Second, Kennedy writes, marriage is a distinctive institution: “It supports a two-person union unlike any other in its importance to the committed individuals.” Here, he points to the Court’s opinion in Griswold v. Connecticut, which affirmed the right of married couples to use birth control. “Same-sex couples have the same right as opposite-sex couples to enjoy intimate association.”

But then, the decision takes an interesting turn: The Court seems to flip the oft-used reasoning of same-sex marriage opponents, who claim that gay marriage is harmful to children and families, and disruptive to the longstanding order of American society. In the oral arguments for Obergefell, several justices raised this very question—even Breyer, who joined in the decision, said that marriage between a man and a woman “has been the law everywhere for thousands of years. Suddenly you want nine people outside the ballot box to require states to change [this configuration].” But on Friday, Breyer joined four of his colleagues to do exactly that.

“Protecting the right to marry ... safeguards children and families and thus draws meaning from related rights of childrearing, procreation, and education,” Kennedy writes. Not all straight married couples have children, and they’re certainly not required to do so by law, he reasons; the same rule should apply to gay married couples. But more importantly, for those gay couples that do want to have kids—including the many couples who adopt or have children using the genetic material of one parent—that their unions are less than marriage under the law creates a “more difficult and uncertain family life. The marriage laws at issue thus harm and humiliate the children.”

Finally, Kennedy affirms that marriage is “a keystone of the Nation’s social order.” It is the institution at the center of the United States’ legal and educational structures, and because of this, “it is demeaning to lock same-sex couples out of a central institution of the Nation’s society, for they too may aspire to the transcendent purposes of marriage.”

“Rising from the most basic human needs, marriage is essential to our most profound hopes and aspirations,” Kennedy writes. This is, perhaps, the most striking argument of all, for it is an argument about the nature, significance, and dignity of marriage itself. “The ancient origins of marriage confirm its centrality, but it has not stood in isolation from developments in law and society,” Kennedy writes, but the “institution—even as confined to opposite-sex relations—has evolved over time.”

The dissents from Alito, Roberts, Thomas, and Scalia are scathing. The chief justice argues that the Court has stepped far beyond its bounds, stating simply, “this Court is not a legislature.” Like his colleagues in the majority, he delves into the history of marriage, even giving a nod to one of the favorite arguments of gay-marriage opponents: that legalizing gay marriage is essentially a slippery slope. In fact, he writes, the leap from heterosexual marriage to same-sex marriage is “much greater than one from a two-person union to plural unions, which have deep roots in some cultures around the world.” His conclusion: “The majority expressly disclaims judicial ‘caution’ and omits even a pretense of humility, openly relying on its desire to remake society according to its own ‘new insight’ into the ‘nature of injustice.’ … Just who do we think we are?”