Monopoly: barriers to entry, the profit-maximising equilibrium with abnormal profit, the efficiency loss compared with perfect competition, and the conditions for and types of price discrimination.

What this key area is asking

Monopoly is the opposite pole to perfect competition, and the course uses the contrast to drive its efficiency arguments. You must explain the barriers to entry that create and protect a monopoly, derive its profit-maximising equilibrium (with $MR$ below $AR$ on a downward-sloping demand curve), show how it restricts output and raises price relative to perfect competition, and assess the resulting efficiency loss with possible offsets. You then study price discrimination: when a firm with market power can charge different buyers different prices, and why it does.

Barriers to entry: what creates a monopoly

A monopoly survives because rivals cannot enter. The main barriers to entry are:

• Legal barriers: patents, copyright, licences and state-granted monopolies.
• Control of an essential resource: ownership of a key input or distribution network.
• Economies of scale: when minimum efficient scale is large relative to the market, one big firm has far lower costs than any small entrant (a "natural monopoly").
• High sunk costs and brand loyalty: heavy advertising and irrecoverable set-up costs deter entry.

Without barriers, abnormal profit would attract entry and competition away, as in perfect competition; the barriers are precisely what let a monopoly keep abnormal profit in the long run.

Monopoly equilibrium

The monopolist is the industry, so it faces the downward-sloping market demand curve as its average revenue curve. To sell more it must lower the price on all units, so:

It maximises profit, like any firm, where $MC = MR$. This gives output $Q_m$; the price $P_m$ is then read up to the demand curve, so $P_m > MR$. Because barriers block entry, $P_m > AC$ can persist, giving long-run abnormal profit.

Monopoly versus perfect competition

The standard comparison drives the welfare verdict. A competitive industry produces where price equals marginal cost ($P = MC$); a monopoly produces where $MC = MR$, and since $P > MR$, it follows that $P > MC$ at its output.

So the monopoly restricts output and raises price, and is allocatively inefficient: some units that consumers value above their marginal cost go unproduced. The lost welfare is the deadweight loss triangle between the demand and $MC$ curves over the missing output.

Are monopolies always bad? The offsets

A top answer evaluates rather than condemns. Possible benefits of monopoly:

• Economies of scale: a single large producer may achieve much lower average costs, so price could be lower than under many small firms.
• Dynamic efficiency: abnormal profit can fund research, development and innovation that competitive firms (on normal profit only) cannot afford.
• Natural monopoly: in industries such as water or rail track, duplicating the network would be wasteful, so a single regulated supplier is efficient.

The verdict therefore depends on whether scale economies and innovation outweigh the static allocative loss, which is why monopoly is usually a case for regulation rather than outright prohibition.

Price discrimination

A firm with market power can sometimes charge different prices to different buyers for the same good.

It then charges a higher price in the inelastic market and a lower price in the elastic market. Economists distinguish three degrees:

• First degree (perfect): each buyer is charged the maximum they will pay; all consumer surplus is captured.
• Second degree: price varies with the quantity bought (bulk discounts, tariff blocks).
• Third degree: different groups pay different prices (student versus adult, peak versus off-peak).

The motive is to convert consumer surplus into profit, and sometimes to serve customers who could not be served profitably at a single price.

Worked example: monopoly output and price

Why this matters

Monopoly is the structure that most clearly shows a market failing to deliver the competitive ideal: higher price, lower output, lasting abnormal profit and an allocative welfare loss. That is exactly the case for government intervention, regulation, competition law and price controls, which you study next. Price discrimination, meanwhile, shows how market power is used in practice and feeds into both pricing analysis and the fairness debates that often appear in the project.

Try this

Q1. Explain why a monopolist's marginal revenue lies below its average revenue. [2 marks]

• Cue. The monopolist faces a downward-sloping demand curve, so to sell an extra unit it must lower price on all units; the revenue lost on existing units pulls $MR$ below the price ($AR$).

Q2. State two conditions a firm needs to practise price discrimination. [2 marks]

• Cue. Any two of: price-setting power (not a price taker); buyers with different price elasticities of demand; the ability to separate markets and prevent resale.