Monopoly vs Market Power
Monopoly and Market Power are related concepts in AP Economics that students often mix up. A monopoly is a market structure with a single seller producing a unique product with no close substitutes and significant barriers to entry. Market power is a firm's ability to raise price above marginal cost without losing all of its buyers, which comes from facing a downward-sloping demand curve. Here is how they compare side by side.
A monopolist is the sole provider of a good or service and faces the entire market demand curve, allowing it to set price above marginal cost. Because of high barriers to entry, other firms cannot enter the market to compete.
A firm with no market power is a price taker: its demand curve is flat at the market price, and raising price by a cent loses every customer. A firm with market power faces a downward-sloping demand curve, so it can charge more and keep most of its buyers, though it must accept selling fewer units. The power comes from barriers to entry, a differentiated product, control of a scarce input, patents, network effects, or simply having few rivals. The cost to society is that price sits above marginal cost, so output stops short of the efficient quantity and deadweight loss appears. Market power is a matter of degree rather than a category: monopoly is the extreme case, but a corner shop, a branded cereal and a neighborhood restaurant each hold a little of it.
Monopoly vs Market Power: One Is a Structure, the Other Is a Degree
| Monopoly | Market Power | |
|---|---|---|
| What the word describes | A market structure with a single seller | A firm's ability to price above marginal cost |
| Kind of answer it gives | Yes or no, based on how many sellers there are | How much, on a sliding scale |
| Demand curve involved | The whole market demand curve belongs to the one firm | Any curve that slopes down, however slightly |
| Which firms have it | Very few markets qualify | Every firm outside perfect competition, including a corner cafe |
| How it is measured | Share of the market, at or close to all of it | The gap between price and marginal cost, divided by price |
| What takes it away | The arrival of a second seller | Substitutes close enough that buyers leave when the price rises |
| Legal position in the United States | Holding the position is not itself unlawful | Never unlawful by itself; only conduct used to get or keep it can be |
Monopoly is a yes or no answer, market power is a reading on a dial
Market power comes with a number attached. The standard measure takes the gap between price and marginal cost and divides it by the price. A cafe that sells a sandwich for 20 dollars when one more sandwich costs 16 dollars to make has a gap of 4 dollars, so it scores 4 divided by 20, which is 0.20. A firm in perfect competition scores zero, because price equals marginal cost. A single seller charging 90 dollars where the extra unit costs 30 dollars scores 60 divided by 90, which is two thirds, or about 0.67. For a firm charging its profit maximizing price, that score also equals one divided by the elasticity of demand it faces. So 0.20 implies an elasticity of 5 and two thirds implies an elasticity of 1.5. Read the two cases side by side and the difference is a matter of degree, not of kind. Raise the cafe's price and buyers walk to the shop next door quickly. Raise the single seller's price and buyers mostly stay, because there is nowhere close to go. The cafe is nobody's idea of a monopoly, yet it does have some power over its own price, which is exactly what the scale is built to capture.
Nearly every firm has some market power, and almost none of them is a monopoly
All it takes to have market power is a demand curve that slopes down, meaning the firm can raise its price a little and keep most of its customers. Location does it. A brand does it. So does anything that makes one seller's version not quite the same as another's, which is why every firm in /glossary/monopolistic-competition has power over its own price and yet none of them controls the market. Monopoly is a much stronger claim: one seller, no close substitutes, and entry blocked. The two can even come apart in the other direction. A firm that is the only seller today can have very little power if a rival could set up next week at low cost, since any attempt to raise the price would invite one in. That is the point of /glossary/contestable-market, and it is why counting sellers is a poor shortcut for measuring power. There is also a definitional trap on exams. Whether a firm looks dominant depends on how narrowly the market is drawn, since the only seller of one brand may be one of many sellers of a product category. Draw the market wrong and the power estimate is wrong with it.
Frequently asked questions
Does market power mean the same thing as monopoly?
No, market power is the ability to set a price above marginal cost without losing all buyers, and any firm facing a downward sloping demand curve has some of it, while a monopoly is the specific structure in which one seller supplies the whole market. Every monopoly has market power, but most firms with market power are not monopolies. Market power is a matter of degree, and monopoly is a description of the structure.
Can a small firm have market power?
Yes, a small firm has market power whenever it can raise its price slightly and keep most of its customers, which is true of almost any seller with a distinctive location, brand or product. A neighborhood restaurant that raises prices a little does not lose every diner. The amount of power is small, but it is not zero, and only a price taker in perfect competition has none at all.
How is market power measured?
The most common measure divides the gap between price and marginal cost by the price, which gives zero under perfect competition and rises toward one as the firm's pricing freedom grows. Market share and concentration measures are used as rough stand ins because costs are hard to observe from outside. Neither number is decisive on its own, since easy entry can hold prices down even when one firm holds the whole market today.
Live Monopoly graph. Drag the curves, or open the full version.
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