At the intersection, a single income-interest-rate pair satisfies both equilibrium conditions at once: planned spending equals output, and real money demand equals the available money supply. This matters because analyzing either market separately could produce a condition that fails in the other. The intersection therefore provides the model’s joint short-run equilibrium for evaluating policy effects.
The IS curve links goods-market equilibrium to the spending decisions that determine output, while the LM curve links money-market equilibrium to real money demand and the available money supply. A policy change can alter one of these relationships, moving the intersection and changing both income and interest rates. The model thus connects separate market adjustments in one framework.
An increase or decrease in government spending or taxes is examined as a fiscal-policy change affecting the goods-market side of the model. The resulting movement in the IS-LM diagram indicates the associated changes in equilibrium national income and interest rates. It also helps assess consequences for investment and whether fiscal action supports short-run economic stabilization.
Changes in the money supply are represented as monetary-policy adjustments affecting the money-market side of the framework. By locating the new intersection of the IS and LM curves, analysts can trace the implied change in national income and the interest rate. This provides a structured way to study monetary influence on output and stabilization.
To apply the model, identify the planned-spending condition for the IS curve and the real-money-demand condition for the LM curve. Then locate their intersection, introduce a fiscal or monetary policy change, and examine the new intersection. Comparing the original and revised positions reveals the predicted changes in output, interest rates, investment, and stabilization.
Fiscal and monetary policy enter the framework through different market conditions. Government spending and taxes are analyzed through their effects on the goods-market relationship, whereas money-supply changes are analyzed through the money-market relationship. Comparing the two policy changes within the same diagram helps distinguish their predicted effects on national income and interest rates.
Macroeconomists use the IS-LM model when they need to assess short-run policy effects on the overall economy rather than examine goods or money markets in isolation. It supports analysis of output, interest rates, investment, and stabilization under alternative fiscal and monetary measures. Its value lies in organizing these linked outcomes around one equilibrium framework.