The General Theory of Employment, Interest, and Money

John Maynard Keynes is an English economist. It was he who laid the foundation of modern macroeconomic theory in the 1920s and 1930s.
In the "General Theory of Employment, Interest, and Money," Keynes systematically criticizes classical economic theory, examining the instability... of the capitalist system, and for the first time proves the necessity of government intervention in the economy. After the publication of his seminal work, the scholar became regarded as the founder of a new trend in economic science — Keynesianism.

"It is quite possible that the classical theory is a picture of how we would like society to function. But to assume that it actually functions this way is to ignore the real difficulties." — John Maynard Keynes