1. 15 Monopoly P R I N C I P L E S O F F O U R T H E D I T I O N
The most important concept in this chapter is the relation between MR and P for a monopolist. Everything else in the chapter – markup pricing, economic profit, deadweight loss, public policy response, etc – all flow from the relationship between P and MR.
This relationship is also important because P > MR for firms with market power in other market structures, such as monopolistically competitive firms. Since P > MR for these firms, many of the same issues arise.
For most students, the relationship between P and MR is the most challenging topic in the chapter. This PowerPoint includes an Active Learning exercise requiring students to calculate marginal revenue at various quantities from a demand schedule, so students will see for themselves that MR < P. The PowerPoint also includes careful explanation on the relation between MR and P. I hope your students find it helpful.
Another tricky concept for some students is identifying the monopolist’s price on a graph. Students generally can find the profit-maximizing quantity, where the MR and MC curves intersect. But they sometimes forget to go up to the D curve to find the highest price the market will bear at that quantity.

2. In this chapter, look for the answers to these questions:
Why do monopolies arise?
Why is MR < P for a monopolist?
How do monopolies choose their P and Q?
How do monopolies affect society’s well-being?
What can the government do about monopolies?
What is price discrimination?
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3. Introduction
A monopoly is a firm that is the sole seller of a product without close substitutes.
In this chapter, we study monopoly and contrast it with perfect competition.
The key difference: A monopoly firm has market power, the ability to influence the market price of the product it sells. A competitive firm has no market power.
Most students already know that monopoly means the firm is the only seller of its product. But the definition here has another very important part: In order for the firm to be considered a monopoly, the product it sells must have no close substitutes available from other firms.
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4. Why Monopolies Arise
The main cause of monopolies is barriers to entry – other firms cannot enter the market.
Three sources of barriers to entry:
1. A single firm owns a key resource.
E.g., DeBeers owns most of the world’s diamond mines
2. The govt gives a single firm the exclusive right to produce the good.
E.g., patents, copyright laws
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5. Why Monopolies Arise
3. Natural monopoly: a single firm can produce the entire market Q at lower ATC than could several firms.
Example: homes need electricity.
Electricity Q
Cost
ATC
Economies of scale due to huge FC
ATC is lower if one firm services all 1000 homes than if two firms each service 500 homes.
The horizontal axis of the graph measures number of homes provided electricity. The vertical axis measures the average total cost of providing electricity per home.
500
$80
1000
$50
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6. Monopoly vs. Competition: Demand Curves
In a competitive market, the market demand curve slopes downward.
but the demand curve for any individual firm’s product is horizontal at the market price.
The firm can increase Q without lowering P,
so MR = P for the competitive firm.
A competitive firm’s demand curve P Q
A competitive firm is a price-taker, can sell as much as it wants at the market price.
In effect, the competitive firm sells a product for which there are many perfect substitutes, so demand for its product is perfectly elastic; if it raises its price above the market price, demand for its product falls to zero.
The relationship between P and MR is what distinguishes a competitive firm from a monopoly firm, in terms of both firm behavior and welfare implications. D
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7. Monopoly vs. Competition: Demand Curves
A monopolist is the only seller, so it faces the market demand curve.
To sell a larger Q, the firm must reduce P.
Thus, MR ≠ P.
A monopolist’s demand curve P Q D
This slide introduces the notion that MR is not equal to P for the monopolist. The next slide presents an exercise to lead students to see for themselves what this relationship looks like.
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8. A C T I V E L E A R N I N G 1: A monopoly’s revenue
Moonbucks is the only seller of cappuccinos in town.
The table shows the market demand for cappuccinos.
Fill in the missing spaces of the table.
What is the relation between P and AR? Between P and MR? Q P TR AR MR
$4.50 1
4.00 2
3.50 3
3.00 4
2.50 5
2.00 6
1.50
n.a. 7

9. A C T I V E L E A R N I N G 1: AnswersQ P TR AR MR
Here, P = AR, same as for a competitive firm.
Here, MR < P, whereas MR = P for a competitive firm.
$4.50 9 10 7 4
$ 0
n.a. –1 1 2 3 $4 1
4.00
1.50
2.00
2.50
3.00
3.50
$4.00 2
3.50 3
3.00
When the AR column appears, note that AR = P at every quantity. This, of course, is a tautology.
When the MR column appears, note that MR is less than P. This is not as easy to see, because the MR numbers are offset from the rows of the table, just as if you were in an elevator stuck between two floors. But students can still see that MR < P.
For example, in the range of output of Q=2 to Q=3, the price ranges from $3.50 to $3.00, but MR is only $2. 4
2.50 5
2.00 6
1.50 8

10. Moonbuck’s D and MR Curves
P, MR $ 5
Demand curve (P) 4 MR 3 2 1
These curves are based on the preceding exercise. This graph shows visually what the table showed with columns of numbers: MR < P. -1 -2 -3 Q 1 2 3 4 5 6 7
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11. Understanding the Monopolist’s MR
Increasing Q has two effects on revenue:
The output effect: More output is sold, which raises revenue
The price effect: The price falls, which lowers revenue
To sell a larger Q, the monopolist must reduce the price on all the units it sells.
Hence, MR < P
MR could even be negative if the price effect exceeds the output effect (e.g., when Moonbucks increases Q from 5 to 6).
Note that a competitive firm has the output effect but not the price effect: the competitive firm does not need to reduce its price in order to sell a larger quantity, so, for the competitive firm, MR = P.
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12. Profit-Maximization
Like a competitive firm, a monopolist maximizes profit by producing the quantity where MR = MC.
Once the monopolist identifies this quantity, it sets the highest price consumers are willing to pay for that quantity.
It finds this price from the D curve.
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13. Profit-Maximization 1. The profit- maximizing Q is where MR = MC.
Quantity
Costs and Revenue
1. The profit- maximizing Q is where MR = MC.
2. Find P from the demand curve at this Q. D MR MC P Q
Profit-maximizing output
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14. The Monopolist’s Profit
Quantity
Costs and Revenue
ATC D MR MC
As with a competitive firm, the monopolist’s profit equals
(P – ATC) x Q P
ATC Q
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15. A Monopoly Does Not Have an S Curve
A competitive firm
takes P as given
has a supply curve that shows how its Q depends on P
A monopoly firm
is a “price-maker,” not a “price-taker”
Q does not depend on P; rather, Q and P are jointly determined by MC, MR, and the demand curve.
So there is no supply curve for monopoly.
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16. Case Study: Monopoly vs. Generic Drugs
The market for a typical drug
Patents on new drugs give a temporary monopoly to the seller.
When the patent expires, the market becomes competitive, generics appear.
Quantity
Price D MR PM QM
PC = MC QC
Here, we assume constant marginal cost, for simplicity.
PM and QM denote the monopoly price and quantity, respectively.
PC and QC denote the competitive price and quantity, respectively.
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17. The Welfare Cost of Monopoly
Recall: In a competitive market equilibrium, P = MC and total surplus is maximized.
In the monopoly eq’m, P > MR = MC
The value to buyers of an additional unit (P) exceeds the cost of the resources needed to produce that unit (MC).
The monopoly Q is too low – could increase total surplus with a larger Q.
Thus, monopoly results in a deadweight loss.
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18. The Welfare Cost of Monopoly
Competitive eq’m:
quantity = QE
P = MC
total surplus is maximized
Monopoly eq’m:
quantity = QM
P > MC
deadweight loss
Quantity
Price
Deadweight loss D MR MC P MC QM
P = MC QE
It’s worth mentioning the following:
Most people know that monopoly changes the way the economic “pie” is divided: by charging higher prices, the monopoly gets more surplus and consumers get less surplus.
The analysis on this slide shows that the monopoly also reduces the size of the economic pie – by producing less than the socially efficient quantity and causing a deadweight loss.
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19. Public Policy Toward Monopolies
Increasing competition with antitrust laws
Examples: Sherman Antitrust Act (1890), Clayton Act (1914)
Antitrust laws ban certain anticompetitive practices, allow govt to break up monopolies.
Regulation
Govt agencies set the monopolist’s price
For natural monopolies, MC < ATC at all Q, so marginal cost pricing would result in losses.
If so, regulators might subsidize the monopolist or set P = ATC for zero economic profit.
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20. Public Policy Toward Monopolies
Public ownership
Example: U.S. Postal Service
Problem: Public ownership is usually less efficient since no profit motive to minimize costs
Doing nothing
The foregoing policies all have drawbacks, so the best policy may be no policy.
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21. Price Discrimination
Discrimination is the practice of treating people differently based on some characteristic, such as race or gender.
Price discrimination is the business practice of selling the same good at different prices to different buyers.
The characteristic used in price discrimination is willingness to pay (WTP):
A firm can increase profit by charging a higher price to buyers with higher WTP.
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22. Perfect Price Discrimination vs. Single Price Monopoly
Here, the monopolist charges the same price (PM) to all buyers.
A deadweight loss results.
Consumer surplus
Quantity
Price D MR
Deadweight loss PM QM
Monopoly profit MC
To keep the graph simple, this example assumes constant marginal cost.
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23. Perfect Price Discrimination vs. Single Price Monopoly
Here, the monopolist produces the competitive quantity, but charges each buyer his or her WTP.
This is called perfect price discrimination.
The monopolist captures all CS as profit.
But there’s no DWL.
Quantity
Price
Monopoly profit D MR MC Q
Here, there is no horizontal price line. The “price line”, if you will, is the demand curve:
at each Q, the height of the demand curve shows the marginal buyer’s willingness to pay, which is the price the monopolist charges that buyer under perfect price discrimination.
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24. Price Discrimination in the Real World
In the real world, perfect price discrimination is not possible:
no firm knows every buyer’s WTP
buyers do not announce it to sellers
So, firms divide customers into groups based on some observable trait that is likely related to WTP, such as age.
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25. Examples of Price Discrimination
Movie tickets Discounts for seniors, students, and people who can attend during weekday afternoons. They are all more likely to have lower WTP than people who pay full price on Friday night.
Airline prices Discounts for Saturday-night stayovers help distinguish business travelers, who usually have higher WTP, from more price-sensitive leisure travelers.
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26. Examples of Price Discrimination
Discount coupons People who have time to clip and organize coupons are more likely to have lower income and lower WTP than others.
Need-based financial aid Low income families have lower WTP for their children’s college education. Schools price-discriminate by offering need-based aid to low income families.
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27. Examples of Price Discrimination
Quantity discounts A buyer’s WTP often declines with additional units, so firms charge less per unit for large quantities than small ones.
Example: A movie theater charges $4 for a small popcorn and $5 for a large one that’s twice as big.
In this example, the firm is not charging different prices to different customers, but charging different prices to the same customer based on that customer’s declining willingness to pay for additional units.
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28. CONCLUSION: The Prevalence of Monopoly
In the real world, pure monopoly is rare.
Yet, many firms have market power, due to
selling a unique variety of a product
having a large market share and few significant competitors
In many such cases, most of the results from this chapter apply, including
markup of price over marginal cost
deadweight loss
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29. CHAPTER SUMMARY
A monopoly firm is the sole seller in its market. Monopolies arise due to barriers to entry, including: government-granted monopolies, the control of a key resource, or economies of scale over the entire range of output.
A monopoly firm faces a downward-sloping demand curve for its product. As a result, it must reduce price to sell a larger quantity, which causes marginal revenue to fall below price.
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30. CHAPTER SUMMARY
Monopoly firms maximize profits by producing the quantity where marginal revenue equals marginal cost. But since marginal revenue is less than price, the monopoly price will be greater than marginal cost, leading to a deadweight loss.
Policymakers may respond by regulating monopolies, using antitrust laws to promote competition, or by taking over the monopoly and running it. Due to problems with each of these options, the best option may be to take no action.
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31. CHAPTER SUMMARY
Monopoly firms (and others with market power) try to raise their profits by charging higher prices to consumers with higher willingness to pay. This practice is called price discrimination.
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