##  [IS-LM Model](/lm-model-0) 

 Definition

A short-run macroeconomic framework that determines the simultaneous equilibrium level of real output (Y) and the interest rate (r) by intersecting two reduced-form loci: the IS curve (goods market equilibrium: planned investment equals saving) and the LM curve (money market equilibrium: liquidity preference equals money supply), typically under the assumptions of a fixed price level, a closed economy, exogenous fiscal policy and an exogenous nominal money supply.

 

 

 

 

 

 





## Principle

Principle

The equilibrium (r, Y) is the intersection of IS and LM; comparative statics follow from shifts in either curve—fiscal expansion shifts IS right (tending to raise r and Y), monetary expansion shifts LM right (tending to lower r and raise Y) when prices are fixed.

 

 

 

 

 





## Demonstration

Demonstration

Illustrative scenario → Situation: A closed economy with sticky prices experiences an increase in the central bank's nominal money supply. Recognition → LM shifts right because real money balances rise at the fixed price level. Action → Interest rates fall, stimulating investment and moving output up along the IS curve. Consequence → Short-run Y increases and r falls until a new IS–LM intersection is reached.

 

 

 

 

## Misapplication

Misapplication

Treating IS-LM as a general long-run growth model or applying its comparative statics when prices are flexible, capital is perfectly mobile internationally, or money is endogenously determined; the error is using a short-run, fixed-price partial-equilibrium device as if it captured long-run price adjustment or open-economy capital flows.

 

 

 

 

 





## Consequence

Consequence

When correctly applied, the model yields transparent comparative-static predictions about how fiscal and monetary actions affect interest rates and output in the short run and clarifies mechanisms like crowding-out; misapplied, it mispredicts policy effects when key assumptions (price rigidity, closed economy, exogenous money) fail.

 

 

 

 

## Reversal

Reversal

If the economy is in a liquidity trap (LM nearly horizontal) monetary expansion has little effect on output; if prices are flexible or the economy is open with free capital mobility, the IS-LM predictions change fundamentally and require extensions (e.g., price adjustment or balance-of-payments conditions).

 

 

 

 

 





## Boundary

Boundary

Within: short-run analysis of a closed economy with sticky prices and an exogenous nominal money supply. Boundary case: partial capital mobility or slowly adjusting prices where some IS-LM intuition holds but quantitative predictions change. Outside: long-run growth, models with endogenous money, or open-economy frameworks without modifications.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Reduced-form policy comparative statics ↔ microfounded, open-economy, or general-equilibrium analyses that emphasize price adjustment, expectations, or international capital flows.

 

 

 

 

 





## Synthesis

Synthesis

IS-LM is a calibrated, short-run tool: it clarifies how contemporaneous fiscal and monetary disturbances map into r and Y under fixed prices, but it must be embedded in richer models to address price adjustment, expectations and international interactions.