Keynes’s original idea was to concentrate on public works and infrastructure, on expenditure intended to orient production and not on unproductive expenditure, although he later used the paradox of digging holes in the ground and then filling them in to explain the principle of effective demand. On the theoretical level, the Keynesian model is definitively established as an explanation of how an economy works.
I was brought up on Keynesian theory by Modigliani and Samuelson at the Massachusetts Institute of Technology in the 1960s. Solow’s classes introduced me to the theory of growth. Those were the years of Kennedy’s New Frontier and the new economic policy.