Dishu system

Dishu (Chinese: 嫡庶) was an important legal and moral system involving marriage and inheritance in ancient China.

In pre-modern eras, upper-class men in ancient China, Korea and Japan often had more than one spouse to ensure the birthing of a male heir to their assets and titles. In China, a priority system was created to rank the offsprings' entitlement to inheritance. Under this system, a man was allowed one official wife, called a zhengshi (正室, pronounced seishitsu in Japanese, lit. "formal household") or Di wife (嫡妻), and her son was called the Di son (嫡子). In Tang Dynasty, any man who has more than one Di wives would be considered engaging illegal marriage, liable to one year of penal labor, and the woman involved would also receive a slightly less severe punishment unless she could prove being cheated into the marriage. Either case, the marriage would be annulled.

A secondary spouse was called a ceshi (側室, lit. "side household") or Shu wife (庶妻), and her son was called the Shu son (庶子). Di sons, regardless of their age, held much higher social status than the Shu sons, and the eldest Di son (嫡長子) held overriding priority over all other children of the house. An illegitimate son, born out of wedlock, was generally categorized as a Shu son, though he would have much lower status than those born to legitimate Shu wives.

Tang dynasty law in China prescribed that if a Di son died, his eldest Di son (Di grandson) should be the successor, prioritized over all other members of the family; if a Di grandson could not be found, the Di son's next full-brother (born of the same zhengshi mother) should be the successor. If no Di offspring were available, a Shu son could be considered.

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