Difficulty: Intermediate | Prerequisites: Supply and demand basics (Ch. 4–5)
This chapter builds on basic supply and demand to show what happens when the government steps in. If you understand how equilibrium price and quantity are set by the intersection of supply and demand, you are ready for this material. The core question: when politicians set prices by law or impose taxes, who benefits, who loses, and what unintended consequences follow? This matters because nearly every real-world market has some form of government intervention, from rent control to sales taxes to minimum wages.
Governments intervene in markets through price controls (ceilings and floors) and taxes. Price controls that bind create shortages or surpluses and lead to inefficient rationing. Taxes drive a wedge between buyer and seller prices, and the burden falls on whichever side of the market is less elastic, regardless of who the law says should pay.
Price ceiling
A legal maximum on the price at which a good can be sold. Designed to help buyers.
In simple terms, the government says "you cannot charge more than $X."
Price floor
A legal minimum on the price at which a good can be sold. Designed to help sellers.
In simple terms, the government says "you cannot pay less than $X."
Binding constraint
A price control that is actively preventing the market from reaching its equilibrium price. A ceiling below equilibrium or a floor above equilibrium is binding.
Think of it as: the rule only matters when it stops the price from going where supply and demand want it to go.
Tax incidence
The manner in which the burden of a tax is shared among participants in a market.
In simple terms, this is the answer to "who really pays the tax?" It is not necessarily the person who hands the money to the government.
Corrective tax (Pigovian tax)
A tax designed to induce private decision makers to take into account the social costs that arise from a negative externality.
Deadweight loss (preview)
The fall in total surplus that results from a market distortion such as a tax. Covered in depth in Chapter 8, but introduced here through the tax wedge.
Elasticity (in context of tax incidence)
The more elastic side of the market bears less of the tax burden; the more inelastic side bears more. This principle determines who really pays.
A price ceiling set above the equilibrium price is not binding and has no effect on the market.
A price ceiling set below the equilibrium price is binding and creates a shortage (quantity demanded exceeds quantity supplied).
When a binding ceiling is in place, the market price equals the ceiling price, not the equilibrium price.
Sellers must ration the scarce good among buyers. Rationing mechanisms include long queues (inefficient, wastes time) and seller discrimination (biased, based on personal preferences such as race, family ties, or friendships).
By contrast, free markets ration goods with prices, which is both efficient and impersonal.
OPEC reduced crude oil production, shifting the supply curve for gasoline leftward.
The U.S. government had regulations capping gasoline prices. Before the supply shock, the ceiling was above equilibrium (not binding). After the shift, the ceiling became binding.
Result: severe shortage, long queues at petrol stations.
Economists blame the government ceiling, not just OPEC, for the queues.
Rent control is a price ceiling on housing rents, intended to help the poor afford housing.
Short run: both supply and demand for housing are relatively inelastic. The shortage is small, and the primary result is a reduction in rents for existing tenants.
Long run: supply and demand become more elastic. Landlords stop building new apartments and let existing ones deteriorate. More people seek their own flats. The shortage grows much larger.
Landlords ration housing through waiting lists, discrimination, or preference for tenants without children.
Economists widely regard rent control as a highly inefficient way to help the poor. Alternatives include housing subsidies that do not distort the market.
A price floor set below the equilibrium price is not binding and has no effect.
A price floor set above the equilibrium price is binding and creates a surplus (quantity supplied exceeds quantity demanded).
Sellers who can appeal to buyers' personal biases may sell more easily; in a free market, the price itself serves as the rationing mechanism.
The minimum wage is a price floor in the labour market. Workers supply labour; firms demand it.
A binding minimum wage causes a surplus of labour, which is unemployment.
It raises the incomes of workers who keep their jobs but lowers the incomes of those who cannot find work.
The impact depends on skill level: highly skilled workers earn well above the minimum, so for them it is not binding. The minimum wage is most binding for teenagers and low-skill workers.
Most studies focus on short-run effects; longer-term effects on employment are harder to estimate but more relevant for evaluating the policy.
Prices have the crucial job of balancing supply and demand and coordinating economic activity. When policymakers set prices by law, they obscure the signals that normally guide the allocation of resources.
Alternative policies that work with the market rather than against it: rent subsidies for poor families, wage subsidies for the working poor.
A tax on sellers raises the cost of production, shifting the supply curve upward (leftward) by the size of the tax.
The demand curve does not change.
In the new equilibrium, the market price rises (buyers pay more) and the equilibrium quantity falls.
Example: a $0.50 tax on ice cream sellers shifts supply up by $0.50. Price rises from $3.00 to $3.30. Sellers receive $3.30 from buyers but keep only $2.80 after paying the tax. Quantity falls from 100 to 90.
Although sellers send the entire tax to the government, buyers and sellers share the burden. Buyers pay $0.30 more per unit; sellers receive $0.20 less per unit.
A tax on buyers shifts the demand curve downward (leftward) by the size of the tax.
The supply curve does not change.
In the new equilibrium, the market price falls and the equilibrium quantity falls.
Example: a $0.50 tax on ice cream buyers. Price falls from $3.00 to $2.80. Buyers pay $2.80 to sellers plus $0.50 to the government, so their effective price is $3.30. Quantity falls from 100 to 90.
The outcome is equivalent to a tax on sellers of the same size. The split of the burden is the same.
A $1 per-unit tax levied on consumers of a good is equivalent to a $1 per-unit tax levied on producers of the good. The statutory incidence (who writes the cheque) does not determine the economic incidence (who bears the burden).
FICA (payroll tax) is split by law: half paid by employers, half deducted from workers' pay.
The tax places a wedge between the wage firms pay and the wage workers receive.
Workers and firms share the burden based on the elasticities of labour supply and demand, not on the legislated 50/50 split.
The tax burden falls more heavily on the side of the market that is less elastic.
Elastic supply, inelastic demand: buyers bear most of the burden (the price they pay rises by nearly the full tax; the price sellers receive falls only a little).
Inelastic supply, elastic demand: sellers bear most of the burden (the price buyers pay rises little; the price sellers receive falls substantially).
In the early 1990s, the U.S. placed a luxury tax on yachts, private aeroplanes, and expensive cars, aiming to raise revenue from the wealthy.
Luxury goods have elastic demand (they are easy to avoid buying).
The supply of these goods is relatively inelastic (the workers and firms that build them cannot easily switch industries).
Result: the burden fell largely on the firms and workers who build luxury goods (middle-class), not on the wealthy buyers. The tax was eventually repealed.
Shortage = Quantity demanded - Quantity supplied (when a binding price ceiling holds the price below equilibrium)
Surplus = Quantity supplied - Quantity demanded (when a binding price floor holds the price above equilibrium)
Tax wedge = Price buyers pay - Price sellers receive = Size of the tax
Government tax revenue = Tax per unit x Quantity sold
Tax burden on buyers = New price buyers pay - Old equilibrium price
Tax burden on sellers = Old equilibrium price - New price sellers receive
Key diagrams to know (refer to Mankiw 9e, Chapter 6):
Binding vs. non-binding price ceiling (supply-demand with horizontal ceiling line)
Binding vs. non-binding price floor (supply-demand with horizontal floor line)
Tax on sellers shifting the supply curve upward by the tax amount
Tax on buyers shifting the demand curve downward by the tax amount
Elastic supply/inelastic demand vs. inelastic supply/elastic demand panels showing how elasticity determines tax incidence
Rent control is the textbook example of a price ceiling. Cities such as New York and San Francisco have used it for decades, and the long-run housing shortages that result are exactly what the model predicts: deteriorating buildings, long waiting lists, and landlord discrimination.
Minimum wage laws are a price floor in the labour market. The debate over raising the minimum wage is essentially a debate about the elasticity of labour demand: if demand is inelastic, higher wages help more workers than they hurt; if demand is elastic, job losses are significant.
Sales taxes and VAT are examples of per-unit taxes. The tax-incidence framework explains why, for instance, a tax on petrol is borne largely by consumers (inelastic demand for fuel) rather than by oil companies.
The luxury tax episode shows that a tax intended for the rich can end up hurting middle-class workers when demand is elastic and supply is inelastic.
"The person who pays the tax to the government bears the burden." Wrong. Tax incidence depends on elasticities, not on who writes the cheque. A tax on sellers is economically equivalent to a tax on buyers of the same size.
"Price ceilings always cause shortages." Only binding ceilings (set below equilibrium) cause shortages. A ceiling above equilibrium has no effect.
"Rent control helps all renters." In the short run it lowers rents for those who have flats, but in the long run it reduces housing quality and quantity, making the overall housing situation worse.
"The minimum wage only helps workers." It helps workers who keep their jobs at the higher wage, but it harms those who lose their jobs or cannot find one. The net effect depends on the elasticity of labour demand.
⚠️ Know the difference between binding and non-binding price controls. The exam will give you a ceiling or floor price and an equilibrium price and ask you to determine which case applies.
⚠️ Be able to show graphically how a tax shifts the supply curve (tax on sellers) or demand curve (tax on buyers) and identify the new equilibrium price and quantity.
⚠️ Understand that the statutory incidence (who is legally required to pay) does not determine the economic incidence (who bears the burden). This is a commonly tested principle.
⚠️ Know that the burden of a tax falls on the less elastic side of the market. Be prepared to explain why with reference to specific examples.
⚠️ Rent control: be able to explain why effects are different in the short run vs. the long run (elasticity changes over time).
⚠️ An increase in the minimum wage reduces total payments to affected workers if the price elasticity of demand for labour is greater than one.
True or False: A price ceiling set above the equilibrium price will cause a shortage. (False: it is not binding.)
True or False: A tax on buyers and a tax on sellers of the same amount produce different market outcomes. (False: the outcomes are equivalent.)
Fill in the blank: A binding price floor causes a ______. (Surplus.)
True or False: Rent control causes larger shortages in the long run than in the short run. (True: supply and demand are more elastic over time.)
Fill in the blank: The tax burden falls more heavily on the ______ side of the market. (Less elastic.)
Q: When the government imposes a binding price floor, what happens in the market?
A: A surplus of the good develops. Quantity supplied exceeds quantity demanded at the floor price.
Q: In a market with a binding price ceiling, what is the effect of increasing the ceiling price (while keeping it below equilibrium)?
A: The shortage decreases. The gap between quantity demanded and quantity supplied narrows as the ceiling moves closer to equilibrium.
Q: A $1 per-unit tax is levied on consumers of a good. What is this equivalent to?
A: A $1 per-unit tax levied on producers of the good. The economic outcome (price paid by buyers, price received by sellers, quantity) is the same regardless of which side the tax is levied on.
Q: When a good is taxed, under what conditions does the burden of the tax fall mainly on consumers?
A: When supply is elastic and demand is inelastic. Consumers cannot easily reduce their purchases, so they absorb most of the price increase.
Q: Why does rent control cause larger shortages in the long run than in the short run?
A: Over time, supply and demand become more elastic. Landlords stop building and maintaining rental housing (supply becomes more elastic), and more people seek their own housing at the low controlled rent (demand becomes more elastic). Both effects widen the shortage.
Q: An increase in the minimum wage reduces total payments to affected workers under what condition?
A: When the price elasticity of demand for labour is greater than one. The percentage fall in employment exceeds the percentage rise in the wage, so total payments (wage x quantity of labour) decline.
This material connects directly to Chapter 5 (Elasticity), since the relative elasticities of supply and demand determine tax incidence and the severity of shortages and surpluses under price controls. It also leads into Chapter 7 (Consumer and Producer Surplus) and Chapter 8 (Costs of Taxation), where the welfare effects of taxes are measured precisely using deadweight loss. The minimum-wage discussion previews labour-market topics that appear later in the course.
Related Terms / Search Tags
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