History really matters in Obergefell v. Hodges, the Supreme Court case that has brought equal marriage rights to same-sex couples. Justice Anthony Kennedy, writing for the majority, relies on the history of marriage to lay the groundwork for his reasoning.

“Before addressing the principles and precedents that govern these cases,” the opinion begins, “it is appropriate to note the history of the subject now before the Court.” The opinion proceeds to make the crucial claim that marriage “has not stood in isolation from developments in law and society”; it has “evolved over time.” Why should this be necessary? Because the dissent, written by Chief Justice John Roberts and signed by the other three dissenters, embraces a very different view. Chief Justice Roberts calls marriage an “unvarying social institution enduring over all of recorded history.” It is, in his view, “a social institution that has formed the basis of human society for millennia, for the Kalahari Bushmen and the Han Chinese, the Carthaginians and the Aztecs.” In other words, more than one version of the history of marriage is in play.

The majority focuses squarely on the history of marriage as a civil institution within the U.S. constitutional order, after a brief bow to the institution’s “centrality” in “the human condition . . . for millennia and across civilizations.” The opinion sees that “the history of marriage is one of both continuity and change” in the United States. In this approach, the opinion follows—and explicitly cites—the amicus brief submitted by the American Historical Association. The court also cites a brief submitted by the Organization of American Historians, which describes the history of condemnation and criminalization of same-sex intimacy until recent decades. These citations are especially notable because the justices are not bound to read amicus briefs. (More likely their clerks do the reading initially, if at all.) In this case there were more than a hundred amici to choose among, and the court’s opinion cites only three besides the two historians’ briefs.

In drawing attention to ways that marriage in the United States has changed over time to admit new understandings of liberty and equality, the Court takes note of previous changes in marriage, long before the question of same-sex marriage came up. These “were not mere superficial changes,” the opinion says. “Rather, they worked deep transformations . . . affecting aspects of marriage long viewed by many as essential.” For instance, the opinion mentions the shift from arranged marriages to volitional contracts and the gradual demise of coverture once “society began to understand that women have their own equal dignity.” The understanding that marriage in the United States has had a long history of prior changes underpins the majority’s approach to the legitimacy of marriage between couples of the same sex and buttresses its assertion that “changed understandings of marriage are characteristic of a Nation where new dimensions of freedom become apparent to new generations.”

The Court’s constitutional reasoning interprets the due process and equal protection clauses of the Fourteenth Amendment together, concluding that the right to marry is so fundamental that it cannot be denied to couples of the same sex. The Court concedes that all of its supporting precedents concern “a relationship involving opposite-sex partners.” But, again sounding the theme of change over time, in constitutional interpretation as well as in marriage itself, the Court points out, “If rights were defined by who exercised them in the past, then received practices could serve as their own continued justification and new groups could not invoke rights once denied.”

By finding couples’ right to marry within the personal liberty protected by the due process clause, Justice Kennedy is engaging in so-called substantive due process. This means he is identifying rights not previously thought to be included in the “life, liberty or property” that the clause literally names. To do so, he relies on precedents beginning with birth control cases of the 1960s that extended personal liberty to include “certain personal choices central to individual dignity and autonomy, including intimate choices that define personal identity and beliefs.” For a practice to be included in the liberty interest, it should be, by constitutional precedent, “deeply rooted in this Nation’s history and tradition.” To the dissenters, the claim that same-sex marriage passes this test appears absurd: in their view, the issue at hand “is not the protection of a deeply rooted right but the recognition of a very new right,” Chief Justice Roberts writes, quoting Justice Samuel Alito’s objection in an earlier case.

Justice Kennedy and the majority reject the idea that a new right is being sought. Rather, leaning on a line of precedents that emphasizes personal choice, individual autonomy, and sexual equality, as well as numerous cases that say marriage is fundamental to individuals and a building block of society, the majority sees a new class of persons being admitted to a long-established right, as has happened before. “In defining the right to marry,” the majority says, previous cases “have identified essential attributes of that right based in history, tradition, and other constitutional liberties inherent in this intimate bond.” The majority sees those attributes applying equally to couples of the same sex. The majority opinion understands “the right to marry” to mean “the right to marry the person of one’s own choice,” the principle that brought down racial barriers of three centuries’ standing in Loving v. Virginia (1967).

Justice Kennedy ties this reasoning about liberty to additional reasoning about equality, based in another Fourteenth Amendment clause that has been crucial for rights expansion—the guarantee that citizens enjoy equal protection of the laws. He does this by invoking 1970s and ’80s precedents resulting from feminist successes in striking down “invidious sex-based classifications” in marriage law. (These efforts were often led by lawyer Ruth Bader Ginsburg, before she was on the bench.) Such precedents show that “the Equal Protection Clause can help to identify and correct inequalities in the institution of marriage.”

The majority thus advances both liberty (due process) and equality (equal protection) claims for same-sex couples’ marriage rights, on the assumption that successive constitutional interpretations can change the reach of both liberty and equality.  The dissenters do not accept this reasoning at all.

All of the dissenters formally object that the majority view is peremptory and unwarranted by the Fourteenth Amendment; they would have let the Sixth Circuit Court decision, which allowed four states to prevent same-sex couples from marrying, stand.  Accusing the majority of “stealing this issue from the people” by abusing substantive due process with over-interpretation based on nothing but the justices’ personal views, Justice Roberts’s dissent uses guilt by association in likening the opinion to the infamous Lochner decision of 1905 and even to the reprobated Dred Scott decision of 1857. Justice Antonin Scalia sees a “threat to American democracy” and accuses the majority of a “judicial Putsch.”

“To blind yourself to history is both prideful and unwise,” the chief justice writes. But which history does he have in mind? History, like the Constitution, can be read in more than one way. In the dissenters’ reading of history, marriage is an “unvarying social institution.” Changes in U.S. marriage law, including those brought about by judicial review, do not count. The majority has a different reading of history as well as of the Constitution. The majority sees marriage as a civil institution that has contained constitutionally impermissible inequities in the past, inequities that were addressed by judicial review. Taking a cue from the historians’ briefs, the majority understands previous changes to “have strengthened, not weakened the institution of marriage” and intends to continue on that path, removing another inequity with its current ruling.

A version of this article was first published by the American Historical Association magazine Perspectives on History.