I gather that some readers were puzzled by my use of the term “derp” with regard to peddlers of inflation paranoia, even though I’ve used it quite a lot. So maybe it’s time to revisit the concept; among other things, once you understand the problem of derpitude, you understand why I write the way I do (and why the Asnesses of this world whine so much.)

Josh Barro brought derp into economic discussion, and many of us immediately realized that this was a term we’d been needing all along. As Noah Smith explained, what it means — at least in this context — is a determined belief in some economic doctrine that is completely unmovable by evidence. And there’s a lot of that going around.

The inflation controversy is a prime example. If you came into the global financial crisis believing that a large expansion of the Federal Reserve’s balance sheet must lead to terrible inflation, what you have in fact encountered is this:

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I’ve indicated the date of the debasement letter for reference.

So how do you respond? We all get things wrong, and if we’re not engaged in derp, we learn from the experience. But if you’re doing derp, you insist that you were right, and continue to fulminate against money-printing exactly as you did before.

The same thing happens when we try to discuss the effects of tax cuts — belief in their magical efficacy is utterly insensitive to evidence and experience.

Now, not every wrong idea — or claim that I disagree with — is derp. I was pretty unhappy with the claim that doom looms whenever debt crosses 90 percent of GDP, and not too happy with the later claims that the relevant economists never said such a thing; that’s what everyone from Paul Ryan to Olli Rehn heard, and they were not warned off. But there has not, thankfully, been a movement insisting that growth does too fall off a cliff at 90 percent, so this is not a derp thing.

But there is, as I said, a lot of derp out there. And what that means, in turn, is that you shouldn’t pretend that we’re having a real discussion when we aren’t. In fact, it’s intellectually dishonest and a public disservice to pretend that such a discussion is taking place. We can and indeed are having a serious discussion about the effects of quantitative easing, but people like Paul Ryan and Cliff Asness are not part of that discussion, because no evidence could ever change their view. It’s not economics, it’s just derp.

Now, saying this brings howls of rage, accusations of rudeness and being nasty. But what else can one do?