Dishu system

The Dishu system was an important legal and moral system governing marriage and inheritance across the pre-modern Chinese cultural sphere, including China, Japan, Korea and Vietnam. It ranked a household's wives and their sons in a strict hierarchy: the one official wife, called the di wife, held paramount status, and her son, the di son, took precedence over the sons of any secondary wife, called a shu wife, regardless of the shu son's age. A man could take only one di wife at a time, though multiple shu wives were permitted, and Tang dynasty law punished bigamy involving a second di wife with a year of penal labor. A legitimate shu son still outranked any child born outside a recognized marriage. The sharp distinction between di and shu status weakened considerably after the Song dynasty. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/