St Thomas's hylomorphic anthropology grounds his famous statement of the precepts of the natural law in the Summa Theologiae. When we come to the third precept of the natural law, namely man's inclination to good according to the nature of his reason, we enter into the realm of politics. On account of the incarnate nature of human reason, the other natural human inclinations are also imbued with political significance. Right reason, which is also incarnate reason, tells us that procreation and marriage have an intrinsic mutual ordination to each other. Heterosexual marriage is the unique locus in which children can both be procreated and be given the upbringing and education which is their right. Since society has a special purchase on children in order to ensure its future – and its future well-being – heterosexual marriage ought to enjoy a special legal status and protection. The corollary is that society can only undermine the conditions of its own well-being if it tries to tamper with the meaning of marriage as heretofore understood by granting gay unions the legal rights and duties of heterosexual marriage.