IS–LM

IS–LM
Derivative: Thomas Steiner; Islm.png: Original uploader was Vikingstad at en.wik · CC BY-SA 3.0 · source
Name	IS–LM model
Field	Macroeconomics
Introduced	1937
Creators	John Hicks, Alvin Hansen
Related	Keynesian economics, Mundell–Fleming model, Phillips curve

IS–LM

The IS–LM model is a macroeconomic tool that represents equilibrium in the Great Depression-era UK and US contexts by combining a goods-market curve and a money-market curve to analyze interactions among output, interest rates, and fiscal and monetary policy. Developed to interpret The General Theory debates among economists associated with Cambridge and Harvard, the framework became central to mid-20th-century policy discussions involving figures at institutions such as the Bretton Woods institutions, Federal Reserve, US Treasury, and national planning bodies. The model influenced policy dialogues involving leaders linked to Franklin D. Roosevelt, John Maynard Keynes, Milton Friedman, Paul Samuelson, and Robert Mundell.

Introduction

The IS–LM apparatus maps an investment–savings (IS) locus and a liquidity–money (LM) locus to determine simultaneous equilibrium in output and interest rates, a conception debated in seminars at King's College, Cambridge, Harvard, and London School of Economics. Its pedigree traces to exchanges among Keynes and commentators in the Cambridge Circus and later expositors at Columbia and Chicago. Policymakers from the New Deal and postwar cabinets in UK and US used IS–LM reasoning alongside instruments influenced by Bretton Woods arrangements and advice from economists at the IMF and World Bank.

Theoretical Framework

The IS locus represents combinations of national income and interest rates where planned expenditure equals income, a concept debated in lectures at King's College and written up by proponents including John Hicks and Alvin Hansen. The LM locus captures money-market equilibrium as discussed in policy memos at the Federal Reserve Board and academic exchanges at Princeton and MIT. IS–LM integrates elements from The General Theory, critiques from Friedrich Hayek-influenced networks, and extensions by scholars affiliated with Cowles Commission and Nobel Prize laureates. The framework interfaces with open-economy extensions such as the Mundell–Fleming synthesis advanced by Mundell and Fleming, and with labor-market constructs associated with A. W. Phillips.

Mathematical Derivation

Begin with an aggregate demand identity influenced by models taught at Harvard and LSE: output equals consumption plus investment plus government spending and net exports, with investment a decreasing function of the interest rate—assumptions discussed by Samuelson and Tobin. Money demand depends positively on income and negatively on the interest rate per analyses from Fisher and Friedman. Solving the goods-market equilibrium yields the IS curve as formalized in the early work of Hicks and popularized in textbooks by Samuelson and Mankiw. Solving the money-market equilibrium yields the LM curve following derivations used at Chicago and MIT. Intersection conditions resemble comparative-statics exercises found in papers from Cowles Foundation and policy notes by Fed New York. Extensions incorporate expectations modeled in approaches by Robert Lucas and Thomas Sargent, and stochastic generalizations employed at NBER.

Policy Implications and Applications

IS–LM provided a tractable tool for analyzing fiscal stimulus promoted by advisors in New Deal-era teams, for central-bank operations at the Federal Reserve, and for stabilization programs advocated by scholars at Brookings and CEPR. It underpins prescriptions associated with demand management promoted by Keynesian policymakers, was used to analyze exchange-rate regimes debated at Bretton Woods, and informed debates over austerity in cabinets influenced by economists from Chicago and LSE. Open-economy variants guide analysis in policy discussions at the IMF and OECD.

Criticisms and Limitations

Critiques emerged from monetarists connected to Chicago and from rational-expectations proponents such as Lucas and Sargent, who highlighted microfoundations issues debated in seminars at MIT and Princeton. Structural critiques by scholars at Cowles Commission and empirical challenges documented by researchers at NBER questioned its predictive accuracy under roofed regimes like Bretton Woods. The model's closed-economy baseline and static comparative-statics have been extended by frameworks developed at Columbia and Yale, and by dynamic stochastic general equilibrium constructs associated with Edmund Phelps.

Historical Development and Influential Contributors

Origins lie in debates after the publication of The General Theory involving figures at Kings College and LSE. Hicks distilled a compact representation in 1937 while linked to discussions across Cambridge and Oxford, and Hansen helped popularize the approach in the US through positions at Harvard and testimony to US policymaking bodies. Influential defenders and critics include Samuelson, Friedman, Tobin, Mundell, Lucas, Sargent, and policymakers at Federal Reserve and IMF. Subsequent elaborations emerged in work affiliated with Cowles Commission, NBER, and graduate programs at MIT and Princeton.

Category:Macroeconomic models