The wufu is a scale, and what it measures is closeness of kin. Five grades of mourning dress, running from the coarsest cloth to the finest and from the longest term to the shortest, were assigned to every relationship a person could stand in to a dead relative. A son mourning a father wore zhancui, sackcloth so plainly made that its edges were left untrimmed, and kept the mourning for what was called three years. A man mourning a distant cousin wore sima, fine hemp, for three months. In between came three intermediate grades, each with its own cloth, its own term and its own list of relatives.
The system is not a description of feeling. It is a prescription, and the tradition was explicit that the outward form was there to give grief a shape it could be carried in and then set down. Wearing the cloth carried obligations with it: withdrawal from office, abstention from meat and wine, from music and from marriage, and in the heaviest grade a simple hut and a plain diet.
The grades also worked outward from the dead person in both directions, so that the chart was symmetrical and complete. Everyone in a Chinese descent group could find their own square on it. That is what made the wufu useful for purposes far from the funeral itself: it was the one place where the boundary of a family was written down in a way that admitted no argument, and both the state and the lineage used it as such.