The cultural institution of conjugal monogamy, understood as the committed union of one man and one woman, has long performed a valuable task for civil society. It connects parenting to procreation, securing both normative and practical links between children and their parents—fathers in particular. Until recently, the legal institution of marriage—the institution created by law that we call “marriage”—has always mapped directly over the cultural institution of conjugal monogamy. (Consider, for example, the legal presumption of paternity that attaches to husbands.) Thus the state encouraged the cultural institution in its important work, work that the state is on its own ill-equipped to perform. By singling out for special treatment the one relational arrangement that is capable of producing children, the law created normative and practical incentives for parents, especially fathers, to care for the children that they produced. And this was long understood to be a good thing.

Recently, two judges of the United States Court of Appeals for the Ninth Circuit became the latest in a line of narrow judicial majorities to decide that the legal institution of marriage serves society better by directing the state’s approbation toward homosexual intimacy than by connecting parenting with procreation. Like the high courts of Massachusetts, Connecticut, California, and Iowa, the Ninth Circuit panel ruled that the conjugality predicate must be struck from a state’s definition of marriage. A few other judicial decisions have reached the same result. But the progression of reasoning in these cases in particular reveals a trend that ought to concern everyone, even those who favor the result.

One of the primary functions of a judicial opinion is to explain how the court reached its holding. It is, in other words, to demonstrate that the court’s holding is not arbitrary but rather grounded in reason. The legitimacy of the judiciary rests entirely upon the authority of judicial reasoning. Courts have no armies or police forces. They command obedience only insofar as they provide reasons to obey. If judges command what they happen to prefer, rather than what in reason the law requires, then their decisions are merely personal opinions. In our democratic republic no mere opinion is vested with any more authority than any other.

Consider in this light the fact that the five prominent appellate courts listed above followed four different lines of reasoning; only the Iowa court followed a previous court’s rationale. The lack of consistency is striking. That the courts took such radically different routes to the same result suggests that it was the result that drove the reasoning. And this should concern not only proponents of conjugal marriage but also everyone who cares about the rule of law.

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In late 2003 and early 2004 the Massachusetts Supreme Judicial Court issued a pair of landmark decisions on marriage. In its first decision, Goodridge v. Department of Public Health, a one-vote majority of the court declared that the conjugal definition of marriage violated the state constitution. In its second decision, Opinions of the Justices to the Senate, the court ruled that extending all of the rights and privileges of marriage to same-sex couples—but not the name “marriage” itself—would not be sufficient to cure the constitutional defect. Only by declaring in law that same-sex relationships are the same as conjugal relationships could the state satisfy the demands of equal protection. (The court thus helpfully demonstrated that the creation of same-sex marriage is not about equal rights, and is not a morally neutral project). The court conceded that procreation is an “unbridgeable difference between same-sex and opposite-sex couples.” But the majority nevertheless insisted that the link between marriage and procreation is not a rational basis for conjugal marriage laws. The court found no suspect or quasi-suspect classifications involved, and declared no new-found fundamental rights. It simply ruled that conjugal marriage is irrational.

In May 2008 a simple majority of the California Supreme Court struck down a statutory scheme that retained the historical, conjugal definition of marriage and opened to same-sex couples a new institution, the domestic partnership, with all of the rights and benefits of marriage. Apparently not willing to declare the institution of conjugal marriage irrational, as the Massachusetts high court had done, the California Supreme Court took a different route. Observing that the term “marriage” is “unreservedly approved and favored by the community,” the court found in the California constitution a fundamental right to have the relationship of one’s choice called “marriage.” Inexplicably, the court seemed to assume that this right extended only to same-sex relationships, not to other relationships for which California citizens might seek the state’s approval, such as polygamy.

In October 2008 a one-vote majority of the Connecticut Supreme Court also struck down a statutory scheme extending to same-sex couples the rights and privileges of marriage, but reserving for conjugal couples the term “marriage.” The Connecticut court followed the reasoning of neither the Massachusetts court nor the California court. It blazed yet another trail to the same destination, declaring homosexuality a quasi-suspect classification for equal protection purposes. On that ground it extended special legal protection to same-sex couples. At the heart of the court’s finding was the argument that homosexuals create their personalities and identities by freely engaging in intimate conduct, and that therefore homosexuality is an immutable characteristic, on the basis of which homosexuals are vulnerable to arbitrary discrimination. Students of elementary logic will note that the court’s premise directly contradicts the conclusion deduced from it. But building on its non sequitur, the court nevertheless concluded that conjugal marriage laws burden the quasi-suspect class of homosexuals without a sufficiently important reason. The Iowa Supreme Court followed this same path when it created same-sex marriage in 2009.

A cautious judge might hesitate to declare irrational an institution on which countless societies have depended for their survival and flourishing, as the Massachusetts high court did. He might be reticent to discover, as the California court found in its state constitution, a fundamental right to have the relationship of one’s choice called “marriage.” And he might be eager to avoid the logical fallacies at the hearts of the Connecticut and Iowa decisions; one cannot be perceived as reasonable if one is not at least logical. A circumspect judge might therefore avoid the pitfalls and follies altogether, and might observe that conjugal monogamy is sui generis, a relationship intrinsically different from all other relationships. On the basis of that observation he might conclude that, whatever legal recognition states might or might not extend to same-sex relationships, it is rational—indeed, it is important—for states to distinguish conjugal marriage from every other type of arrangement. Friendships, business partnerships, tennis pairs, union organizations, and even same-sex couplings might have plausible claims to some form of legal recognition in law, but it is perfectly reasonable for the state to decline to call those relationships marriages. In other words, a judge who is concerned that his opinions be viewed as reasoned might decide the case based upon reason and upon law.

Judge Reinhardt is not a cautious judge. Writing an opinion for a two-judge majority of the Ninth Circuit last month, Judge Reinhardt carved a fourth path to legal recognition of same-sex marriage. Because the California Supreme Court struck down the state’s conjugal marriage law, when the people of California reinstated the privilege for conjugal marriage via Proposition 8 they stripped same-sex couples of an “important right,” namely the “right to obtain and use the designation of ‘marriage’ to describe their relationships.” Because California briefly allowed same-sex couples to use the term “marriage” it could not withdraw the designation, “while leaving in place all of its incidents.” Though he purported to resolve the case on “narrow grounds,” Judge Reinhardt actually concocted a wholly new justification for striking the conjugality predicate from law.

As Matthew Franck pointed out in Public Discourse, Judge Reinhardt’s decision rests upon an elision. In order to make the case appear as if it came within existing U.S. Supreme Court precedent, Judge Reinhardt treated the pronouncement of a simple majority of the judges of the California Supreme Court as if it were the state constitution itself. On Reinhardt’s logic, the California court’s decision, which Proposition 8 overruled, rendered Proposition 8 unconstitutional. Reinhardt thus reads the U.S. Constitution to prevent citizens from overruling state supreme court decisions that they believe are errant. This is a novel theory indeed.

As one supporter of same-sex marriage has observed, Reinhardt’s argument is dishonest. Indeed, Judge Reinhardt’s decision has earned criticism even from those who support the result he reached. It is not difficult to see why. Supporters of same-sex marriage are not content with mere rulings in their favor. They understandably want to see courts make principled rulings in their favor. (It is interesting to note in passing that scholars who hope for legal recognition of same-sex marriage also cannot agree on any principled ground for that position. If the case for same-sex marriage is inexorably entailed in some provision of law, then one would expect it to appear obvious to those who are most inclined to find it persuasive.)

No one should want to see the judicial branch sacrifice its legitimacy for any cause, let alone in an attack upon a foundational institution of public life. The rule of law is the first casualty in the judicial assault on marriage.