Monopoly and Monopsony (Market structures and Contestability)

A monopoly is a market structure with a single seller (a pure monopoly), or in practice a dominant firm with a very high market share. In the UK a firm is legally investigated for monopoly behaviour once it holds 25% or more of a market, but in exam theory we usually treat monopoly as one firm = the whole industry.

The feature that makes monopoly powerful is high barriers to entry — obstacles that stop new firms competing the incumbent away. These include:

• Patents and legal protection (a legal monopoly over an invention),
• High start-up or sunk costs (huge capital needed to enter, e.g. a rail network),
• Control of a key resource (owning the only supply of an input),
• Economies of scale (an established large firm has much lower AC than any small entrant — see natural monopoly),
• Brand loyalty and advertising that new entrants cannot match.

The key consequence: the monopolist is a price-maker. With no close rivals and entry blocked, the firm is not a price-taker. It faces the whole market's downward-sloping demand (AR) curve and can choose its price OR its output (but not both independently — pick one and the demand curve fixes the other). This is the exact opposite of perfect competition, where each tiny firm faced a horizontal demand curve at a price it had to accept. Everything in the monopoly diagram flows from this single fact: AR slopes downward, so MR lies below AR.

This is the most examined diagram in the subtopic. Because AR slopes downward, the monopolist must cut its price to sell more, so the extra revenue from one more unit (MR) is less than the price on that unit — the 'lost-revenue effect'. That is why MR lies below AR and is twice as steep.

Build it in the order examiners check:

1. Draw the four curves. A downward AR = D (demand) curve, and below it, twice as steep, the MR curve. A U-shaped MC and a U-shaped AC, with MC cutting AC at AC's minimum.
2. Fix the output first. Find Qm where MC = MR and drop a vertical line to the axis. This is the profit-maximising output.
3. Read the price off AR — never off MR. Go straight up from Qm to the AR curve to find Pm. This is the crucial monopoly step: the price sits on AR, above the MR value.
4. Read average cost off AC. At Qm, the height of the AC curve gives cost per unit ACm.
5. Shade the profit. Because $Pm > ACm$, the firm makes supernormal profit = the rectangle between AR (top, at Pm) and AC (bottom, at ACm), from the axis across to Qm: area $(Pm - ACm) \times Qm$.

The long-run twist. In perfect competition this profit would be competed away. Under monopoly, high barriers to entry block new firms, so the supernormal profit persists in the long run — the single most important difference between the two structures.

Set the monopoly outcome against a competitive market for the same industry, and the classic costs to society appear:

• Higher price and lower output. Restricting output to Qm (where MC = MR) and charging Pm off the demand curve gives a higher price and lower quantity than a competitive market, which would produce more at a lower price. Consumers lose out and there is a welfare (deadweight) loss.
• Allocative inefficiency ($P > MC$). At Qm the price on the AR curve (Pm) is above the marginal cost (the MC height at Qm). Because $P > MC$, the value consumers place on the last unit exceeds its cost of production, so too little is produced — resources are misallocated. (Contrast perfect competition, where $P = MC$.)
• Productive inefficiency. The monopolist produces at Qm, which is not at the minimum of AC, so it does not produce at lowest average cost — resources are wasted per unit compared with the productively efficient output.
• X-inefficiency. With no competitive pressure, a monopolist may let costs drift upward — organisational slack, overstaffing, weak cost control — so its whole AC curve sits higher than it need be. This 'quiet life' waste is unique to markets without competition.

Beyond the diagram, monopoly power can also mean less choice for consumers and, if the firm becomes complacent, lower quality or slower service. These are the AO3 costs you develop and the AO4 case against monopoly.

A top-band answer never treats monopoly as simply 'bad'. There are real potential benefits, and these drive the evaluation:

Economies of scale and the natural monopoly. A large monopolist can spread fixed costs over huge output, achieving economies of scale that many small firms cannot. In a natural monopoly — such as water pipes, the rail network or the electricity grid — the fixed infrastructure cost is so high that a single firm supplies at a lower average cost than several competing firms duplicating the network. Here monopoly can actually mean lower prices than fragmented competition.

Dynamic efficiency and innovation. Because barriers to entry let a monopolist keep supernormal profit in the long run, it has funds to invest in research and development (R&D) and the incentive to innovate (patents protect the reward). This dynamic efficiency — better products and lower costs over time — is exactly what perfect competition lacked. Schumpeter argued that this innovation ('creative destruction') is the main engine of long-run growth.

Cross-subsidy. A monopolist earning profit on some routes or products can use it to subsidise loss-making but socially valuable ones (e.g. a postal service delivering to remote areas at the same price).

Price discrimination. A monopolist with price-setting power can charge different prices to different groups for the same good — for example cheaper off-peak train tickets, student or pensioner discounts. This can raise the firm's profit and widen access, letting some consumers buy who could not afford a single uniform price. The conditions for it are covered next.

The evaluation, therefore, is a judgement: monopoly's higher prices and inefficiency must be weighed against the scale, innovation and (in a natural monopoly) lower costs it can deliver — and whether regulation could capture the benefits while curbing the harms.

Price discrimination is charging different prices to different consumers (or groups) for the same product, where the price difference is not justified by a difference in cost. Classic examples: off-peak versus peak rail fares, student and pensioner discounts, and airline seats priced by how far ahead you book.

For price discrimination to work, four conditions must hold:

1. Price-setting power. The firm must be a price-maker (a monopoly or firm with market power) — a price-taker cannot do it.
2. Separable markets / identifiable groups. The firm must be able to split consumers into groups it can charge differently (by time, age, location, or booking behaviour).
3. Different price elasticities of demand (PED). The groups must have different PEDs. The firm charges a higher price to the group with inelastic demand (who will still buy) and a lower price to the group with elastic demand (who are price-sensitive).
4. Ability to prevent resale (no seepage). Consumers in the cheap market must not be able to resell to those in the expensive market, or the scheme collapses.

Effects. Price discrimination usually raises the firm's supernormal profit (it captures more consumer surplus). For consumers the effect is mixed: those paying the higher price lose, but those in the elastic, low-price group may gain access they would not have had at a single uniform price — and the extra profit can fund investment or cross-subsidy. This mixed verdict is the evaluation.

A monopsony is market power on the buying side — a single (or dominant) buyer. The classic case is a monopsony employer of labour (e.g. the only large employer in a town, or a national health service as the main employer of nurses), but it also applies to a dominant buyer of suppliers' output (e.g. a supermarket chain buying from many small farmers).

The key mechanic is the cost of hiring more. A monopsonist faces the upward-sloping supply curve of labour as its average cost of labour (ACL) — to attract more workers it must raise the wage. But because it must pay the higher wage to all workers, not just the new one, the marginal cost of labour (MCL) — the extra cost of one more worker — lies above the supply/ACL curve and rises faster (roughly twice as steep). Hiring one more worker at £11 when everyone was on £10 costs the extra £11 plus the £1 rise on every existing worker.

Read the diagram in a fixed order:

1. The curves. Upward S = ACL (supply of labour = average cost of labour); above it, steeper, MCL (marginal cost of labour); downward MRP = D (marginal revenue product — the demand for labour, the value each worker adds).
2. Hire where MCL = MRP. The monopsonist maximises profit by hiring up to Qm, where the cost of the last worker (MCL) equals the revenue that worker generates (MRP). Note this is fewer workers than a competitive market would hire.
3. Pay the wage off supply, not off MCL. At Qm, workers are willing to supply for the wage on the S = ACL curve, so the monopsonist pays only Wm — read down from Qm to the supply curve. It does not pay the MCL height.
4. Compare with competition. A competitive labour market hires where S = MRP (point Qc), paying the higher wage Wc. So the monopsonist hires fewer workers (Qm < Qc) at a lower wage (Wm < Wc).

Effects. Workers (or suppliers) are worse off — lower wages/prices and fewer jobs. Suppliers to a dominant buyer face squeezed prices. But the story is not all bad: the monopsonist's lower input costs can be passed on as lower prices to consumers, and a monopsony employer can act as a countervailing power against a strong trade union. As always, the net effect is a judgement.