By Paul Krugman.

Ah — so we learn that Ezra Klein’s Vox is under attack — as is the current Democratic agenda — because it’s “tired”, recycling ideas from the 60s and even earlier.

Indeed. You know what else is tired? The whole engineering agenda, which keeps recycling old ideas like conservation of energy and mass.

The point, of course, is that attacking ideas simply because they’ve been around for a long time is an act of deep intellectual laziness. What matters is whether the ideas work; clinging to old ideas only becomes a problem if you refuse to change in the face of contrary evidence. Yes, liberals call for progressive taxation and redistribution to limit inequality and reduce poverty; these aren’t new ideas, but they are ideas that work. Conservatives cling to supply-side economics, which is also an old idea — but the problem is that it’s an idea that keeps failing, but they refuse to accept that reality.

A case in point: remember the attempt to privatize Social Security in 2005? A fair number of allegedly liberal commentators supported that effort, on the grounds that we needed new structures for the information age, or something. In fact, a simple defined-benefit program makes even more sense in an unstable economic landscape. The age of the idea is neither here nor there.

And sometimes old ideas that have for whatever reason fallen out of the discourse can actually be liberating, even revolutionary — which is why Mark Thoma’s classic remark that “new economic thinking means reading old books” was so on the mark. The liquidity trap is an old idea, going back in essentially its modern form to Hicks 1937, yet people who understood it came across as radicals after 2008 — and were right.

So yes, the liberal agenda these days involves a lot of harking back to old concepts — concepts that were largely abandoned during the era of right-wing ascendancy. But those old concepts worked, whereas the “new” (now themselves quite old) ideas didn’t. Back to the future!