We come now to the essay in The Meaning of Marriage of Robert George, co-editor of the book and one of the heavy hitters of Catholic natural law thinking today.
His argument is that men and women are complementary.
Marriage is a unitive act – an act that unites these two complementary persons, making two people into one flesh.
Marriage is a human good even if children do not result, but the act of marriage aims at procreation.
SO acts which unite people who are not complementary types and which could not be procreative are not marriages, whatever else they might be.
George, and Catholic natural law thinkers in general, would make an argument like this even if alternative theories of marriage were not on the table. Since, however, arguments for homosexual marriage are at issue now, he has to argue for an understanding of marriage that includes sterile men and women, but excludes same-sex couples.
The key claim for including sterile couples is that the marital act is "reproductive in type," even though "some other conditions in the agents may prevent procreation from occurring."
The key claim for excluding same-sex couples is that men and women are complementary types of persons, in a way that two men or two women are not.
I strongly believe that men and women as types of persons are designed to be complementary (those of delicate Darwinian sensibilities may substitute "have evolved" for "are designed").
I very much like the formulation that marriage makes two persons one flesh, and that the law does not make people married, but can only recognize one-flesh unions which have been made by other hands.
I do think that the aim, point, intent, designed purpose, and telos of marriage is children. Couples who cannot have children, but are open to them, are really married.
The place at which my Calvinist understanding balks is at the phrase "acts which are reproductive in type." This seems to me to be, to use an old Prot insult, Jesuitical casuistry – a too-neat distinction designed to get to a pre-ordained conclusion.
BUT I don't know what the right alternative is.
I have not written much about same-sex marriage, the issue of the day, because I am stuck on this point.
I would welcome your edifying responses.