IGCSE Economics — Basic Ideas and the Price Mechanism
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Lesson overview
Scarcity, opportunity cost, demand and supply, elasticity, and the market failure that justifies intervention.
Go to lesson quiz →Exam guidance · Cambridge IGCSE Command-Word Lens
Core idea (Supply, Demand, Market Equilibrium & Elasticity): Own-price changes move ALONG the curve; non-price determinants SHIFT the entire curve. When PED > 1 (elastic), cutting price raises total revenue.
Pacing
~1 minute per mark; match answer depth strictly to `[1]`, `[2]`, `[3]`, or `[4]` mark allocations.
How IGCSE marks this
Command words govern mark schemes: 'State' = 1 concise fact; 'Describe' = what happens; 'Explain' = why/how using scientific terminology.
Watch out for
Vague everyday wording ('it gets bigger') fails Cambridge mark schemes where exact terms ('rate of collisions increases') are required.
Lesson content
The problem economics starts from
Every answer in this part of the syllabus begins with the same three terms: NEEDS are unlimited, RESOURCES are scarce, so choices must be made, and the value of the next-best alternative given up is the OPPORTUNITY COST. Candidates lose marks by writing 'cost' where the question asks for opportunity cost, or by forgetting that for the state the cost of a hospital is the value of what the same resources would have produced elsewhere — which is exactly what a production-possibility curve shows: a move along the curve is a reallocation whose cost is the other good's lost output, a point inside is unemployment of resources, and a point outside is unattainable with today's resources and technology (attainable only through economic growth). Growth itself is an increase in the quantity or quality of resources or in technology, measured as real GDP per head, and the standard of living differs from quality of life because the latter includes literacy, life expectancy and leisure, which national income only partly reflects. The PRICE MECHANISM is then the allocation device: buyers express demand, sellers supply, and the price adjusts until quantity demanded equals quantity supplied. A rise in price moves along the demand curve (contraction of demand); a change in income, taste, the price of a substitute or complement, or expectations shifts the whole curve. Knowing which is asked is most of the mark. Elasticity measures responsiveness: price elasticity of demand is the percentage change in quantity over the percentage change in price, and a firm raising price gains revenue only when demand is inelastic (coefficient below 1); supply elasticity decides who bears a tax; income elasticity separates normal from inferior goods; cross elasticity separates substitutes from complements. The reasons elasticity is low — necessity, no substitutes, a short time period, small share of income — are examinable as a list and repay memorising in that order. Market failure is the reason government appears in every part of the syllabus: public goods are non-excludable and non-rival so the market will not supply them; a merit good (education, vaccination) is under-consumed when left to the market, a demerit good (cigarettes, gambling) over-consumed; a negative externality (pollution, congestion) puts costs on third parties, so the free market produces too much, and a positive externality (research, training) too little; information gaps and monopoly power distort allocation further. The remedies are examinable as instruments with their direction: indirect tax to close the gap between private and social cost, a subsidy for the externality's good side, legislation and tradable permits, and direct provision. Then the evaluation the structured paper pays for: a tax on inelastic demand raises revenue but changes behaviour little; a subsidy costs the Exchequer and may be captured by the producer; regulation is only as good as the enforcement that the state can afford.
The definitions that carry the marks
ECONOMIC PROBLEM: unlimited wants against scarce resources, forcing choice. OPPORTUNITY COST: the next-best alternative forgone, not the money paid. PRODUCTION-POSSIBILITY CURVE: the combinations of two goods an economy can produce with its resources. PRICE ELASTICITY OF DEMAND: percentage change in demand divided by percentage change in price. PUBLIC GOOD: non-excludable and non-rival, so not profitably supplied by the market. EXTERNALITY: a cost or benefit falling on someone outside the transaction.
Elasticity, revenue and the argument in four lines
A government raises the price of bottled drinks by 20% and quantity falls by 4%. PED = 4 ÷ 20 = 0.2, so demand is inelastic; total revenue from the tax rises, because price rises by more than quantity falls, and consumption falls by a small proportion — so the revenue objective succeeds while the health objective largely fails. Now the evaluation lines the paper wants: inelastic demand is typical of an addictive or necessary good with few substitutes, which is exactly the case for sugary drinks among regular consumers; the tax is regressive, taking a larger share of a poor household's income; and a fuller response combines the tax with information, labelling and the availability of substitutes, which shifts demand over time. Two sentences of arithmetic and two of judgment is a full-mark answer.
A merit good, argued both ways
'Vaccination is under-consumed in a free market.' Explain and evaluate. The explanation: individuals compare private benefit against private cost, ignoring the external benefit of herd protection, so the demand curve sits left of the socially optimal one and too little is consumed. The remedy has three grades, and the answer should rank them: free provision at the point of use (largest behavioural effect, and it removes information and cost barriers at once), subsidy (cheaper for the state but requires uptake), and compulsion or information campaigns (cheap, slow, and politically contested). The evaluation: the social benefit depends on the vaccine's efficacy and coverage thresholds, so the size of the subsidy is a judgment; free provision carries opportunity cost for the health budget; and if coverage is already high among the informed, the marginal gain from spending more is small. Mark schemes reward this shape: mechanism, one instrument with its effect, one drawback, one conditional sentence about when the policy works best.
Lesson summary
Scarcity, choice and opportunity cost are the frame; a production-possibility curve is the diagram that proves the cost of a decision. Distinguish a movement along a curve (own price) from a shift (any other determinant), and use elasticity to say what a price change does to revenue. Government steps in where the market fails — public goods, merit and demerit goods, externalities, information gaps — and every instrument must be named with its direction and its drawback.
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