Abstract: Since the late Qing Dynasty, the scope of prohibited marriage in China's marriage law has undergone a change from wufu (five grades of mourning) to sandai(three generations). Since the Zhou Dynasty, traditional Chinese society had adhered to the Zhou etiquette of "no marriage between members of the same clan". Marriage between cousins(except paternal parallel cousins) had been left to the discretion of the family and not prohibited by law. In 1930, in accordance with the principle of equality between men and women, the kinship section of the Republic of China Civil Code changed the classification of traditional Chinese kinships of internal relatives and extermal relatives to Western-style blood relatives and in-laws, thus introduced a problem of whether or not clan members outside of the wufu circle and cousins within three generations could marry each other. This paper points out these contradictions and conflicts by examining the contradiction between the principle of freedom of marriage under the 1950 Marriage Law and the common practice of "no marriage between members of the same clan", and the conflict between eugenic policy and freedom of marriage in the 1980 Marriage Law. The root of these contradictions is the fact that Chinese kinship and Western kingship classifications are incompatible. Chinese kinship categorization is based on the social "clan surnames" system rather than the biological "sex" system, and the traditional social practice of no marriage within the same clan and marriage between cousins (except paternal parallel cousins) is due to the kinship system's emphasis on internal relations over external ones rather than on male over female preference. Nowadays, with the abolition of change of surnames for women after marriage, the traditionally external (e.g. maternal) relatives can now be regarded as internal relatives, the "no marriage within the same clan" can be applied to both clans. The eugenic reason for prohibiting marriage of collateral relatives within three generations and the etiquette reason for the no-marriage within the same clans can go hand in hand now because eugenics serves the continuation of the clan.

Key words: internal relatives, external relatives, blood relatives, cousin marriage