How Markets Work

A market is any place where buyers and sellers meet to trade. This sub-theme is the engine room of the course: demand, supply, elasticity and the price mechanism that brings them together.

Learning objectives — by the end of 1.2 you can…

- draw demand and supply curves and distinguish movements from shifts; - calculate and interpret PED, YED, XED and PES, and link PED to total revenue; - find market equilibrium and explain how the price mechanism allocates resources; - analyse consumer & producer surplus and the effects of indirect taxes and subsidies; - explain why real consumers don't always behave rationally.

1.2.1 Rational decision making

Traditional economic theory assumes everyone is rational — they weigh up costs and benefits and choose the option that makes them best off:

Consumers aim to maximise their utility (satisfaction/welfare).
Firms aim to maximise profit.
Workers aim to maximise their own welfare (wages, conditions).
Governments aim to maximise social welfare.

This assumption is what makes neat demand and supply curves possible. Keep it in mind — section 1.2.10 shows how often it breaks down in the real world.

1.2.2 Demand

Demand is the quantity of a good consumers are willing and able to buy at each price over a period of time. The law of demand states that as price rises, quantity demanded falls, ceteris paribus — giving a downward-sloping demand curve.

Three reasons explain the downward slope:

Income effect — a price fall makes consumers relatively richer, so they buy more.
Substitution effect — a price fall makes this good cheaper than rivals, so buyers switch to it.
Diminishing marginal utility — each extra unit gives less additional satisfaction, so people will only buy more at a lower price.

Conditions of demand — what shifts the curve

Anything except the good's own price. Useful checklist:

- Real income — more income, more demand (for normal goods) - Tastes & fashion / advertising - Prices of substitutes & complements (related goods) - Population & demographics - Expectations of future prices - Interest rates (for goods bought on credit, e.g. cars, houses)

Watch Out

A price change never shifts the demand curve — it moves you along it. Mixing these up is the single most common diagram error at AS/A-level.

Worked Example — diminishing marginal utility

Imagine eating slices of pizza when hungry. The marginal utility (extra satisfaction) from each slice falls:

| Slice | 1st | 2nd | 3rd | 4th | 5th | | --- | --- | --- | --- | --- | --- | | Extra satisfaction | 10 | 7 | 4 | 1 | −2 |

Because each slice is worth less to you, you'd only buy more at a lower price — which is exactly why the demand curve slopes downward.

Exceptions to the law of demand

A few goods can have an upward-sloping demand curve, where higher prices attract more demand:

- Veblen (ostentatious) goods — luxury items like designer handbags bought because they're expensive, as a status symbol. - Giffen goods — very rare; basic staples for the poor where a price rise forces people to buy more of it and less of pricier alternatives. - Speculative demand — assets (housing, shares, crypto) where a rising price makes buyers expect further rises, so demand grows.

1.2.3 Elasticities of demand — PED, YED & XED

Elasticity measures how responsive demand is to a change in a variable. Three to master:

#### ① Price elasticity of demand (PED)

PED = % change in quantity demanded ÷ % change in price

Always negative (price & quantity move in opposite directions) — we look at the size, ignoring the minus sign.

Determinants of PED

- Substitutes available — more substitutes → more elastic - Proportion of income spent — expensive items → more elastic - Necessity or luxury — necessities → inelastic - Addictiveness / habit — addictive goods → inelastic - Time period — demand is more elastic in the long run - Brand loyalty & how the market is defined

Worked Example — PED & total revenue

A train operator raises fares by 10% and finds passenger numbers fall by 4%.

PED = −4% ÷ +10% = −0.4 → demand is inelastic (\|0.4\| < 1).

Effect on revenue: because quantity fell by less than price rose, total revenue rises. This is the key link: raise price on an inelastic good and revenue increases; raise price on an elastic good and revenue falls.

#### ② Income elasticity of demand (YED)

YED = % change in quantity demanded ÷ % change in income

#### ③ Cross elasticity of demand (XED)

XED = % change in quantity demanded of Good A ÷ % change in price of Good B

Substitutes → XED is positive (price of Pepsi up → demand for Coke up). e.g. +1.2.
Complements → XED is negative (price of printers up → demand for ink down). e.g. −0.8.
Unrelated goods → XED ≈ 0.

The further from zero, the stronger the relationship.

Exam Tip — why firms & governments care

Elasticity isn't abstract. Firms use PED to set prices (price discrimination), YED to plan for booms and recessions (luxury firms suffer most in downturns), and XED to track rivals. Governments use PED to predict the revenue from taxing inelastic goods like tobacco and fuel.

Worked Examples — YED & XED

YED: Incomes rise 5% and demand for restaurant meals rises 8%. YED = +8% ÷ +5% = +1.6 → a normal luxury (income elastic). In a recession, demand for these goods falls fastest.

YED (inferior): Incomes rise 5% and demand for own-brand baked beans falls 2%. YED = −2% ÷ +5% = −0.4 → an inferior good.

XED: The price of Coca-Cola rises 10% and demand for Pepsi rises 6%. XED = +6% ÷ +10% = +0.6 → a positive value confirms they are substitutes, and the size (0.6) shows a fairly close one.

The link between PED and a firm's total revenue (price × quantity) is one of the most-tested ideas in Theme 1. Along a straight-line demand curve, PED is not constant — it falls as you move down:

1.2.4 Supply

Supply is the quantity producers are willing and able to sell at each price over a period of time. The law of supply: as price rises, quantity supplied rises — an upward-sloping curve. Higher prices mean more profit, cover rising marginal costs, and attract new firms into the market.

Conditions of supply — what shifts the curve

- Costs of production — wages, raw materials, energy (lower costs → supply right) - Technology & productivity improvements → supply right - Number of firms in the market - Indirect taxes (shift left) and subsidies (shift right) - Weather / external shocks (especially agriculture) - Expectations of future prices

1.2.5 Elasticity of supply (PES)

PES = % change in quantity supplied ÷ % change in price

Normally positive, since supply and price move together.

PES tells you how easily producers can expand output when price rises. The same elastic / inelastic bands apply as for PED.

Determinants of PES

- Spare capacity — idle machines/workers → easy to expand → elastic - Stocks (inventories) available → elastic - Mobility of factors — how easily resources switch to this product - Time period — supply is far more elastic in the long run - Spare raw materials & barriers to entry

Worked Example — PES

A clothing factory with spare capacity raises output by 15% when price rises 6%. PES = +15% ÷ +6% = +2.5 → supply is elastic: the firm can respond quickly. Compare farmland, where a 6% price rise might raise supply only 1% in a season (PES = +0.17, inelastic) because the harvest is fixed.

Related supply concepts

Joint supply — Producing one good automatically produces another (beef & leather). More demand for beef raises the supply of leather.

Competitive supply — Resources can make one good or another (a farmer's field: wheat or barley). Producing more of one means less of the other.

Real World

Agricultural and primary commodities (coffee, oil, copper) have inelastic supply in the short run — you can't grow a coffee crop overnight. Combined with inelastic demand, this is why commodity prices are so volatile: a small supply shock causes a big price swing.

1.2.6 Price determination

Bring demand and supply together and the market settles at equilibrium — the price where the quantity demanded exactly equals the quantity supplied. The market "clears": no shortage, no surplus.

Away from equilibrium the market is in disequilibrium, and price automatically corrects it:

Exam Tip — shift questions

To predict a new equilibrium, shift the right curve and read off the change. Memorise the four outcomes: ↑Demand → P↑ Q↑; ↓Demand → P↓ Q↓; ↑Supply → P↓ Q↑; ↓Supply → P↑ Q↓. Always draw it.

1.2.7 The price mechanism

In a free market, prices do the job that a central planner would otherwise have to do — Adam Smith's famous "invisible hand." The price mechanism performs three functions (remember RIS):

Through these signals, resources are allocated automatically — and the mechanism works at every level, from a local farmers' market to national housing markets and global oil markets.

1.2.8 Consumer & producer surplus

Markets create welfare for both sides of a trade, and we can see it on the diagram:

Key Terms

Consumer surplus — The difference between the price a consumer is willing to pay and the price they actually pay. (Area below the demand curve, above the price.)

Producer surplus — The difference between the price a producer receives and the minimum they were willing to accept. (Area above the supply curve, below the price.)

1.2.9 Indirect taxes & subsidies

An indirect tax is a tax on spending (it's collected by the seller and passed to the government). There are two kinds:

Specific tax — a fixed amount per unit (e.g. £0.54 per litre of fuel duty). Shifts supply up by the same amount everywhere → a parallel shift.
Ad valorem tax — a percentage of the price (e.g. 20% VAT). The gap widens as price rises → a diverging (pivoted) shift.

Either way the supply curve shifts left/up by the tax: price rises, quantity falls.

The diagram above shows a specific tax (a parallel shift). An ad valorem tax (a percentage, like VAT) pivots the supply curve instead — the gap between the two curves widens as the price rises:

Worked Example — who pays the tax?

A £2 specific tax is placed on a good. Before the tax: price £10, quantity 100. After the tax: consumers pay £11, quantity falls to 90.

- Consumer's share = £11 − £10 = £1 per unit. - Producer's share = £2 − £1 = £1 per unit (they net £9, £1 less than before). - Government revenue = £2 × 90 = £180.

Here the burden split 50:50, so PED and PES were equal. Make demand more inelastic and the consumer's share would grow — buyers can't easily cut back.

A subsidy is the mirror image: a government payment to producers that lowers their costs, shifting supply right/down. Price falls, quantity rises.

Evaluation — do taxes & subsidies work?

It depends on elasticity. Taxing a good with inelastic demand (cigarettes, fuel) raises lots of revenue but barely cuts consumption — good for the Treasury, weak for changing behaviour. Subsidies can be expensive, may be captured as producer profit rather than lower prices, and create an ongoing burden on taxpayers. Always question: who really bears the cost, and is it the best use of public money?

1.2.10 Alternative views of consumer behaviour

Everything so far assumed consumers are perfectly rational. Behavioural economics shows they often aren't — real people use shortcuts and make systematic mistakes. The spec highlights four reasons:

Real World — nudges

Governments use these insights to design "nudges" and choice architecture. The classic success is pension auto-enrolment: making saving the default (you opt out rather than in) hugely increased the number of people saving — without banning anything or changing prices.

1.2 Recap — nail these

- Equilibrium is where S = D; disequilibrium self-corrects via excess demand/supply. - The price mechanism rations, incentivises and signals (RIS) — Smith's invisible hand. - Consumer + producer surplus measure the welfare a market generates. - An indirect tax shifts S up; a subsidy shifts S down. Who bears the burden depends on elasticity. - PED/YED/XED: master the formulas, the value bands, and the link to total revenue. - Real consumers are boundedly rational — opening the door to nudges.