Supply & Demand: How Markets Set Prices

Chapter 1 introduced scarcity and trade-offs. This chapter covers the single mechanism economists use most often to explain how those trade-offs actually get resolved in a real market: supply and demand.

The Law of Demand

All else equal, as a good's price rises, the quantity buyers are willing to purchase falls — and as price falls, quantity demanded rises. Plotted on a graph with price on the vertical axis and quantity on the horizontal, this produces a downward-sloping demand curve.

The Law of Supply

All else equal, as a good's price rises, the quantity producers are willing to sell rises too — a higher price makes production more worthwhile. This produces an upward-sloping supply curve.

Equilibrium — Where the Curves Meet

The point where the supply and demand curves cross is the market's equilibrium: the price at which the quantity buyers want to purchase exactly equals the quantity sellers want to sell. Above that price, sellers offer more than buyers want — a real surplus. Below it, buyers want more than sellers offer — a real shortage. Left alone, real market prices tend to move toward this equilibrium point.

Shifts vs. Movements

A Real, Documented Case: Price Ceilings and the 1973-74 Gas Lines

A price ceiling is a real, legally imposed maximum price — set below the market equilibrium, it creates exactly the shortage condition described above: at that lower, capped price, the quantity buyers want exceeds what sellers are willing to supply, with no price movement allowed to close the gap.

Chapter 3 builds on this directly: not every good responds to a price change by the same amount — some goods (a specific brand of soft drink) see demand collapse at a small price increase; others (petrol, insulin) barely change at all. That responsiveness has a name: elasticity.

Hands-On Exercises