This essay asks why Durkheim was so opposed to free consensual unions, in a support for marriage and the family. But it is above all an attempt to explore the theoretical sources of his insistent and even dogmatic opposition to 'free unions'. Accordingly, it involves Durkheim's thinking about the sacred in two key areas. One centres round issues of filiation, and involves his account of totems, clans and the individual's social identity. The other centres round his view that individualism grows along with the increasing activity of the state, and involves interrelated questions of property, inheritance, the contract and the role of civil law. The result is a tension in his thought between an emphasis on the sacred as the origin of things and a more secular concern with the importance in modern life of moral relations expressed and regulated by civil law. Although his opposition to free unions has roots in 'children of the totem', it is suggested it is above all a modern concern with 'children of the law'.