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.

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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.