Aggregate Demand and Aggregate Supply (AD–AS Basics)

1) What is “income and output determination”?

This topic studies how the economy’s aggregate output/income (Y), employment, and price level (P) are determined.

Two common ways you’ll see it presented:

1. Keynesian income-expenditure approach (often assumes price level fixed in short run): output adjusts to demand.
2. AD–AS framework (allows price level changes): interaction of total demand and total supply.

2) Aggregate Demand (AD): meaning

Aggregate Demand is total planned spending on final goods and services in the economy.

Standard components:

Where:

• $C$: consumption expenditure by households
• $I$: investment expenditure by firms (including inventories)
• $G$: government purchases of goods and services
• $(X-M)$: net exports

2.1 AD vs “demand curve for a good”

• Demand curve for one good: relationship between price of that good and quantity demanded.
• AD curve: relationship between overall price level and total output demanded (for the whole economy).

3) Why is the AD curve downward sloping? (CUET-friendly intuition)

As the overall price level falls, quantity of goods/services demanded tends to rise due to:

1. Real balance (wealth) effect: lower prices increase real value of money balances → higher consumption.
2. Interest rate effect (in many presentations): lower prices reduce money demand → interest rates fall → investment rises.
3. Foreign trade effect: lower domestic prices make exports relatively cheaper and imports relatively expensive → net exports rise.

Hence AD typically slopes downward in $(P, Y)$ space.

4) Shifts in AD (policy and shocks)

AD shifts when any component changes at a given price level:

• $C$ rises (consumer confidence, tax cuts) → AD shifts right
• $I$ rises (lower interest rates, higher expected profits) → AD right
• $G$ rises (fiscal expansion) → AD right
• Net exports rise (foreign income rises, depreciation of currency) → AD right