John M. Keynes is the world-famous author of The General Theory of Employment, Interest and Money, published in 1936.

In Keynes’s theory, macro-level trends can overwhelm the micro-level behavior of individuals. Instead of the economic process being based on continuous improvements in potential output, Keynes asserted the importance of the aggregate demand for goods as the driving factor. He argued that government policies could be used to promote demand at a macro level, and to fight unemployment and deflation.

Keynes stated that there was no strong automatic tendency for output and employment to move toward full employment levels. This conflicts with the principles of classical economics, and the supply-side economics, which assume a general tendency towards equilibrium in a restrained money creation economy.

Keynes questioned two of the dominant pillars of economic theory: the need for a gold standard, and the Say’s Law which stated that decreases in demand would only cause price declines, rather than affecting real output and employment.

It was his experience with the Treaty of Versailles that pushed him to break with previous theory. His book The Economic Consequences of the Peace (1920) recounted the general economics of the Treaty and the individuals involved in making it. The book established him as an economist who had the practical skills to influence policymakers. Keynes developed the idea of monetary policy as something separate from maintaining currency against a fixed peg. He believed that economic systems would not automatically right themselves to attain «the optimal level of production». He used to say «In the long run, we are all dead,» implying that it doesn’t matter that optimal production levels are attained in the long run, because it’ll be a very long run indeed.

In the late 1920s, the world economic system began to break down, after the shaky recovery that followed World War I. Critics of the gold standard, market self-correction, and production-driven paradigms of economics moved to the fore. Dozens of different schools contended for influence. Some pointed to the USSR as a successful centrally-planned economy; others pointed to the alleged success of fascism in Italy.

Keynes stepped into this chaos and promised not to institute revolution but to save capitalism. He circulated a simple thesis: there were more factories and transportation networks than could be used at the current ability of individuals to pay and the problem was on the demand side.