Mark Thoma sends us to John Cassidy on the absence of really new ideas in this crisis — largely because we didn’t need new ideas, all we needed for the most part was to remember things that we somehow forgot.

This is a theme dear to my heart. The crisis we’re in is not something unprecedented. It’s a close cousin to the Great Depression — milder, but recognizably the same sort of thing. And we understand — or used to understand — how the Depression happened, and what to do in such a situation. Most of what’s required are fairly straightforward translations of existing concepts. For example, we have a pretty good understanding of bank runs; extending that framework to shadow banking requires little more than the understanding that repo and other kinds of short-maturity obligations are, from an economic point of view, more or less equivalent to deposits.

So how is it that policy is so confused and lost?

I’ve been arguing for a while that much of the economics profession has lost its way, recapitulating old errors because it made a point of unlearning what Keynes taught. But it’s not just economists who willfully threw away hard-won insights.

On Monday night we had a panel discussion of the euro crisis at Princeton — me, Chris Sims, Hyun Shin, Markus Brunnermeier. I was struck by some of what Sims had to say. He pointed out that central banks have always had a wider mandate than simply guaranteeing price stability; they’ve always served as lenders of last resort, including having a standby capacity to finance the government in times of need. And there are good, well-understood reasons for this wider mandate. Yet the creators of the euro essentially threw away hard-won wisdom — stuff that Bagehot knew in the 19th century! — to create a stripped-down central bank without the powers or flexibility that history has shown are necessary. What were they thinking?

The result of all this is that the supposedly sober, serious people are actually radicals insisting that we can make the economy work in ways that it has never worked in the past — hence the embrace of magical thinking on expansionary austerity and the power of structural reform. Meanwhile, the irresponsible bearded professors are actually the custodians of traditional wisdom.

And those who are determined to forget the past run a high risk of reliving it — which is why we’re in the state we’re in.