The economic environment emphasized by Keynes is different from the economic environment emphasized by Say. Say emphasized that the purpose of supply is demand, but Keynes emphasized effective demand. He believes that national income is mainly restricted by the level of demand, and market adjustment mechanisms alone are not enough to achieve equilibrium in the economy. To this end, government intervention is necessary to fill the effective demand gap in society, that is, to achieve full employment equilibrium.

In the short term, I will be more accepting of Keynesianism. Often effective demand can promote short-term consumption. But in the long run, effective demand fluctuates greatly and consumption cannot be measured specifically. Say's "supply creates its own demand" can well reflect the long-term economic environment, and supply determines consumption.

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John Maynard Keynes (June 5, 1883 - April 21, 1946), British economist, modern economics One of the most influential economists, the macroeconomics he founded, the psychoanalysis created by Freud and the theory of relativity discovered by Einstein are known as the three major revolutions in human knowledge in the twentieth century.

In 1936, Keynes's masterpiece "The General Theory of Employment, Interest and Money" ("The General Theory") was published. His other two important economic theory works are A Tract on Monetary Reform (1923) and A Treatise on Money (1930).

Keynes is famous for creating the "Keynesian Revolution" in economics and is called the "Father of Macroeconomics" by future generations.