We’re slipping backwards. The steady progress which Western societies had been making toward empiricism, rationalism and tolerance is going into reverse.

We are becoming more tribal, more intuitive, more impervious to evidence. And oddly, it’s happening, not as a result of war or poverty, but during a sustained rise in living standards.

Consider, to pluck a recent example, the New Yorker’s decision to drop Steve Bannon from its “ideas festival.” Bannon isn’t my cup of tea ideologically — I’m a mainstream small-government conservative, whereas he pals about with Left-wing European populists who happen to be anti-immigrant (and are therefore inaccurately labeled “far-Right”). But, having invited him, it was extraordinary to disinvite him. Quite apart from the rudeness, the cowardice and the self-defeating publicity, it showed how far the New Yorker — and, indeed, the liberal media generally — have moved from genuine liberalism, in the sense of openness to at least hearing different ideas.

It is this aspect of the whole affair that is the most troubling and yet, sadly, the least remarkable. The New Yorker was effectively saying, “Your take on the world is so jarring that it may not be heard.” That attitude is the opposite of liberalism. Liberalism, at least the English-speaking strain which is its best and truest variant, traces its pedigree back via John Stuart Mill and John Locke to John Milton, the Puritan poet whose dislike of authority was so pronounced that, in Paradise Lost, he couldn’t help portraying God as lordly, arid and cruel. In 1644, at the height of England’s civil and religious conflicts, he published Areopagitica, the first modern defense of freedom and free expression.

Milton’s argument was, at the time, utterly revolutionary. Truth, he argued, was not something to take on authority from priests, prelates or princes. Rather, a process of debate would allow good ideas, over time, to drive out false ones. “Though all the winds of doctrine were let loose to play upon the earth, so Truth be in the field, we do injuriously, by licensing and prohibiting, to misdoubt her strength,” wrote the ornery Cromwellian civil servant. “Let her and Falsehood grapple; who ever knew Truth put to the worse, in a free and open encounter?”

Does anyone even read Milton any more? Or Locke? Or Mill? Because we seem to be turning our backs with astonishing rapidity on the central idea of the Enlightenment, namely that we don’t know everything there is to know, and that the best way to improve our understanding is to allow different ideas to be heard.

To be fair, that notion is a counter-intuitive one. The human brain is designed to make shortcuts and find patterns. The same mental wiring that makes us prone to conspiracy theories, and that makes us blame natural disasters on human wickedness, also makes us want to look for all truth in some special book. Not necessarily a sacred book — Marxists see themselves as the ultimate rationalists, yet they cling to the dogmas of their foundational texts as uncritically as any Wahhabi does the Koran.

Only in very recent times has Milton’s insight spread — and, even then, largely in the West. Most people cling to the rules-of-thumb, what psychologists call heuristics, that evolved in our hunter-gatherer brains. For example, our natural inclination is to judge an idea on the basis of the person proposing it rather than on its merits. Having taught ourselves not to do that — to think about the idea itself — we now seem to be reverting to the even older heuristic, by which we judge ideas based on the tribe they come from. My tribe good, your tribe bad.

Tribalism is now the basis of American politics. Partisanship is old, but the determination to believe different facts on the basis of who cites them is new. Yet we shouldn’t be surprised, for the notion of relative truth, truth defined by the status of the person speaking it, is now mainstream in universities — which ought to be the strongest redoubts of Enlightenment values.

Take a statement like “Islam has a problem with homosexuality.” How that statement is received will be almost wholly determined by whether the speaker is Muslim or non-Muslim, gay or straight, rather than by the intrinsic truth of the assertion.

Identity politics is really a revival of the pre-modern notion of caste — that is, of a person's status fixed at birth. The sheer persistence of that idea across continents and centuries suggests that our notion of personal autonomy is the more difficult one to sustain.

The values that make an open society possible are not innate. We have to be taught that things we don’t know might have value, that people we dislike might have wisdom, that disagreement does not imply immorality. Are we still teaching our young people these lessons? To ask the question is to answer it.