics were sharper still. Mozi attacked elaborate funerals and ceremonial music as wasteful. The Daoist texts treated li as a symptom of decline, the Daodejing places it last in a sequence in which the Dao, then de, then humaneness, then righteousness have each been lost in turn, and calls it the thin husk of loyalty and the beginning of disorder. The Legalists held that law and punishment, not ritual, produce compliance, and said so in explicit opposition. Neo-Confucianism later gave li a metaphysical setting by connecting it to the homophone li meaning principle or pattern, a different word, written differently, but the connection was drawn deliberately in Song thought and did a great deal of work there.