Law of Demand

What Is Law of Demand?

The law of demand is the foundational rule that, holding everything else constant, the quantity of a good consumers wish to buy moves inversely to its price: when price rises, quantity demanded falls, and when price falls, quantity demanded rises. This inverse relationship is why the demand curve slopes downward. Crucially, a change in the good's own price produces a movement along the existing demand curve, not a shift of the curve itself. Shifts come only from non-price determinants. The law reflects two forces: as price rises, buyers substitute toward cheaper alternatives, and their real purchasing power falls.

Why It Matters

The law of demand is one of the most reliable regularities in economics and anchors nearly every market analysis. It explains why sales raise the quantity sold and why shortages emerge when prices are held artificially low. Because the relationship is predictable, businesses and policymakers use it to anticipate how buyers respond to price changes, which is the basis of the price elasticity of demand that measures the size of that response. The law also clarifies a common error: a bad harvest does not violate it. Higher prices from reduced supply move buyers up along a fixed demand curve; the curve itself only shifts when tastes, income, related-good prices, expectations, or the number of buyers change.