Once again — how many times has this come up? — it is being asserted widely that the reason only mixed-sex couples can marry is that only they are “inherently” capable of procreation. This is not only false, but a fallacy.
First, though, let it be acknowledged that the state, and for what it is worth, many religions, do hold that procreation ought to take place within the context of marriage, thereby implicitly recognizing the sadly obvious fact that marriage is not essential to procreation. However, as soon as this is said, it also has to be recognized that the converse is equally true and obvious: that neither the state, nor most religions, require procreation of married couples. Some religious groups insist that couples at least attempt procreation, but the bearing of children is, for most states and most faiths, a positive outcome and not a requirement. Making the institution of marriage depend on what is essentially a contingency robs it of relation to what in fact constitutes the marriage, which is the mutual consent to life together.
In short, it is not the bearing of children that “makes” the marriage a marriage. As long ago as the 17th century, the eminent Scottish jurist James Dalrymple, the Viscount Stair, wrote in his Institutions of the Law of Scotland,
It is not the consent of Marriage as it relateth to the procreation of Children that is requisite; for it may consist, though the Woman be far beyond that date; but it is the consent, whereby ariseth that Conjugal Society, which may have the conjunction of Bodies as well as of Minds, as the general end of the Institution of Marriage, is the solace and satisfaction of Man. For the Lord saw that it was not fit for him to be alone, and therefore made a help meet for him: Yet though this capacity should never be actuat, as if persons, both capable, should after Marriage live together, and it should be known and acknowledged that they did abstain, yet were the Marriage valid, as to the Conjugal Rights on either part. (I.iv.6)
However, we then come to the fallacious belief that any given mixed-sex couple are somehow “inherently” capable of procreation, while same-sex couples never are. First of all, the obvious truth is that it takes two to dance the procreative tango — and both must be, individually as well as jointly, capable of procreation, in order for procreation to happen. The marriage of a couple consisting of one member of each sex does not have any "inherent" capacity to procreation, solely on the basis of their sex. Such a couple either has "actual" capacity for procreation or it doesn't.
So let me sketch this out in simpler terms. The “traditionalists” appear to be arguing thus:
a. Male and female are required for procreation
b. Marriage requires procreation, therefore
c. Marriage requires male and female.
I hope you can see the syllogism follows, but only if (b) is accepted as true. However, in fact its contrary is true. As it stands (b) is not acceptable to most states or faiths — any more than same-sex marriage is acceptable to most states and faiths. So those who frame the argument in this way are employing a premise they do not in fact accept to reach a conclusion they desire.
Let’s look at it another way:
a. A couple including a person of each sex, each of whom is capable of procreation has an inherent capacity to procreate as a couple.
a(1). This means that the inability of either or both members of the couple to procreate prevents the couple from procreation.
b. The inability to procreate is not grounds for forbidding marriage, or dissolving marriage.
b(1). This means that those who wish to prohibit same-sex marriage on the grounds of incapacity to procreate need to come up with a better argument.
Tobias Stanislas Haller BSG