According to the real business cycle model (a.k.a: 'freshwater', rational expectations, new classical...), fiscal and monetary policy are impotent to fight recessions because...
...if people do know that there’s a recession, they know that the low prices they’re being offered reflect low overall demand, not specifically low demand for their products.
In Lucas-type models, people were supposed to look at the prices they received, and optimally extract the “signal” from the “noise”. The models broke down, however, as soon as you let people have access to any other information – say, by looking at interest rates, or reading a newspaper. And the reality, of course, is that recessions persist long after everyone knows that there’s a recession, so that the confusion required by Lucas-type models is long since gone.
I recall a seminar, I think in 1980, in which Robert Barro was presenting a rational-expectations business cycle model. Someone asked him how he could reconcile his model with the severe recession taking place as he spoke. “I’m not interested in the latest residual,” Barro snapped.
But by 1980 or 1981 it was basically clear to everyone that the Lucas project – the attempt to explain the evidently Keynesian behavior of the economy in terms of nothing but imperfect information – had failed. So what were macroeconomic theorists supposed to do?
The answer was that they split. One faction said, in effect, “OK: we can’t explain what we think we see in terms of full maximization. So we have to assume that there are some limits to maximization – costs of changing prices, bounded rationality, whatever.” That faction became New Keynesian, saltwater economics.
The other faction said, in effect, “OK: we can’t explain what we think we see in terms of full maximization. So we must be interpreting the data wrong – things like changes in the money supply must not be driving recessions, because theory says they can’t.” That faction became real business cycle, freshwater economics.
But here’s the thing: at this point, the freshwater school no longer remembers any of that – largely because they purged Keynesian and even monetarist thought from their classes. All they know is that Keynesianism was “disproved”, and that none of it – not even New Keynesian models with rational expectations (an approach which, as Greg Mankiw says, “provides a rationale for government intervention in the economy, such as countercyclical monetary or FISCAL POLICY.”) – is worth listening to.
So that’s how we got to where we are today.
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