Ancestor veneration is Confucianism's central rite and the hardest thing for outsiders to classify, since Confucius was agnostic about whether the dead hear anything. His answer was functional: sacrifice as if the spirits were present. The rites maintain the family across the boundary of death, obligate the living, and teach continuity — and the Chinese Rites Controversy of the 17th and 18th centuries, in which Rome ruled them idolatrous and cost Christianity its foothold in China, turned entirely on whether they were worship or respect.