A macroeconomic theory based on the ideas of 20th-century British economist John Maynard Keynes. Keynesian economics argues that private sector decisions sometimes lead to inefficient macroeconomic outcomes and therefore advocates active policy responses by the public sector, including monetary policy actions by the central bank and fiscal policy actions by the government to stabilize output over the business cycle. The theories forming the basis of Keynesian economics were first presented in The General Theory of Employment, Interest and Money, published in 1936; the interpretations of Keynes are contentious, and several schools of thought claim his legacy.
Keynesian economics advocates a mixed economy—predominantly private sector, but with a large role of government and public sector—and served as the economic model during the latter part of the Great Depression, World War II, and the post-war Golden Age of Capitalism, 1945–1973, though it lost some influence following the stagflation of the 1970s. As a middle way between laissez-faire capitalism and socialism, it has been and continues to be attacked from both the right and the left. The advent of the global financial crisis in 2007 has caused a resurgence in Keynesian thought. Keynesian economics has provided the theoretical underpinning for the plans of President Barack Obama, Prime Minister Gordon Brown and other global leaders to rescue the world economy.
In Keynes's theory, there are some micro-level actions of individuals and firms that can lead to aggregate macroeconomic outcomes in which the economy operates below its potential output and growth. Some classical economists had believed in Say's Law, that supply creates its own demand, so that a "general glut" would therefore be impossible. Keynes contended that aggregate demand for goods might be insufficient during economic downturns, leading to unnecessarily high unemployment and losses of potential output. Keynes argued that government policies could be used to increase aggregate demand, thus increasing economic activity and reducing unemployment and deflation.
Keynes argued that the solution to depression was to stimulate the economy ("inducement to invest") through some combination of two approaches: a reduction in interest rates and government investment in infrastructure. Investment by government injects income, which results in more spending in the general economy, which in turn stimulates more production and investment involving still more income and spending and so forth. The initial stimulation starts a cascade of events, whose total increase in economic activity is a multiple of the original investment.
A central conclusion of Keynesian economics is that, in some situations, no strong automatic mechanism moves output and employment towards full employment levels. This conclusion conflicts with economic approaches that assume a general tendency towards an equilibrium. In the 'neoclassical synthesis', which combines Keynesian macro concepts with a micro foundation, the conditions of general equilibrium allow for price adjustment to achieve this goal.
The new classical macroeconomics movement, which began in the late 1960s and early 1970s, criticized Keynesian theories, while New Keynesian economics have sought to base Keynes's idea on more rigorous theoretical foundations.
More broadly, Keynes saw this as a general theory, in which utilization of resources could be high or low, whereas previous economics focused on the particular case of full utilization.
Some interpretations of Keynes have emphasized his stress on the international coordination of Keynesian policies, the need for international economic institutions, and the ways in which economic forces could lead to war or could promote peace.