In a plain-spoken essay in New York magazine last month, well-known (and self-described) liberal commentator Jonathan Chait explored a deep philosophical divide on the progressive side of American politics. Much discussed already, at least in liberal circles (it was recommended to me by a liberal friend), it shouldn't be missed.

The progressive schism Chait describes is both a little frightening and in another way encouraging. It surely plays its part in the bitter unpleasantness of political debate in America today.

Chait's concern is "political correctness" — a "movement," he says, that has "returned" after "a long remission."

Not all Americans were aware that there had been much of a hiatus for the spirit of intolerance among some on the left — the hypersensitivity to any hint of racism, sexism, classism, or any other lapse into an ever-multiplying and -diversifying assortment of forbidden attitudes.

But the explosive growth of social media in recent years, Chait says, has given the "p.c. movement" new power to mount punitive campaigns and inquisitions far beyond its native land on college campuses — realms that remain oppressed by its speech codes, drives to disinvite disfavored speakers and its newer demands for "trigger warnings" alerting students to the imminent approach of troubling ideas.

But beyond all that, Chait writes, "political correctness is a style of politics in which the more radical members of the left attempt to regulate political discourse by defining opposing views as bigoted and illegitimate."

He calls this "a system of left-wing ideological repression" that is "antithetical to liberalism."

Candidly, this last claim comes as something of a surprise to a person of a more conservative habit of mind. The notion has long seemed tolerably widespread among liberals that only some kind of moral corruption or, at least, moral confusion can explain someone's disagreeing with progressive conclusions. This often seems to explain an eagerness on the left to declare factual debates "over" (at least sometimes meaning that their opponents should no longer be heard) whether the topic is the effect of some economic policy or climate change.

But Chait insists that liberals, on the one hand, and "leftists" (the p.c. enforcers), on the other, simply don't want the same things, beyond both seeking more equality in society. Liberals, he says, "hold to the classic Enlightenment political tradition that cherishes individual rights, freedom of expression and the … free political marketplace. …" He even allows that "most conservatives" cherish these principles, too.

In fact, without quite saying that liberals ultimately have more in common with conservatives than with the p.c. extremists, Chait does say that "the p.c. left is actually more philosophically threatening. It is an undemocratic creed."

At a time when fanaticism and factional infighting on the right have generally gotten more attention, Chait's declaration of a kind of civil war on the left is certainly striking. It's also part of something like a trend.

Last year, a group of prominent supporters of same-sex marriage issued a well-circulated statement titled "Freedom to Marry, Freedom to Dissent: Why We Must Have Both" ("Persuade, don't punish gay rights opponents" in the Star Tribune, May 1). It decried the punitive and censorious turn the marriage equality crusade had too often taken.

And last fall many liberal pundits (Chait among them) joined conservatives in pushing back against the advent of "affirmative consent" rules on some college campuses as an illiberal overreaction to reports of a "rape epidemic" there. (The debacle surrounding Rolling Stone's faulty gang rape report at the University of Virginia soon followed.)

Conservatives may be tempted to be amused that thoughtful liberals are only now coming to grips with the danger of Orwellian tendencies within their ranks. But they would do better to sober up, welcome a bit of soul-searching on the left — and try something similar themselves.

The right's most extreme wing may be less authoritarian than anarchistic (and that more in theory and rhetoric than in practice). But its disdainful rejection of democratic compromise, its tolerance of bigotry and its fantasies of dismantling more or less the whole of modern government leads to recklessness.

It may be that if we are ever to enjoy a more constructive and less toxic political debate, both of our chief political creeds will need to purge, or anyway tame, extreme elements that in recent years have become distorting and destructive — at least, if they still can.

Chait's "classic Enlightenment political tradition" may be the place to start (some conservatives may prefer to emphasize its roots in the Judeo-Christian tradition, but whatever).

Does a critical mass of Americans truly still cherish individual rights, freedom of expression and a free political marketplace above all — still caring more about these things than about whether one's own political ideology prevails?

Chait's manifesto is a good sign. But one sometimes wishes the answer were more obvious than it is.

D.J. Tice is at Doug.Tice@startribune.com.