IS–LM model

IS–LM model
Name	IS–LM model
Field	Macroeconomics
Inventor	John Hicks
Year	1937
Based on	The General Theory of Employment, Interest and Money

IS–LM model. The IS–LM model is a foundational macroeconomic framework that depicts the interaction between the real goods market and the money market to determine equilibrium levels of interest rate and output. Developed as a graphical interpretation of John Maynard Keynes's theories, it became a central tool for analyzing the effects of fiscal policy and monetary policy. The model's equilibrium represents a short-run situation where planned spending equals income and money demand equals money supply.

Overview

The framework synthesizes Keynesian thought, providing a static, comparative tool for understanding aggregate demand. It posits two curves: the IS curve, representing equilibrium in the market for goods and services, and the LM curve, representing equilibrium in the market for money. The intersection of these curves determines the equilibrium point for the economy, a concept formalized in the work of John Hicks and later refined by Alvin Hansen. This graphical apparatus was instrumental for economists at the Massachusetts Institute of Technology and other institutions in teaching and policy debate throughout the mid-20th century.

Historical development

The model originated in 1937 with John Hicks's paper "Mr. Keynes and the 'Classics'", published in Econometrica, which aimed to reconcile Keynes's The General Theory of Employment, Interest and Money with earlier neoclassical economics. Hicks's formulation was contemporaneously developed by Alvin Hansen, leading to the widespread moniker "Hicks-Hansen synthesis". This synthesis dominated post-war macroeconomic pedagogy, notably at institutions like the London School of Economics and Harvard University, and was a cornerstone of the neoclassical synthesis that integrated Keynesian ideas with classical principles.

The IS curve

The IS curve, or Investment-Saving curve, plots all combinations of interest rates and output where total planned investment equals total saving, implying equilibrium in the goods market. Its negative slope reflects the inverse relationship between interest rates and investment spending, a relationship central to Keynesian theory. Factors shifting the IS curve include changes in government spending, taxation policies, and autonomous components of consumption and investment, as analyzed in foundational texts by economists like Paul Samuelson.

The LM curve

The LM curve, or Liquidity Preference-Money Supply curve, plots combinations of interest rates and output where the demand for real money balances equals the exogenous money supply set by the central bank, such as the Federal Reserve. Its positive slope arises because higher income increases transaction demand for money, requiring a higher interest rate to equilibrate the money market. The curve's position is influenced by changes in the nominal money supply by the Bank of England or shifts in the public's liquidity preference.

Equilibrium and policy analysis

The intersection of the IS and LM curves determines the simultaneous equilibrium in both markets, yielding a unique combination of real income and the interest rate. This framework allows for analysis of policy effects: an expansionary fiscal policy, like increased government spending, shifts the IS curve rightward, typically raising both income and interest rates. Conversely, an expansionary monetary policy by the European Central Bank shifts the LM curve rightward, lowering interest rates and stimulating income. The relative effectiveness of these policies depends on the slopes of the curves, a concept explored in the work of James Tobin and Franco Modigliani.

Criticisms and extensions

The model has faced significant criticism, particularly from the monetarist school led by Milton Friedman, who argued it neglected the role of inflation and long-run expectations. The rational expectations revolution, associated with Robert Lucas Jr., challenged its static, fixed-price assumptions. In response, economists like Robert Mundell and Marcus Fleming extended the framework to open economies, creating the Mundell–Fleming model. Later, the development of Dynamic stochastic general equilibrium models at institutions like the University of Chicago largely supplanted the IS–LM model in advanced macroeconomic research, though it remains a key pedagogical tool.

Category:Economic models Category:Macroeconomics