They are questions that have evaded simple answers for over 200 years: Which religious institutions can get tax funding? Is it “bigotry” to exclude religious schools? Or are the bigots the ones hoping to cram their religion down the throats of taxpayers? In the latest round of this debate, the U.S. Supreme Court on Tuesday ruled 5 to 4 states with voucher programs must allow private religious schools to participate. Both sides made historically based arguments, but because they focused on the wrong period, they ignored the most important lesson from America’s past. Although ideas about religion and bigotry have changed dramatically over the centuries, the guiding principle for using tax money properly in public schools has not.

At issue in this case was a school voucher policy in Montana. Like 37 other states, Montana’s constitution banned the use of tax money to pay for religious schools, seeing it as a clear violation of the separation of church and state.

Parent Kendra Espinoza objected. Building on momentum from recent school-religion cases, conservatives hoped her case would introduce a new normal. Now if Montana wants to maintain its voucher program, it can no longer exclude religious schools solely on the basis of their religious nature.

The case revolved around historical arguments. Conservative activists insisted Montana’s school-funding rule was the legacy of anti-Catholic “bigotry.” Montana’s constitution included language similar to a failed 1876 U.S. constitutional amendment, named for its famous sponsor, former senator and speaker of the House James G. Blaine (R-Maine). The Blaine Amendment tried to restrict funding for religious institutions. As it specified, “no money raised by taxation … shall ever be under the control of any religious sect.” The federal amendment failed, but like 20 other states in that period, Montana inserted a similar clause in its 1889 constitution. Those states joined 17 states that already had such provisions before the proposed Blaine amendment.

Religious conservatives argue this was simply a thinly veiled way to discriminate against Catholics. As Justice Clarence Thomas pronounced in an opinion 20 years ago, state Blaine amendments came about “at a time of pervasive hostility to the Catholic Church.” In the 1870s and 1880s, Thomas wrote, “it was an open secret that ‘sectarian’ was code for ‘Catholic.’”

Montana, however, insisted the relevant history in Espinoza v. Montana Department of Revenue was not from the 1870s, but from the 1970s. In that decade, the state revised its constitution and Montanans decided overwhelmingly to keep its Blaine provision. This choice was not about anti-Catholicism, which had faded by the 1970s, but about protecting against government entanglement with religion.

But both sides ignored the fact that a key word — sectarian — had a significant meaning in American history well before the debates over the Blaine Amendment. That history, from the 1810s and 1820s, changes how one understands these provisions.

In that era, cities such as New York were trying to figure out what public education should look like. At the time, the lines between public and private schools were not so clear. Tax-funded common schools often charged tuition and privately run schools often received funding from governments.

These debates produced a messy history, but Americans tended to agree on one thing: They never liked using tax money to pay for schools that taught controversial religious doctrines.

To them, therefore, the word “sectarian” was not simply “code” for anti-Catholicism. Instead “sectarian” referred to a school that taught any religious idea that was not generally agreed upon by all Christian denominations.

This history has been obscured because early public schools were chock-full of religion. For the most part, school leaders thought differently than we do about the proper role of religion in public institutions. They saw no problem with using tax money to teach a generic kind of Christianity.

For instance, in 1814, the leaders of New York’s Free School Society simply assumed their tax-funded schools for the public would actively promote Christian religion. Every student read from the Bible every day in school, and on Tuesday mornings, all students were pulled out of school to attend catechism classes at their church of choice, including both Catholic and Protestant denominations. Students were exhorted to go to their family’s church on Sunday and their attendance at those services and events was tracked by the society as a sign of success. Moreover, in 1819, the Free School Society proudly proclaimed its goal to use their tax-funded schools “to inculcate the general principles of Christianity.”

But, crucially, the public had little appetite for supporting schools that did more than convey the “general principles of Christianity”; they did not want to use taxes to pay for schools that actively taught religious ideas in dispute. For example, taxes could fund schools where children read biblical passages about baptism, but not where children learned that people should only be baptized as adults — a controversial idea at the time.

This also meant taxpayers refused to pay for ideas that were held only by one sect or denomination. That applied to Catholicism, but also to many other religious beliefs and ideas. One 1822 case from New York illuminated this distinction. In that year, Bethel Baptist, a school that taught Baptist doctrine, applied for state funding. The city’s Common Council eventually turned down the request. In the language of 1822, they refused to mingle public school funding with “the promotion of private and sectarian interests.”

This history reveals that Blaine’s anti-Catholic supporters in the 1870s manipulated long-standing American loathing for “sectarian” schools, but they did not invent it. Long before Blaine proposed his amendment, the American public recoiled from sending tax money to schools that taught controversial religious doctrines.

During the 20th century, America evolved away from the old shared assumption that public schools should teach “general principles of Christianity.” In the 1960s, for example, the Supreme Court recognized even bland prayer was controversial. The court acknowledged traditional public school Christian devotions unfairly excluded far too many people, including non-Christians and nonbelievers. A new principle developed that any teacher-led religion represented “excessive entanglement” between church and state.

Today, therefore, instead of worrying about taxes funding controversial religious ideas held only by one denomination, we acknowledge the fact that funding any religious idea is inherently controversial, given the diversity of American religion and nonreligion. We also no longer talk about “sectarian” ideas. But all that has done is broaden the basic provision enshrined long before the 1870s: American public education should use tax dollars to teach children how to read, write and become better citizens, not to teach them any religious ideas.

In his majority opinion, Chief Justice John G. Roberts Jr. wrote that no “‘historic and substantial’ tradition supports Montana’s decision to disqualify religious schools from government aid.” But in reality, to the contrary, the longest tradition in American public education has been precisely this: a stern unwillingness to spend taxpayer money to teach any religious idea not considered to be nearly universally held.