“When men have realized that time has upset many fighting faiths,” U.S. Supreme Court Justice Oliver Wendell Holmes wrote in a famous dissenting opinion in 1919, “they may come to believe … the ultimate good desired is better reached by free trade in ideas — that the best test of truth is the power of the thought to get itself accepted in the competition of the market, and that truth is the only ground upon which their wishes safely can be carried out.”

Like any market, however, the marketplace of ideas needs regulation: In particular, its participants should be bound by norms of honesty, humility and civility. Moreover, every idea-trader should adhere to these principles.

Of course, politicians through the ages have polluted the marketplace of ideas with invective. But in American politics, surprisingly, there has been progress.

According to a study by the Annenberg Public Policy Center, there has been less incivility in Congress in recent years than in the 1990s or the 1940s. Republican Sen. Ted Cruz was widely condemned for his aggressive questioning of incoming Defense Secretary Chuck Hagel back in January. But casting aspersions on a nominee’s patriotism was the norm in the McCarthy era; it is less common today.

Academia, by contrast, appears to be moving in the opposite direction. A “social science” like economics is supposed to be free of partisan vitriol. Yet economists now routinely stoop to ad hominem attacks and inflammatory polemics.

As economists go, they do not come much mightier or more influential than Paul Krugman. A Nobel laureate who teaches at Princeton University, Krugman is also a columnist for the New York Times, whose commentaries and blog, “The Conscience of a Liberal,” are read with an almost religious fervor by liberal (in the American sense) economists and journalists around the world.

He is a Twitter superstar, with more than a million followers. A dozen ardent epigones blog in sync with him, re-posting the wisdom of the master.

Many people today naively believe that the Internet is an unmitigated boon for free speech. They underestimate the extent to which such a concentration of online power corrupts, as surely as all forms of power do.

Since Krugman and I began debating fiscal and monetary policy back in 2009, I have become increasingly alarmed by the way he abuses his power. Last week, I resolved to speak out in a three-article series, published squarely in the heart of the liberal blogosphere, the Huffington Post.

As historians are trained to do, I based my argument on the archives. By quoting his past writings, I showed, first, that Krugman’s repeated claims to have been “right about everything” in his economic commentary are false.

Although (like many others) he identified a housing bubble in 2006, he did not foresee the financial chain reaction that would fuel a global crisis. Having failed to predict the U.S. crisis, he then incorrectly predicted the imminent disintegration of Europe’s monetary union, publishing more than 20 statements on that subject in 2011 and 2012. He has never admitted these errors; on the contrary, he has retrospectively exaggerated his own prescience.

Second, Krugman’s claim that a vastly larger fiscal stimulus would have generated a more rapid economic recovery in the U.S. depends entirely on conjecture.

But the macroeconomic model on which he bases his claim can hardly be called reliable, given its manifest failures to predict either the crisis or the euro’s survival.

Moreover, at least one of his pre-crisis columns flatly contradicts his view today that current — or even higher — levels of federal debt carry no risk whatsoever. So he has no right to claim, as he has, “a stunning victory” in “an epic intellectual debate.”

Finally — and most important — even if Krugman had been “right about everything,” there would still be no justification for the numerous crude and often personal attacks he has made on those who disagree with him. Words like “cockroach,” “delusional,” “derp,” “dope,” “fool,” “knave,” “mendacious idiot,” and “zombie” have no place in civilized debate. I consider myself lucky that he has called me only a “poseur,” a “whiner,” “inane” — and, last week, a “troll.”

Far from engaging in Holmes’ free trade in ideas, Krugman has been the intellectual equivalent of a robber baron, exploiting his power to the point of driving decent people away from the public sphere — particularly younger scholars, who understandably dread a “takedown” by the “Invincible Krugtron.”

My preferred solution would be accountability. But I have given up hope that the New York Times will perform its proper editorial function.

So, instead, I would suggest the intellectual equivalent of an antitrust law. For every word that Krugman publishes, he must henceforth commit to having first read at least a hundred words by other writers.

I cannot guarantee that reading more widely will teach him honesty, humility, and civility. But it will at least reduce his unjustifiably large share of the marketplace of economic ideas.

As a Supreme Court justice, of course, Holmes opposed antitrust regulations. But his arguments in this area failed his own “test of truth,” for they lacked “the power … to get … accepted in the competition of the market.” Holmes accepted defeat with his customary grace. It is high time that Krugman — right or wrong — learned to behave that way, too.

Niall Ferguson is the Laurence A. Tisch Professor of History at Harvard University and a senior fellow of the Hoover Institution, Stanford University. His latest book is “The Great Degeneration: How Institutions Decay and Economies Die.” © 2013 Project Syndicate/Institute for Human Sciences (www.project-syndicate.org)

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