Supply, Demand, and Market Equilibrium
The Law of Demand shows an inverse relationship between price and quantity - when prices go up, people buy less. Remember, demand means being both willing AND able to purchase something. For example, Mr. Stirn might be able to afford milk but isn't willing to buy it because he's lactose intolerant.
Only price changes move us along the demand curve. Meanwhile, the Law of Supply shows a direct relationship between price and quantity - when prices rise, producers supply more. Five key factors can shift the entire demand curve: taste preferences, related goods, income levels, number of buyers, and expectations of future prices.
Supply curves shift due to six factors: resource costs, other outputs, technology improvements, taxes and subsidies, expectations, and number of suppliers. When both supply and demand shift simultaneously, either the new price or quantity must be indeterminate - we call this the Double Shift Rule.
Real-world connection: Price controls are government tools that manipulate market prices. Price ceilings (maximum prices) set below equilibrium create shortages - think of rent control in expensive cities where apartments become scarce!