" To complete the reconciliation of Keynesian economics with general equilibrium theory, Paul Samuelson introduced the neoclassical synthesis in 1955...
... In this view of the world, high unemployment is a temporary phenomenon caused by the slow adjustment of money wages and money prices. In Samuelson’s vision, the economy is Keynesian in the short run, when some wages and prices are sticky. It is classical in the long run when all wages and prices have had time to adjust....
... Although Samuelson’s neoclassical synthesis was tidy, it did not have much to do with the vision of the General Theory...
... In Keynes’ vision, there is no tendency for the economy to self-correct. Left to itself, a market economy may never recover from a depression and the unemployment rate may remain too high forever. In contrast, in Samuelson’s neoclassical synthesis, unemployment causes money wages and prices to fall. As the money wage and the money price fall, aggregate demand rises and full employment is restored, even if government takes no corrective action. By slipping wage and price adjustment into his theory, Samuelson reintroduced classical ideas by the back door—a sleight of hand that did not go unnoticed by Keynes’ contemporaries in Cambridge, England. Famously, Joan Robinson referred to Samuelson’s approach as 'bastard Keynesianism.'
The New Keynesian agenda is the child of the neoclassical synthesis and, like the IS-LM model before it, New Keynesian economics inherits the mistakes of the bastard Keynesians. It misses two key Keynesian concepts: (1) there are multiple equilibrium unemployment rates and (2) beliefs are fundamental. My work brings these concepts back to center stage and integrates the Keynes of the General Theory with the microeconomics of general equilibrium theory in a new way. "
Prosperity for All: Pages 25-26