Robert P. George, Sherif Girgis, and Ryan T. Anderson move toward a profound definition of marriage in their article, “The Argument Against Gay Marriage: And Why It Doesn’t Fail.”
“In making our case for conjugal marriage, we consider the nature of human embodiedness; how this makes comprehensive interpersonal union sealed in conjugal acts possible; and how such union and its intrinsic connection to children give marriage its distinctive norms of monogamy, exclusivity, and permanence.”
. . .
“marriages, being comprehensive interpersonal unions, are consummated and uniquely embodied in coitus—in acts that extend spouses’ union of hearts and minds along the biological dimension of their beings, much as various organs unite to form one body: by allowing them to coordinate together toward a biological function (in this case, reproduction) of the whole (in this case, the couple as a unit).”
. . .
“Marriage is a comprehensive union of two sexually complementary persons who seal (consummate or complete) their relationship by the generative act—by the kind of activity that is by its nature fulfilled by the conception of a child. So marriage itself is oriented to and fulfilled by the bearing, rearing, and education of children. The procreative-type act distinctively seals or completes a procreative-type union.”
The whole article is here–if you have concerns about what this means for adoption or infertility, you will find them addressed in the article.