The Basics of Demand and Supply

Welcome to the foundation of microeconomics. While Macroeconomics looks at the big picture, this chapter focuses on the individual "market mechanism" that determines the prices of everything from a cup of coffee to a high-end graphics card.

1. The Law of Demand: The Consumer’s Perspective

Demand is the amount of a product consumers are willing and able to purchase at various prices.

• The Law: There is an inverse relationship between price and quantity demanded.
  • As Price Increases, Quantity Demanded Decreases.
  • As Price Decreases, Quantity Demanded Increases.
• The Curve: Because of this inverse relationship, the demand curve is always downward-sloping.
• Ceteris Paribus: This law assumes "all other things being equal". If other factors (like your income) change, the entire curve shifts.

1. The Law of Supply: The Producer’s Perspective

Supply is the quantity of a product that firms are willing to offer to the market at a given price.

• The Law: There is a direct relationship between price and quantity supplied.
  • As Price Increases, Quantity Supplied Increases (due to the profit motive).
  • As Price Decreases, Quantity Supplied Decreases.
• The Curve: The supply curve is upward-sloping, reflecting that producers want to sell more at higher prices.

1. Market Equilibrium: The "Sweet Spot"

The market price is determined where these two forces meet.

• Equilibrium Point: This occurs at the intersection of the demand and supply curves.
• Market Clearing: At this point, the quantity consumers want to buy exactly matches the quantity producers want to sell.
• Surplus vs. Shortage:
  • Surplus: If price is above equilibrium, supply exceeds demand.
  • Shortage: If price is below equilibrium, demand exceeds supply.

4. Shifts vs. Movements

It is critical to distinguish between a change in quantity and a change in demand/supply itself.

• Movements Along the Curve: Caused only by a change in the product's own price.
• Shifts of the Entire Curve: Caused by "non-price" factors.
  • Demand Shifters: Changes in consumer income, tastes, population size, or the price of related goods (substitutes and complements).
  • Supply Shifters: Changes in production costs (raw materials, labor), technology, number of sellers, or government taxes/subsidies.

Summary Table: Demand vs. Supply