Brad DeLong points me to Lars Syll declaring that I am not a “real Keynesian”, because I use equilibrium models and don’t emphasize the instability of expectations.

One way to answer this is to point out that Keynes said a lot of things, not all consistent with each other. (The same is true for all of us.) Right at the beginning of the General Theory, Keynes explains the “ principle of effective demand” with a little model of temporary equilibrium that takes expectations as given. If that kind of modeling is anti-Keynesian, the man himself must be excommunicated.

But surely we don’t want to do economics via textual analysis of the masters. The questions one should ask about any economic approach are whether it helps us understand what’s going on, and whether it provides useful guidance for decisions.

So I don’t care whether Hicksian IS-LM is Keynesian in the sense that Keynes himself would have approved of it, and neither should you. What you should ask is whether that approach has proved useful — and whether the critics have something better to offer.

And as I have often argued, these past 6 or 7 years have in fact been a triumph for IS-LM. Those of us using IS-LM made predictions about the quiescence of interest rates and inflation that were ridiculed by many on the right, but have been completely borne out in practice. We also predicted much bigger adverse effects from austerity than usual because of the zero lower bound, and that has also come true.

Now, what have those who declare themselves the true Keynesians had to offer? Has insisting that expectations are volatile and unpredictable been helpful in this context? Actually, if anything it lends support to believers in the confidence fairy. After all, if it’s all animal spirits, who are we to say they’re wrong?

Has declaring uncertainty to be unquantifiable, and mathematical modeling in any form foolish, been productive? Remember, that’s what the Austrians say too.

If you can show me any useful advice given by those sniping at me and other for our failure to be proper Keynesians, I’ll be happy to take it under consideration. If you can’t, then we’re just doing literary criticism here, and I’m not interested.