The article looks at how economic theories have changed over time, starting with the Great Depression. It discusses the Classical Economic Theory and its problems, then moves on to Keynesianism and the benefits of fiscal policy. The paper also talks about the Phillips Curve and the effects of monetary policy in the 1970s and the 2008 recession. Modern economists like Friedman believe we should use both Keynesianism and Monetarism in today's economy, using fiscal policy during downturns and monetary policy during economic booms.