The blogospheric debate about microfoundations, saltwater/freshwater and all that has, I think, been illuminating. Among other things it’s serving almost as an oral history of What Really Happened – minus the oral part, but not mediated by the usual slowness and overthinking of formal publication.

And I think the intellectual history is useful, because it gives you some idea of how people came to make the choice of which side to be on. It’s certainly possible to make the case for an eclectic, fairly salty approach on general principles, as Simon Wren-Lewis, Noah Smith, and Nick Rowe do. But the abstract logic gains force when you recall how it actually happened.

Oh, and I was there – not as a participant in the growing macro war, but as a student at the time the great divide was taking place. I felt the seduction of the microfoundations-uber-alles doctrine, but also got to watch as the demand for microfoundations, originally grounded in appeals to empirical power, became free-floating, a dogma to be defended in the teeth of the evidence.

So, if you had to choose a beginning, it would be the famous Phelps volume. The papers in that volume all started with two observations, of which the first was that there was overwhelming evidence for some kind of short-run non-neutrality of money. None of the papers in that volume questioned the proposition that nominal shocks had large real effects. You can see why if you look at annual changes in nominal versus real GDP between 1950 and 1970:

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Obviously there was a near one-to-one correspondence. Obviously, too, it was really hard in that era, with its lack of major supply shocks, to tell a story in which real GDP was driving nominal spending rather than vice versa. So the Phelps volume began with the stylized fact that in the short run nominal demand, driven for example by changes in monetary policy, gets reflected largely in quantities rather than prices.

But as the papers also observed, it was hard to explain that fact in terms of standard microeconomics: with everyone acting rationally, money should have been neutral even in the short run. Traditional Keynesian analyses simply said that people aren’t completely rational, that they have money illusion – or maybe that contracts are focal points in which nominal wages or prices matter because of salience, even though they should be arbitrary. But these were ex post rationalizations rather than being derived from some kind of fundamentals.

So the Phelps crowd came up with a lovely story: you see, it was all about information. Individuals and firms couldn’t tell, in the very short run, whether a rise in the price they were being offered represented a shock specific to them – people for some reason wanted more of their widgets — or a general change in demand. It was rational to respond to an idiosyncratic rise in demand by producing more, so confusion could explain why short-run aggregate supply seemed upward-sloping.

As Phelps and others (including Milton Friedman, who was thinking along similar lines) realized, this meant that the apparent tradeoff between unemployment and inflation would be unstable: sustained inflation would get built into expectations, and would no longer produce low unemployment. The stagflation of the 70s seemed to confirm this prediction, and brought the microfoundations project immense prestige. Encouraged by all this, freshwater economists gleefully proclaimed Keynes dead, the subject of nothing but “giggles and whispers”.

But here’s the thing: after that initial success, Phelps-Lucas/type microfoundations quickly collapsed both intellectually and empirically. Intellectually, the problem was that rational individuals simply should not have been confused in the way the models demanded; there’s too much information out there, whether in newspapers or in asset prices. You just couldn’t get a Lucas supply curve out of a model looking even vaguely like the real economy.

Empirically, the problem was that slumps last too long. Even if you wave away the information problem, confusion about aggregate versus idiosyncratic shocks can last for quarters, maybe, but not years.

So the truth was that microfoundations in macroeconomics had its moment, but failed utterly at the one thing it was sold, above all, as being able to do – namely, give a better explanation of why nominal shocks have real effects. Time, you might think, to reconsider the project.

And some did. There was a revival of Keynesian thinking in the late 70s and early 80s, albeit one that tried to cram as many microfoundations into the models as possible without being grossly unrealistic.

But many economists had so committed themselves to the idea that Keynes was dead and rationality roolz that they simply dug in deeper. Rationality-based microfoundations must be right; if their microfoundations couldn’t explain why nominal shocks have real effects, then nominal shocks must not have real effects – it’s all real shocks. And so real business cycle theory was born.

So now we have people debating whether models with microfoundations lead to better predictions, both of the future and of policy impacts, than models with ad hoc elements; as Wren-Lewis and Smith say, this is by no means obvious if the microfoundations are wrong, as they often clearly are. But what you want to realize is that this isn’t going to convince the microfoundations crowd. After all, more than thirty years ago they decided that the joy of microfoundations trumped the utter failure of microfounded models to work in practice, and they have now trained successive cohorts of students in this view.

There are, it’s true, some hints of a guilty conscience – as Matt Yglesias points out, there’s the odd tendency of freshwater types to immediately accuse anyone with saltwater ideas of being dishonest. (I’m not a nice guy, but if look at what I said about, say, Cochrane, it was that he was ignorant, not corrupt.)

Oh, and the notion that there had been a convergence of views by 2007, which was then ruptured by the crisis, was a saltwater delusion. People like Olivier Blanchard convinced themselves that the other side was listening; it wasn’t. The hysterical reaction to the notion that fiscal policy is effective at the zero lower bound demonstrated that the freshwater types had never bothered to learn the least thing about how New Keynesian models worked.

So there’s a lot of history here; but the main driver behind this history was, I believe, the inability of many economists to accept the fact that they took a wrong turn.