Think about it: In the 1930s you had a catastrophe, and if you were a public official or even just a layman looking for guidance and understanding, what did you get from institutionalists? Caricaturing, but only slightly, you got long, elliptical explanations that it all had deep historical roots and clearly there was no quick fix. Meanwhile, along came the Keynesians, who were model-oriented, and who basically said “Push this button”– increase G, and all will be well. And the experience of the wartime boom seemed to demonstrate that demand-side expansion did indeed work the way the Keynesians said it did.
It’s not an accident that Samuelson, even as he was raising the math level of microeconomics, was a key figure in the triumph of Keynesian economics. Nor was it at all an accident that his intro textbook, in its 1948 edition and for a long time thereafter, started with macro, and only got to micro later. The perceived success of macroeconomics did double duty, establishing the bona fides of a model-oriented approach and also suggesting that full employment was not too bad an assumption — given the right monetary and fiscal policies.
Once you have involuntary unemployment, [market optimality] fails. Keynes’ famous thought experiment of burying pound notes in coal mines made the point that an intervention that would be totally absurd in terms of standard microeconomic reasoning might nonetheless help to alleviate a recession and therefore make society better off…. None of the standard conclusions of… microeconomics can be assumed to be valid under conditions of sustained high unemployment. Keynes specifically presented his macroeconomic ideas as making the world safe for neoclassical micro. If governments could stabilise the aggregate economy with fiscal policy, there was no need for comprehensive economic planning of the kind being practised, with apparent success, in the Soviet Union, or for ad hoc interventions like the price-fixing elements of the New Deal…. The failure of macroeconomists and finance economists to provide either a warning of the Global Financial Crisis or any consistent advice on how to deal with the ensuing Great Recession it isn’t just a problem for them. It undermines the whole economics profession. The sooner we realise that the entire discipline is in a state of scientific crisis the sooner we might start to do something about it.