It happened on campus.

Once upon a time, the foundation of an American college education was common sense. Common sense realism was the philosophy young Americans learned in U.S. colleges. In the words of the great American historian, Arthur Herman, “Common Sense Realism was virtually the official creed of the American Republic.” Another great American historian, Allen Guelzo, made that point in this way in his lecture series, “The American Mind”: “Before the Civil War, every major [American] collegiate intellectual was a disciple of . . . common sense realism.”

According to Guelzo, American professors continued to be common sense realists until a political revolution in academia around the beginning of the 20th century pushed them out, ending an academic tradition that, since the time of the American Founding meant mastering common sense and learning to think like an American.

That the pivotal role of common-sense realism in American thinking is today unknown to most Americans is testimony to the astonishing success and thoroughness of that campus revolution.

As you know, we have had another revolution on campus since the one that broke with the tradition of the Founders. I refer of course to the revolution of the 1960s. It populated American campuses with politically radicalized professors who quickly put an end to the tradition that had replaced common sense realism. As recently as the ’60s it was still possible to get an education on campus if you made the effort, though common sense realism was nowhere to be found in the curriculum. If you have been following what has been happening at your alma mater or elsewhere in academia, you will already know that the focus is no longer education. Education has been replaced by political indoctrination in an ever-changing array of multiculturalism and political correctness.

This then is in outline the story of how we have a political Left that rejects America. They learned to think that way on campus. This story also helps explain what ails so many in the Republican leadership. They went to the same universities. While there, they were exposed to the same bad influences. More important, they were not given rigorous instruction in how to think like an American. The new postmodern Left’s political ideas are a rejection of the Founders’ idea of America, and the often confused responses by those who run for office in opposition to the Left reveal their uncertain grasp of the American Founders’ ideas.

But what is this “common sense realism” that once marked the education of America’s elite? Herman defines it in this way:

The power of common judgment belongs to everyone, rich or poor, educated or uneducated; indeed, we exercise it every day in hundreds of ways. Of course, ordinary people make mistakes—but so do philosophers . . . On some things, however, like the existence of the real world and basic moral truths, they know they don’t have to prove it. These things are . . . self-evident, meaning they are ‘no sooner understood than they are believed’ because they “carry the light of truth itself.”

The core idea of common sense realism is that there are self-evident truths. Common sense realists would say it is only because we can know self-evident truths that we can know anything at all. Self-evident truths are the foundation of human understanding, and we know self-evident truths by means of our common sense. The philosophy of common sense realism is all about self-evident truths.

Does that phrase “self-evident truths” catch your attention? Yes, that is the familiar phrase from the Declaration of Independence, and yes, when Jefferson and the other Founders spoke of self-evident truths they were revealing their reliance on common sense realism—which by the way, was a way of thinking that was reinforced in college, not undermined by it.

Ordinary Americans are for the most part still common sense realists, even if they have never heard of the philosophy of common sense realism and especially if they have never been to college. We can turn to Abraham Lincoln for a good example of that. You have probably heard this one before: “If you call a tail a leg, how many legs would a dog have? Four, because, even if you call it a leg, it’s still a tail.” Of course, this is only ordinary, garden-variety common sense. But the philosophy of common sense realism taught in American colleges during Lincoln’s time was deeply rooted in the common-sense thinking of ordinary Americans.

The powerful affinity between the common sense thinking of ordinary Americans and the thinking of the people who once constituted America’s elite explains why in former times they understood each other in a way that now has been lost.

The Founders believed Americans could govern themselves because they had faith in the American people. Here is Thomas Jefferson sounding very different than politicians today who speak of Americans as “bitter clingers” or “deplorables”: “State a moral case to a ploughman and a professor. The former will decide it as well and often better than the latter, because he has not been led astray by artificial rules.” The enormous gulf that has opened up between the thinking of ordinary citizens and the thinking of our ruling elite once did not exist.

One final point: common sense realism disappeared because it lost a political battle, not because it lost an intellectual battle. It is still as powerful intellectually today as it was when it was politically powerful because it was the philosophy of the Founders and the philosophy of America for long after the Founding. Above all, it is still powerful because it is the truth. It is up to us to recover it.