In a wave of recent decisions, one court after another across the nation has held that laws denying same-sex couples the freedom to marry violate the Constitution. Indeed, we now have reached the point where courts routinely find the arguments in defense of such laws simply implausible.

The constitutional provision at issue in these cases is the Equal Protection Clause of the Fourteenth Amendment. The Equal Protection Clause provides that “No state shall ... deny to any person the equal protection of the laws.” Although the text seems straightforward on its face, the meaning of the Clause cannot be found in its words.

Every law treats people differently. People under a certain age cannot drive. People who haven’t graduated from law school cannot practice law. Murderers are punished differently than shoplifters. Rich people pay higher taxes than poor people. It goes without saying that such laws, and thousands more like them, do not violate the Equal Protection Clause, even though they treat people differently.

In giving meaning to the Equal Protection Clause, the Supreme Court has focused on several types of situations. As a general matter, the Court has held that a law that treats some people differently from others does not “deny ... the equal protection of the laws” if the difference in treatment is rationally related to a legitimate government interest.

Under that standard, all of the hypotheticals I posited above are constitutional. Indeed, in the history of American constitutional law, few laws have ever flunked that standard. An example of a law that would flunk the rational basis test is one that prohibits people born on Tuesdays from driving. There is no conceivable justification for treating people born on Tuesday differently than other people in terms of driving.

In other situations, though, the Supreme Court has held that, in order to pass constitutional muster, a challenged law must meet the demands of something called “heightened scrutiny.” When heightened scrutiny applies, the government must demonstrate not only that the distinction drawn by the challenged law is rational, but that it is necessary to further an important government interest. This is a much higher standard of justification.

There are two situations in which heightened scrutiny applies. First, heightened scrutiny applies when a law discriminates against a group of people who have historically been discriminated against and who cannot reasonably be expected to change the characteristic that is the target of the discrimination. A law prohibiting African-Americans to serve as jurors or prohibiting women to be lawyers falls into this category. Such laws are deemed presumptively unconstitutional under the Equal Protection Clause, because discrimination against such groups is thought to be especially unfair and especially likely to be the product of prejudice.

Second, heightened scrutiny applies when a law treats people differently with respect to a fundamental interest. Laws prohibiting unemployed people from moving into a state or prohibiting people who haven’t graduated from high school from voting are tested by heightened scrutiny, rather than rational basis review, because discrimination with respect to such fundamental interests as the right to move from one state to another and the right to vote are thought to be especially problematic under the Equal Protection because they implicate core constitutional values.

That brings us back to laws denying same-sex couples the freedom to marry. When such laws were first challenged only a few years ago, gay rights advocates generally assumed that these laws were rational, but maintained that they should be tested by heightened scrutiny either because they discriminated against a group (homosexuals) who share the essential characteristics of African-Americans and women (that is, they have suffered a history of oppression and are unable to change their sexual orientation), or because they discriminated between people in terms of a fundamental interest: marriage.

What is fascinating about the recent spate of decisions invalidating laws that deny same-sex couples the freedom to marry is that the judges have found it unnecessary to consider whether heightened scrutiny applies, holding instead that these law flunk even the rational basis standard.

A great example of this trend is the decision last week in DeBoer v. Snyder, in which federal district court judge Bernard A. Friedman, who was appointed to the bench by President Ronald Reagan, held that a Michigan law prohibiting same-sex couples to marry violates the Equal Protection Clause because it does not rationally further a constitutionally legitimate government interest.

In defense of the law, Michigan Governor Rick Snyder made two central arguments. First, he insisted that the state could rationally forbid same-sex couples to marry because children raised by such couples are less likely to succeed in life than children raised by opposite-sex couples.

Judge Friedman demolished this contention. To support his position, Governor Snyder presented a study purporting to prove the contention. Noting that this study was cooked-up by fervent opponents of gay marriage, Judge Friedman, after evaluating all the evidence, found the study “entirely unbelievable and not worthy of serious consideration.”

Judge Friedman concluded further that Governor Snyder’s claim that a concern for children was in fact the reason for the law was preposterous on its face. After all, Michigan law allows murderers, rapists, and convicted child-abusers to marry—as long as they marry a person of the opposite sex. That being so, the notion that the law prohibiting same-sex couples to marry was based on a concern for the well-being of their children was, in Judge Friedman’s words, nothing short of an “absurdity.”

Second, Governor Snyder argued that the law prohibiting same-sex couples to marry is rationally related to a legitimate government interest because it enforces the religious and moral beliefs of the state’s citizens. Judge Friedman emphatically rejected this explanation: “Many Michigan residents have religious convictions whose principles govern the conduct of their daily lives,” but “these views cannot strip other citizens of the guarantees of equal protection of the law. The same Constitution that protects the free exercise of one’s faith [also] prevents the state from ... enforcing private moral or religious beliefs without an accompanying secular purpose.”

Judge Friedman therefore concluded that the Michigan law denying same-sex couples the freedom to marry “does not advance any conceivable legitimate state interests,” and therefore violates the Equal Protection Clause of the Fourteenth Amendment.

The truly remarkable thing about this decision, and about the many similar decisions now emanating from courts throughout the nation, is that judges are now finding, one after another, whether appointed by Ronald Reagan or Bill Clinton, that laws forbidding same-sex couples to marry are simply irrational as a matter of law. We have come a long way.

I should note, by the way, that four Justices on the Supreme Court today—John Roberts, Antonin Scalia, Clarence Thomas, and Samuel Alito—continue to reject this conclusion and insist that states can constitutionally deny same-sex couples the right to marry. Happily, they are only four. The sad thing, though, is that they are no closer to sound constitutional judgment on this issue today than were those who defended the constitutionality of “separate but equal” were 60 years ago.