Because a book of mine has that phrase in the title, people frequently offer me their thoughts about common sense. Over time, this has amounted to a kind of informal and unscientific poll. Here are the results so far: evidently, there is general agreement that common sense has fallen on hard times in America. From "common sense has become so uncommon" to "whatever happened to common sense anyway?," the responses agree that American life has been trending away from common sense.

And it is obvious to anyone that common sense is not just fading away for reasons unknown. Common sense has been reeling from an all-out frontal assault. We need only to consider political correctness. Political correctness is the rejection of common sense in our political discourse. The proponents of P.C. demand that schools let boys into girls' bathrooms and that universities protect college students from words and ideas that might upset them. The P.C. overlords simultaneously demand that America bring in large numbers of Muslims from the jihadi-infested Middle East and that American citizens be deprived of the means to defend themselves and their families from jihadists.

But the war on common sense goes far beyond the political assault on the 1st and 2nd Amendments. Since academia is ground zero for political correctness and the progressive left, there is also an assault on rational standards in higher education. Steve Hayward has been chronicling the ongoing absurdity for us. In a recent posting, we learn that three women videotaped themselves watching the 17th season of ABC"S The Bachelor, then talked about it afterward, and turned it into a Ph.D.! Even worse, the Ph.D. was awarded by the University of Utah. The rot in academia has spread from elite private universities in progressive regions all the way to public universities in conservative states.

It was not ever thus. When America knew itself, common sense was the coin of the realm in American thinking, both in academia and in ordinary life.

The philosophy of common sense – called "common sense realism" – once reigned supreme in American higher education. Allen Guelzo, the distinguished American historian, made that point in this way in his truly great lecture series, "The American Mind":

Before the Civil War, every major [American] collegiate intellectual was a disciple of ... common sense realism.

Please notice what an extraordinary statement this is. Professor Guelzo does not say "most" or "nearly all"; he says "every." This speaks to the extraordinary importance of this philosophy to the original American Republic. Identified with the Scottish philosopher Thomas Reid and his followers, it was, in the words of another great historian, Arthur Herman, "virtually the official creed of the American Republic." The Founders were masters of the thought of Reid and the tradition he belonged to.

For more than a century after the Founding, studying those thinkers was part of what it meant to be an educated American. Here is what the distinguished British historian Lord Acton found when he visited Harvard in 1853:

The first year they read a few books of extracts from classical authors, and a bit of Horace and Cicero[.] ... Next year: 2 books of Homer, 2 or 3 plays, some Horace, Cicero[.] ... In the third year Reid becomes a text-book.

Not extracts from Reid, but "a text-book" – testimony to Reid's importance.

To be clear, common sense realism exists in two varieties. There is the garden variety, which you and I rely on in our daily lives and which we usually just call common sense. If you believe that a boy in a tutu and a tiara who claims he identifies as a girl is a boy, then you are a common sense realist.

Lincoln spoke for all of us garden-variety common sense realists when he famously asked and answered this question: "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."

In contrast, Professor Guelzo is referring to common sense realism in its second variety. It is philosophy of great rigor and reach for philosophers who embrace common sense.

The fact that educated Americans and ordinary Americans alike were common sense realists goes a long way to explain what made America extraordinary. Alexander Hamilton and Abraham Lincoln were masters of common sense realism. That the Americans they addressed, educated or not, were also common sense realists did much to make it possible for Hamilton and Lincoln to reach voters on the extraordinarily high level of thinking we find in The Federalist Papers and in Lincoln's speeches.

So what, then, has happened to common sense? It has fallen victim to the progressive left's rejection of the Founders' vision. Of course, the progressives reject the Constitution, the Electoral College, and all of the creations of the Founders, but that is not sufficient for their purpose. They also must go on to reject the common sense realism of the Founders. Since that philosophy is rooted in ordinary common sense, ordinary common sense must go, too.

Donald Trump calls himself a common sense conservative. Does his election signal America's return to common sense? It is too soon to tell. Certainly, the enemies of common sense will fight – and they occupy fortified positions. Tenured professors in colleges and universities and government employees at every level cannot be fired, and they are more dedicated to fundamentally transforming America according to the progressive vision than they are to teaching or to serving the taxpayers who pay their salaries. We may not have yet seen the worst of what they will do to resist the threat of a return to common sense.

If the outcome of this fight matters to you, please consider trying to find a way to lend a hand.

Robert Curry is the author of Common Sense Nation: Unlocking the Forgotten Power of the American Idea from Encounter Books. You can preview the book here.