Broadly speaking, [Keynesianism means] that the government has a specific responsibility for the behavior of the economy, that it doesn't work on its own autonomous course, but the government, when there's a recession, compensates by employment, by expansion of purchasing power, and in boom times corrects by being a restraining force. But it controls the great flow of demand into the economy, what since Keynesian times has been the flow of aggregate demand. That was the basic idea of Keynes so far as one can put it in a couple of sentences.

Booknotes interview (1994)