For conspiracy theorists, “Pizzagate” didn’t end when a man brought a gun to Comet Ping Pong, a Washington pizza restaurant, in a misguided attempt to rescue nonexistent child sex slaves. Some conspiracy theorists see Edgar Maddison Welch’s effort as the latest “false flag,” a coverup or distraction orchestrated by the government or other powerful figures. (Jose Luis Magana/AP)

Last week, a heavily armed man stormed a popular family pizzeria in Washington, on the theory that it harbored child sex slaves. He shot the lock off an interior door and pointed his assault rifle at one of the pizza chefs before surrendering to police — but not before searching for signs of an elaborate sex slave scheme at the restaurant.

Of course, there was no such insidious scheme. It was a fiction created through feverish chatter in social media, the latest in an alarming trend of fake news stories.

Much has been written about these proliferating “news” stories and their possible effects on the 2016 election. As many have noted, the increasing reliance on the Internet for news has made it harder to distinguish fact from fiction. And growing political polarization leads many to seek confirmation of their biases rather than facts.

But something deeper is involved, as Plato can help us understand.

In perhaps the best-known pages from his celebrated “Republic,” Plato’s character Socrates asks his interlocutors to imagine prisoners chained to a cave wall. They have lived there their entire lives, seeing nothing but the shadows on the wall. Naturally, he observes, “what the prisoners would take for true reality is nothing other than the shadows.”

After one prisoner is released to the outside world, he comes to realize the difference between the shadows and reality.

The Allegory of the Cave can be read in many ways, including politically. The cave prisoners are epistemologically impaired, unable to distinguish fact from fiction, in part because of external manipulations. Socrates’s account of the cave includes powerful and manipulative “puppeteers” who cast the shadows that the prisoners mistake for reality. In Plato’s day, those puppeteers were often “sophists” — skilled and well-compensated mercenary orators who, Plato alleges, constructed arguments for money without regard for their truth or falsehood.

Today’s puppeteers include the purveyors of fake news. Like the sophists, fake-news authors are typically more interested in profiteering than in informing citizens.

But manipulation for profit isn’t the only issue, according to Plato. He was a citizen of democratic Athens, the birthplace of Western democracy, and knew democracy intimately. Democracies, he wrote, celebrate two political values above all: liberty and equality. While democratic citizens instinctively rally around these ideas (and Plato is sensitive to their virtues), he also fears that they can give birth to serious social pathologies.

How so? Liberty includes “freedom of speech,” he notes, and therefore the “license in it to do whatever one wants.” Democratic citizens, in other words, are free to say both what is true and what is false.

Plato might not find this freedom of speech so problematic if it weren’t combined with a pervasive ethos of “equality [for] equals and unequals alike,” as he puts it, in which opinions “are all alike and must be honored on an equal basis.” The noble side of this equality is that no opinion should be dismissed just because of anyone’s class or origins. But there’s an ignoble side, he emphasizes, that puts truth and falsehood on equal footing. And when citizens have the liberty to insist on falsehoods, they’ll be competing, in the marketplace of ideas, with genuine, demonstrable truths.

And this democratic equality, Plato explains, tends to be especially dismissive of authority — the parents, teachers and philosophers he thought should govern in a just society.

We’ve all seen how lies can obscure the truth and how that combination of liberty and respect for equality has been complicating public policy. Consider the overwhelming evidence that fossil fuel use is changing the climate, or the expert research showing no connection between vaccinations and autism — and then the citizens who choose instead to believe corporate interests, celebrities or conspiracy theorists, as if their speculations were equal to scientific expertise.

Fake news is just the latest manifestation. In a culture where speech is free and all “opinions” are equal, it gets harder and harder for citizens to tell reputable from disreputable sources of news.

Distressingly, Plato tells us that this is a natural result of mature democracies.

Plato famously offers a solution in his “Republic”: Replace democracy with an aristocratic regime ruled by uniquely gifted and elaborately trained philosophers who are professionals at telling truth from falsehood.

Even if that were desirable, this solution is as unlikely to be realized today as it was in ancient Athens. Plato offers more appealing solutions in his later dialogue, “The Laws.” There he suggests a mixed constitution that borrows from many types of regimes, including democracy and expert rule, allowing some especially well-informed “opinions” to get special consideration in public deliberations. He also promotes an educational system that inculcates a love of the truth. “Truth is the leader of all good things,” he writes, “for gods and of all things for human beings.”

If citizens make it a priority to pursue truth, our democracy has some hope. But Plato’s “Republic” advises us that, without special interventions, the pathologies leading to fake news will be with us for a long time.

Note: The author dedicates this essay to Gregg Franzwa (1944-2016), who shared his love of Plato and philosophy with generations of grateful students at Texas Christian University.

David Lay Williams is a professor of political science at DePaul University and the author of “Rousseau’s Platonic Enlightenment” and essays on Plato’s political philosophy, and is currently writing a book on economic inequality in the history of political thought, under contract with Princeton University Press.