2.5.4—Elasticity and surplus changes

Elastic demand or supply means quantity responds strongly to price, while inelastic curves respond weakly. Their slopes and positions affect how much consumer and producer surplus change when equilibrium moves.

A flatter demand curve can create a large quantity response and a different surplus redistribution for the same price change. Use the diagram and elasticity together rather than treating “elastic” as automatically better.

A tax on a product with inelastic demand may raise price substantially with a smaller quantity fall, shifting more burden to consumers; with elastic demand, quantity contracts more.

Elasticity predicts responsiveness, not whether surplus rises for every group; the direction of price and quantity changes must be identified first.