Recently there’s been a debate in the political blogosphere about “epistemic closure.” As far as I can tell, Julian Sanchez introduced the term here, in the following passage:
One of the more striking features of the contemporary conservative movement is the extent to which it has been moving toward epistemic closure. Reality is defined by a multimedia array of interconnected and cross promoting conservative blogs, radio programs, magazines, and of course, Fox News. Whatever conflicts with that reality can be dismissed out of hand because it comes from the liberal media…
And somehow this idea of epistemic closure among conservatives turned out to be really attention-grabbing. Lefty bloggers like it, naturally. Read Yglesias or Sullivan. But there’s also right-leaning NYT columnist Ross Douthat lamenting his fellow conservatives’ epistemic closure; there’s conservative-ish Jim Manzi criticizing right-wing talk radio host Mark Levin’s epistemic closure; there’s arch-conservative Jonah Goldberg (of “Liberal Fascism” fame) grumpily announcing that “epistemic closure” has already jumped the shark; and — well, I haven’t even scratched the surface. If you read mainstream political blogs, you’ve probably heard talk of epistemic closure.
The funny thing, though, is that the much older philosophical idea of epistemic closure has pretty much nothing to do with the sort of epistemic closure that all these bloggers are talking about.
Here’s my guess about what happened. Julian Sanchez studied philosophy as an undergrad (so says Wikipedia). He heard the term “epistemic closure” while he was in school. It got buried in his mind only to re-emerge later, by which time he’d forgotten its original meaning. (This diagnosis seems supported by this comment.) So he gave it a new meaning. And thus, by joining a fancy-sounding phrase to a politically incendiary idea, he created something new: a potent meme.
So Marc Ambinder needn’t worry that he “didn’t study philosophy much in college.” He’s still fully qualified to talk about epistemic closure in this new, non-philosophical sense that Sanchez has invented.
I’ve got nothing against the appropriation of old words for new purposes, but it’s also good to remember that you don’t learn new facts just by slapping a different name onto an old idea. And the Sanchezian notion of epistemic closure is a very old idea. It’s just closed-mindedness (or, perhaps better, insularity) with a fresh coat of paint. Conservatives have been accused of being closed-minded and insular since the first conservative was born — sometime during the Pleistocene epoch, I believe. If you want to show that conservatives are closed-minded, you don’t improve your case by calling closed-mindedness “epistemic closure.” (By contrast, if you want to make certain philosophers cringe a little, you may succeed by calling closed-mindedness “epistemic closure.”)
SEP’s detailed explanation of the philosophical kind of epistemic closure is here. Or check out Jonathan Kvanvig’s Phil Compass article, which I suspect many people will find slightly more accessible: Closure Principles By Jonathan L. Kvanvig, University of Missouri (May 2006) Philosophy Compass
The Philosopher's Eye 
As I note in passing in a more recent post, I didn’t go with “closed-mindedness” because I wanted to distinguish the collective/media phenomenon from any kind of individual disposition. The problem (as I see it) is not that conservatives happen to be individually closed-minded people; the lockdown is at the group level.
Oh, that’s embarrassing (to me). It looks like pretty much everything I say here is already said in your “Coda” post and/or in that Corner post you link. Oh well. Anyway, looking at your Coda post, I’m now thinking that the basic problem you’re describing is that conservatives deliberately surround themselves with misleading second-order evidence. I wonder if there’s a good old-fashioned plain-English word or phrase for that behavior.