Born in 1883 and dying in 1946, the bulk of Keynes's professional life was framed by two world wars. At the beginning, he was an Edwardian optimist, … - Robert Skidelsky

The General Theory of Employment, Interest and Money is a work of enduring fascination. It is simple and subtle, obscure and profound. It offered a systematic way of thinking not just about the behaviour of contemporary economies, but about the pitfalls in the quest for greater wealth at all times. It combined a vision of the future with a rigorous demonstration of the possibility of underemployment equilibrium. Although young economists of speculative bent were drawn to it as a storehouse of suggestive ideas, it was its practical usefulness which chiefly attracted them in a world poised between decaying democracy and rampaging dictatorship.
At its core is a 'theory of output and employment as a whole', to distinguish it from the orthodox theory of what causes 'the rewards and distribution between different uses of a given quantity of resources' to be what they are. Keynes was the first economist to visualise the economy as an aggregate quantity of output resulting from an aggregate stream of expenditure. This new way of seeing the architecture of an economy is the General Theory's most enduring legacy.

Keynes's idea was very simple. Monetary and fiscal policy should have a single goal, jointly pursued, of maintaining a full employment level aggregate demand.

The reason why economics has given such a poor account of the origins of the crisis is that there is something essentially incompatible between the economist's view of individual rationality and systemic collapse. Without adding qualifications which strain their logic, economists cannot readily get from their picture of the the individual maximizing his utilities to booms and slumps and the persistence of depressions.