Unit 2 Microeconomics HL

The law of demand states that, ceteris paribus, a higher price causes a lower quantity demanded and a lower price causes a higher quantity demanded over a stated period.

This Objective establishes the observable inverse relationship while holding income, tastes, related-good prices, expectations and consumer numbers constant. The deeper income, substitution and marginal-utility explanations belong to HL 2.1.2.

Identify the good's own price change, explicitly hold non-price determinants constant, and predict the opposite change in quantity demanded.

If coffee rises from $3 to$4 per cup while other conditions are unchanged, quantity demanded falls—for example from 120 to 90 cups per day.

Demand is the whole relationship; quantity demanded is one amount at one price. The law is ceteris paribus, not a claim that every observed sales change comes only from price.

At HL, three mechanisms support the law of demand. A price rise reduces real purchasing power (income effect), makes substitutes relatively cheaper (substitution effect), and confronts consumers with declining extra satisfaction from successive units (diminishing marginal utility).

For a normal good, a lower price increases real income and tends to increase quantity demanded. It also encourages substitution toward this now relatively cheaper good. Because marginal utility falls as consumption rises, extra units are normally chosen only at lower prices.

For a price change, explain the income and substitution channels separately, then connect marginal utility to consumers' willingness to pay for additional units.

When train fares fall, commuters may switch from buses because trains are relatively cheaper, and the same budget buys more travel. Additional trips provide less marginal benefit, so the consumer accepts them at the lower fare.

Ceteris paribus is assumed, but it is not itself the HL mechanism. Do not confuse the income effect of a price change with a separate shift caused by an actual change in income.

A demand curve plots price on the vertical axis and quantity demanded per stated period on the horizontal axis. It normally slopes downward from left to right, representing the law of demand.

Every point pairs one price with the quantity consumers are willing and able to buy, ceteris paribus. A demand schedule can be transferred point by point to the curve.

Label both axes and units, plot each price–quantity pair accurately, and describe the inverse relationship without treating the line as a time trend.

If quantity demanded is 100 units at $5 and 130 at$4, plot $(100,5)$ and $(130,4)$; the second point lies lower and farther right.

The curve is a model for a defined good, market and period. Movements and shifts are assessed separately in Objective 2.1.6.

Individual demand is one buyer’s schedule; market demand is the horizontal sum of quantities demanded by all buyers at each price.

Market demand changes when buyers enter or leave and reflects differences in incomes, tastes and substitution options.

Add quantities at the same price, not prices across buyers.

At $10, three consumers demand 2, 1 and 4 units, so market demand is 7 units.

Market demand is not the average of individual demand curves.

Income, tastes, prices of substitutes and complements, expectations, population and advertising can change demand at every price.

A substitute becoming more expensive can raise demand for this good; a complement becoming more expensive can reduce it. The effect depends on whether the good is normal or inferior.

Name the determinant, its direction and the resulting demand shift before predicting quantity.

If bus fares rise, demand for train travel may increase if buses are substitutes; if petrol rises, demand for large cars may fall.

Do not call a price change of the good itself a non-price determinant.

A movement along demand is caused by the good’s own price changing; a shift is caused by a non-price determinant changing.

A movement changes quantity demanded on one curve, while a shift changes demand at every price. Confusing them reverses the diagram and explanation.

Ask “did this good’s price change?” If yes, move along; if not, test income, tastes, related goods or expectations.

A fall in cinema ticket price moves down the curve; a successful film campaign shifts demand right.

A change in demand is not interchangeable with a change in quantity demanded.

The law of supply states that, ceteris paribus, a higher price causes a greater quantity supplied and a lower price causes a smaller quantity supplied over a stated period.

The own-price change alters the producer's incentive to offer units for sale while factor costs, technology, taxes, expectations and firm numbers remain constant. Rising marginal cost is the deeper HL explanation in Objective 2.2.2.

Identify the good's own price change, hold non-price determinants fixed, and predict a change in quantity supplied in the same direction.

If tomatoes rise from $2 to$3 per kilogram while production conditions are unchanged, growers may increase quantity supplied from 500 to 650 kilograms per day.

Supply means willingness and ability to sell, not all physical stock. The law is ceteris paribus and does not explain an observed change when production conditions also change.

At HL, the law of diminishing marginal returns states that, with at least one fixed factor, adding successive units of a variable factor eventually produces smaller additions to output.

When each extra worker or input adds less output, producing one additional unit requires more variable input. Marginal cost therefore rises, so firms normally require a higher price to make supplying additional units worthwhile—supporting an upward-sloping supply curve.

Identify the fixed and variable factors, show where marginal product begins to fall, connect this to rising marginal cost, then connect higher price to greater quantity supplied.

In a fixed-size kitchen, early additional cooks raise output strongly, but overcrowding eventually means each extra cook adds fewer meals. Extra meals then cost more labour to produce.

Diminishing marginal returns is a short-run production mechanism, not merely ceteris paribus and not the same as total output falling. Total output can still rise while marginal product falls.

A supply curve plots price on the vertical axis and quantity supplied per stated period on the horizontal axis. It normally slopes upward from left to right, representing the law of supply.

Every point pairs one price with the quantity producers are willing and able to sell, ceteris paribus. A supply schedule can be transferred point by point to the curve.

Label both axes and units, plot price–quantity pairs accurately, and describe the direct relationship without treating the line as a time trend.

If firms supply 100 units at $8 and 140 at$10, plot $(100,8)$ and $(140,10)$; the second point lies higher and farther right.

The curve represents a defined good, market and period and does not require identical costs across firms. Movements and shifts are assessed separately in Objective 2.2.6.

Individual supply is one producer’s schedule; market supply is the horizontal sum of quantities supplied by all producers at each price.

Entry, exit and different costs change market supply; add quantities at the same price.

Sum producer quantities at one price before plotting the market point.

At $5 three firms supply 2, 3 and 4 units, so market supply is 9 units.

Market supply is not the average of firm schedules.

Input prices, technology, taxes, subsidies, expectations, number of firms and natural conditions can change supply at every price.

Lower input costs or better technology usually shift supply right; a tax or disruption shifts it left, depending on incidence and capacity.

Name the determinant, direction and cost/incentive mechanism before predicting the shift.

A subsidy lowers effective production cost and may increase supply; a flood may reduce it despite unchanged product price.

A product’s own price is not a non-price determinant.

Prices of related goods can shift supply through competitive or joint production. If farmland can produce wheat or maize, a higher maize price may reduce wheat supply (competitive supply); if beef and leather are produced together, more beef production can increase leather supply (joint supply). Expected higher future prices may reduce current supply, while entry of firms shifts market supply right and exit shifts it left.

A movement along supply follows a change in the good’s own price; a shift follows a change in another supply determinant.

Confusing these changes reverses the diagram and the causal explanation.

Ask whether the good’s own price changed; if not, examine costs, technology, taxes, expectations or firms.

A rise in the market price moves up the curve; a cheaper battery shifts the supply of electric vehicles right.

A change in quantity supplied is not the same as a change in supply.

Market equilibrium is the price and quantity at which quantity demanded equals quantity supplied. No surplus or shortage pushes the market away from that point.

At a price above equilibrium, surplus pressures sellers to reduce price; below it, shortage pressures buyers to bid price up.

Locate the intersection, compare actual price with equilibrium and identify surplus or shortage.

Demand and supply meet at $6 and 100 units; at$8, firms offer more than buyers want, creating surplus.

Equilibrium is a tendency under stated conditions, not proof that every buyer is satisfied.

A change in a demand or supply determinant shifts a curve and creates a new equilibrium price and quantity.

The direction depends on which curve shifts and whether the movement changes price, quantity or both.

Name the shift, predict the new intersection and explain the adjustment path.

A heatwave shifts demand for cold drinks right, raising equilibrium price and quantity if supply slopes upward.

Do not shift a curve for a change in the good’s own price.

After a rightward demand shift, the old price creates excess demand because $Q_d>Q_s$; competition among buyers raises price, quantity supplied expands along supply and quantity demanded contracts along the new demand curve until a new equilibrium is reached. After a rightward supply shift, the old price creates excess supply because $Q_s>Q_d$; sellers reduce price until the new intersection is reached. State both the initial disequilibrium and adjustment, not only the final arrows.

The price mechanism uses price signals, incentives and rationing to coordinate scarce resources in markets.

Prices communicate relative scarcity, reward suppliers and ration demand, but may exclude people with low income or ignore external costs.

Trace how a change in demand or supply changes price and the resulting behaviour.

A shortage of rental homes raises rents, encouraging construction but making access harder for some households.

The price mechanism coordinates allocation, not necessarily fairness or social welfare.

Consumer surplus is willingness to pay minus price; producer surplus is price minus willingness to accept. They measure gains from voluntary exchange.

Surplus changes when price, quantity or curve position changes, and distribution matters even when total surplus rises.

Mark the relevant area between price and demand or supply, then state who gains or loses.

If a buyer would pay $10 but pays$7, consumer surplus is $3 for that unit.

Surplus is not cash profit or a complete measure of wellbeing.

Allocative efficiency occurs when resources produce the combination most valued by society, represented in a competitive model by price equal to marginal cost.

At the efficient quantity, total surplus is maximised under the model assumptions. Market power, externalities and missing markets can cause failure.

Compare marginal benefit and marginal cost, then identify the source of any welfare loss.

If the marginal benefit of the last unit is $5 and marginal cost$5, producing one more would not increase net benefit.

A competitive equilibrium is not automatically socially efficient when external costs exist.

Surplus can be calculated as geometric areas: triangle area is one-half × base × height, using the relevant price and quantity differences.

The diagram must identify intercepts, equilibrium and the actual price; a policy can transfer surplus or create deadweight loss.

Label axes and vertices, calculate each area, then compare total and distributional change.

A consumer-surplus triangle with base 100 units and height $4 has area$200.

Do not use a rectangle when the demand or supply boundary is sloped.

The rational-choice benchmark assumes consumers are rational, maximize utility and possess perfect information. Behavioural economics asks how real decisions depart systematically from those assumptions.

Rules of thumb simplify choices; anchoring makes an initial value influential; framing changes responses when equivalent options are presented differently; availability bias overweights vivid or recent examples. Imperfect information further weakens informed maximization.

Bounded rationality limits processing, bounded self-control creates conflict between current and long-term preferences, and bounded selfishness allows fairness or concern for others. Identify the specific limit and explain how it changes the predicted choice.

A shopper may treat a crossed-out 'original price' as an anchor and judge the current price as a bargain without comparing alternatives, contradicting perfect-information utility maximization.

Indifference curves and budget-line optimization are not required in this syllabus Objective. A bias is a systematic tendency, not proof that every consumer always makes the same error.

Choice architecture is the way options are organized. Defaults apply unless a person opts out; restricted choices remove some options; mandated choices require an active selection rather than allowing no decision.

Nudge theory uses predictable behavioural responses—such as inertia, salience or framing—to steer choices while normally preserving freedom to choose. The architecture changes the decision context rather than the underlying prices or available information alone.

Identify the target behaviour, the architecture used and whether alternatives remain available; then evaluate effectiveness, transparency, autonomy and distributional effects.

Automatic pension enrolment with an opt-out default can raise participation because inertia favours staying enrolled. Requiring every employee to select yes or no is a mandated choice instead.

A nudge is not automatically a restriction or mandate, and a default does not eliminate choice. Bias definitions belong to Objective 2.4.1; this card focuses on applying behavioural insights.

Businesses may pursue profit maximisation, revenue growth, market share, survival, social or environmental goals; the objective shapes decisions and trade-offs.

Objectives can conflict across time and stakeholders. A firm may accept lower short-run profit to build capacity or meet a social mission.

State the objective, time horizon and constraint before evaluating a decision.

A start-up prioritises survival and cash flow over current profit while building a customer base.

“Businesses maximise profit” is a model assumption, not a universal fact.

Profit maximization selects the output or strategy expected to generate the greatest profit. Alternatives change the decision rule: corporate social responsibility considers social and environmental stakeholders; market-share objectives prioritize sales relative to rivals; satisficing seeks an acceptable rather than maximum outcome under constraints; growth expands scale or reach. A firm can combine objectives, but conflicts require an explicit priority and time horizon.

Elasticity measures percentage responsiveness.

Elasticity compares a percentage change in one variable with a percentage change in another, so it is unit-free and comparable across scales.

Example

A 5% price rise causing a 10% fall in quantity gives |PED|=2, indicating elastic demand.

Write the percentage changes first, then interpret magnitude and sign in the decision context.

Elasticity is not the same as slope; percentage bases and the chosen interval matter.

Relative elasticity compares percentage quantity responses for a given percentage change in the causal variable. On demand diagrams drawn with the same axis scales and from a common point, a flatter curve is relatively more price elastic and a steeper curve relatively less elastic—but elasticity is not identical to visual slope, so calculate when data are provided.

$PED=(\%\Delta Q_d)/(\%\Delta P)$. It is normally negative because price and quantity demanded move oppositely; many decisions use the absolute magnitude while retaining the sign when asked.

Calculate each percentage change using the base specified by the data or examination convention, divide, and classify: $|PED|<1$ inelastic, $=1$ unit elastic, and $>1$ elastic. The theoretical magnitude ranges from zero to infinity.

Example

If price rises from $10 to$11, the percentage price change is $10\%$. If quantity demanded falls from 200 to 170, the percentage quantity change is $-15\%$. Thus $PED=-15\%/10\%=-1.5$, so demand is elastic.

State the sign convention and calculation base. Midpoint reasoning appears only in local HL evidence and is not inserted into this shared SL/HL card unless the question explicitly supplies that convention.

PED is measured over a stated price interval and market definition; it can change at another point on the same curve.

PED predicts how a price change affects total revenue.

When demand is elastic, quantity changes proportionally more than price; when inelastic, price changes dominate revenue.

Example

A 10% price rise with a 20% quantity fall reduces revenue because the 2× quantity response outweighs price.

Compare percentage changes rather than assuming every price rise raises revenue.

The unit-elastic case leaves revenue approximately unchanged only under the stated local conditions.

Classification and revenue map using $|PED|$: perfectly inelastic $=0$ (vertical), inelastic $0<|PED|<1$, unit elastic $=1$, elastic $|PED|>1$, and perfectly elastic tends to infinity (horizontal). If demand is elastic, price and total revenue move in opposite directions; if inelastic, they move together; at unit elasticity, a small price change leaves total revenue unchanged.

Elasticity varies along a straight-line demand curve.

Slope is constant on a straight line but elasticity uses relative percentage changes, so it is more elastic near the price intercept and less elastic near the quantity intercept.

Example

The same one-unit price movement can represent a large percentage quantity change at one point and a small one elsewhere.

Read the point on the curve before predicting revenue or responsiveness.

Do not infer constant elasticity from a constant slope.

Determinants of PED explain why buyers respond differently.

Substitutes, necessity, habit, budget share and time affect how easily consumers can change quantity demanded after a price change.

Example

A branded medicine may have inelastic short-run demand but become more elastic when substitutes or time to adjust increase.

Name the determinant and the direction of its effect before assigning an elasticity.

These are tendencies, not universal values; market segment and time horizon matter.

Four syllabus determinants: more and closer substitutes make demand more elastic; greater necessity makes it more inelastic; a larger proportion of income makes it more elastic; and more adjustment time usually makes it more elastic. Firms use PED for pricing and revenue forecasts, while governments use it to anticipate tax effects on consumption and revenue. Apply tendencies to a defined market and time period.

Demand for primary commodities is generally more price inelastic than demand for manufactured products: a percentage price change tends to cause a smaller percentage change in commodity quantity demanded.

Primary inputs may be necessary for production, form a small share of the final product's price and have few close short-run substitutes. Manufactured products are often more differentiated and face more brands, models or alternative goods, making substitution easier.

Example

A food manufacturer may keep buying nearly the same quantity of a basic grain after a moderate price rise because reformulating production takes time, while consumers can switch more readily between competing manufactured snack brands.

This is a general tendency, not a rule for every product. Market definition, available substitutes, income share and time can make a particular commodity elastic or a manufactured good inelastic.

Do not infer export-revenue volatility without separately analysing supply shifts, PED and the percentage price and quantity changes.

Income elasticity classifies demand across the income cycle.

YED=% change in quantity demanded/% change in income; positive values indicate normal goods and negative values inferior goods.

Example

If income rises 8% and demand for restaurant meals rises 12%, YED=1.5, a normal income-elastic good.

State the sign and magnitude, then connect it to forecasting or consumption patterns.

YED can differ across households and income ranges; it is not a permanent label for a product.

YED classes: $YED<0$ inferior; $0<YED<1$ normal and income-inelastic, commonly necessities; $YED>1$ normal and income-elastic, commonly services or luxuries. An Engel curve plots income vertically or horizontally as labelled against quantity demanded: necessities rise less than proportionately, luxuries more than proportionately, and inferior-good demand falls over the relevant income range. Rearrange the formula to find a missing percentage change.

YED helps firms plan for changing incomes.

Firms use income responsiveness to anticipate which products expand or contract during booms and downturns, alongside costs and competition.

Example

A premium travel firm with high positive YED may see demand fall faster than income during a recession.

Combine the elasticity estimate with the expected income change and the firm’s product mix.

Forecasting from YED assumes other major determinants do not shift at the same time.

YED also explains sectoral change: as average incomes rise, demand tends to grow less than proportionately for necessities and more than proportionately for income-elastic services and luxuries, shifting employment and output toward those sectors. Firms combine estimated YED with an income forecast to plan capacity, product mix and risk; coefficients can change across income ranges and over time.

$PES=(\%\Delta Q_s)/(\%\Delta P)$. Price and quantity supplied normally move together, so PES is non-negative and its theoretical range is from zero to infinity.

Calculate both percentage changes with a consistent base, divide and classify: $0<PES<1$ inelastic, $PES=1$ unit elastic and $PES>1$ elastic. Rearrange $\%\Delta Q_s=PES\times\%\Delta P$ to find a missing response.

Example

If price rises by $10\%$ and quantity supplied rises by $5\%$, $PES=5\%/10\%=0.5$, so supply is price inelastic over that period. If $PES=1.4$ and price rises $5\%$, quantity supplied is predicted to rise $7\%$.

PES is a percentage responsiveness, not slope, and applies to a stated market, interval and time horizon. The determinants explaining its value belong to Objective 2.6.2.

Always interpret both the coefficient and the production time period.

PES diagrams show how quantity supplied responds to price; determinants include time, spare capacity, stocks, mobility of factors and production complexity.

The same firm may have inelastic short-run supply and elastic long-run supply as capacity changes.

A farmer cannot increase harvest this week, but can plant more next season.

A flatter curve is a modelled response, not a guarantee for every range.

Apply PES to a stated time horizon.

PES classification: perfectly inelastic $PES=0$ is vertical; inelastic $0<PES<1$; unit elastic $PES=1$; elastic $PES>1$; perfectly elastic tends to infinity and is horizontal. Determinants are time, mobility of factors, unused capacity, ability to store output and the rate at which costs rise as output expands. Compare curves only with the same axis scales and market definition.

Primary commodity supply is often inelastic in the short run because crops and extraction capacity take time to change.

Weather and harvest cycles can create price swings; storage and diversification can alter the response.

A frost cuts coffee supply before the next harvest, so price rises sharply.

Inelastic is period-specific, not permanent.

Apply PES to a stated time horizon.

Primary commodities generally have lower PES than manufactured products because biological growth and harvest seasons delay output, extraction or land capacity is difficult to expand, commodities may be perishable or costly to store, and specialized factors are less mobile. Manufacturers can often hold inventories, add shifts or redirect inputs more quickly. These are tendencies that depend on the stated time horizon.

Governments intervene when markets fail to achieve efficiency, equity, stability or other social objectives.

Externalities, public goods, information gaps, market power and inequality can create a case, but intervention has administrative and unintended costs.

Name the market failure or objective and identify who gains, loses and bears the cost.

A pollution tax targets an external cost; a transfer payment targets income inequality.

A market outcome is not automatically a failure just because it is unequal.

The syllabus reasons are to earn government revenue, support firms, support low-income households, influence production, influence consumption, correct market failure and promote equity. Match the reason to the tool: an indirect tax may raise revenue or discourage consumption; a subsidy may support firms or encourage output; direct provision or a price policy may improve access. Do not assume one intervention serves every objective equally well.

Taxes, subsidies, price controls, regulation, public provision and information policies change incentives, costs, access or rights.

The tool must match the problem: a subsidy may increase consumption but also cost public funds; a regulation may work only if enforced.

Trace the policy through demand/supply or behaviour, then state the implementation condition.

A maximum price below equilibrium can improve affordability for some but create a shortage.

Naming a policy is not evaluating its mechanism.

Complete tool map: a binding price ceiling lies below equilibrium; a binding price floor lies above it; indirect taxes create a wedge and shift supply upward/left; subsidies lower effective producer costs and shift supply downward/right; direct provision supplies services publicly; command-and-control regulation sets required or prohibited behaviour, enforced through legislation. Label stakeholder prices and quantities on each diagram.

Intervention can change price, quantity, surplus, government revenue, inequality and deadweight loss.

Incidence depends on elasticities and enforcement; intended and unintended effects may differ across groups and time.

Map the new outcome and compare efficiency, equity and feasibility.

A per-unit tax raises buyer and seller prices differently depending on relative elasticity.

A policy can improve one objective while worsening another.

A nudge changes choice architecture without banning options or substantially changing prices, using defaults, salience or framing.

Nudges rely on predictable behavioural tendencies and should be transparent, easy to opt out of and tested for distributional effects.

Identify the default or frame, the behaviour it targets and the ethical trade-off.

Making healthy food the default side dish increases uptake while leaving alternatives available.

A nudge is not coercion and does not solve every information or income constraint.

Intervention diagrams and calculations quantify changes in price, quantity, revenue, surplus, tax receipts or welfare loss.

Correct areas and incidence require labelled axes, intercepts and the policy wedge or constraint.

Draw the policy, calculate the relevant rectangle or triangle and interpret the distribution.

A $2 tax on 1,000 units raises$2,000 gross revenue before administration costs.

A geometric result is not a complete welfare evaluation.

Calculation workflow: for a ceiling or floor, read $Q_d$ and $Q_s$ at the controlled price and compute shortage $Q_d-Q_s$ or surplus $Q_s-Q_d$. For a per-unit tax, the wedge is buyer price minus seller price; tax revenue is tax per unit $\times$ post-tax quantity. For a per-unit subsidy, government cost is subsidy per unit $\times$ post-subsidy quantity. Calculate consumer/producer surplus areas from labelled triangles or rectangles and compare with the original equilibrium.

Socially optimum output occurs where social marginal benefit equals social marginal cost, including relevant external benefits or costs.

The market outcome can overproduce a harmful good or underproduce a beneficial one when private incentives omit spillovers.

Compare private and social marginal curves and identify the welfare-maximising quantity.

If pollution adds $2 social cost per unit, social marginal cost lies above private cost and the optimum quantity is lower.

Optimum depends on the objectives, evidence and valuation used.

At $MSB=MSC$, the marginal social gain from the last unit equals its marginal social opportunity cost, so producing more would add more social cost than benefit and producing less would forgo net benefit. Under the model, this quantity is allocatively efficient and maximizes social/community surplus. Do not substitute private demand or supply for MSB or MSC when an externality separates them.

An externality is an uncompensated cost or benefit affecting a third party. The market quantity differs from the social optimum because decision-makers use private rather than social marginal costs or benefits.

Negative production: $MSC>MPC$, causing overproduction. Negative consumption: $MSB<MPB$, causing overconsumption. Positive production: $MSC<MPC$, causing underproduction. Positive consumption: $MSB>MPB$, causing underconsumption. Welfare loss lies between the relevant social curves over the misallocated units.

First identify production versus consumption and cost versus benefit; then choose which marginal curve separates, mark market and social quantities, and shade the welfare-loss region with arrows toward the efficient quantity.

Factory pollution is a negative production externality, so supply based on $MPC$ gives output above the $MSB=MSC$ optimum. Vaccination benefits others through consumption, so demand based on $MPB$ gives output below the optimum.

Merit goods are judged socially under-consumed and commonly linked to positive consumption externalities; demerit goods are judged over-consumed and commonly linked to negative consumption externalities. These judgments also involve information and values.

Deadweight loss is the lost net surplus from units produced or consumed away from the socially efficient quantity, often a triangle on a diagram.

Use the base of quantity difference and height of marginal-cost/benefit wedge, with correct axes and units.

Label efficient and market quantities, calculate one-half×base×height and interpret who loses.

If five excess units have a $4 average wedge, deadweight loss is$10.

The triangle is a model estimate, not a complete measure of human harm.

A common pool resource is rival but difficult to exclude users from, so individual extraction can deplete the shared stock.

Open access creates a “tragedy of the commons” when users ignore the cost imposed on others and future users.

Identify rivalry, exclusion difficulty and the governance rule that could protect the stock.

An open fishery may be overharvested because each boat gains while depletion is shared.

Common pool is not the same as a public good: rivalry matters.

Responses include Pigouvian or carbon taxes, subsidies, legislation and regulation, education, tradable permits, international agreements, collective self-governance and government provision. Each changes prices, information, rights, quantities or governance differently.

A tax can move private cost toward social cost; a subsidy can encourage an external benefit; permits cap total pollution and allow trading; regulation sets limits; education changes information; provision supplies the beneficial output; commons governance creates monitored access and shared rules.

Match the instrument to whether the failure is an external cost, external benefit or open-access depletion. On a carbon-tax diagram, shift supply/MPC upward by the tax toward MSC, raising price and reducing polluting output toward the social optimum.

A fishery may combine a monitored community quota with an international agreement when stocks cross borders. A subsidy for vaccination targets under-consumption from external benefit, while a carbon tax targets excessive polluting production.

Property rights or quotas alone are not the complete syllabus response set. Every policy depends on measurement, enforcement and stakeholder legitimacy and may create equity or administrative costs.

Policy evaluation compares effectiveness, efficiency, equity, administrative feasibility, unintended effects and sustainability.

A policy can meet its target at high cost or shift harm to another group or place; outcomes should be measured against a counterfactual where possible.

State the criterion, evidence and trade-off before recommending or rejecting a policy.

A carbon tax cuts emissions but burdens low-income households unless revenue is recycled or alternatives are available.

Evaluation is not a list of pros and cons without a clear objective.

For each policy, evaluate how accurately the externality can be measured, whether the intervention changes behaviour, administrative and enforcement costs, evasion and consequences for consumers, producers, government and third parties. Global sustainability problems cross borders, so international agreements can prevent free-riding or leakage, but differences in incentives, monitoring capacity and enforcement make cooperation difficult.

A pure public good is non-rival and non-excludable.

These properties create free riding; many real goods are mixed.

Test rivalry and exclusion separately before classifying.

National defence protects residents together; a crowded park is rival at capacity.

Publicly provided does not automatically mean public good.

Non-rivalry means one person's use does not reduce the amount available to others; non-excludability means non-payers cannot feasibly be prevented from benefiting. Because each person can wait for others to pay, stated willingness to pay is understated and a profit-seeking market cannot reliably collect enough revenue, causing non-provision or under-provision relative to the efficient quantity.

Government intervention addresses free riding by using compulsory revenue such as taxation to finance provision. It may directly provide the public good through public agencies or contract production to a private firm.

Direct provision combines public funding and public production. Contracting out keeps collective funding and service requirements public but uses a private supplier selected and monitored under a contract.

Compare cost, expertise, service quality, coverage, accountability and monitoring. The government must specify outputs and enforce the contract because users cannot rely on ordinary individual purchasing to reveal demand.

A municipality can operate street lighting itself or pay a private company to install and maintain it, while residents receive the shared service without individual usage charges.

Public funding does not require public production, and private production does not turn a non-rival, non-excludable service into a private good. Neither delivery method is automatically efficient or equitable.

Asymmetric information exists when one side knows more relevant information than the other. It can cause adverse selection before agreement or moral hazard after agreement.

Hidden quality can drive good products out; hidden actions can shift risk to others.

Identify who knows what and when the gap occurs.

Used-car sellers know quality better than buyers, so low offers may drive good cars out.

An information gap is not automatically harmful if contracts solve it.

Government responses are legislation, regulation and provision of information. Private responses are signalling by the informed party and screening by the less-informed party.

Legislation can require disclosure or prohibit misleading conduct; regulation sets and enforces standards; public information makes quality or risk easier to compare. A credible signal separates types because it is harder for a low-quality party to imitate, while screening offers tests or contract choices that induce parties to reveal information.

For hidden quality before agreement, ask whether disclosure, a signal or screening can improve selection. For hidden action after agreement, ask whether rules and monitoring change incentives without creating excessive cost or exclusion.

A qualified worker signals ability with a verifiable credential. An insurer screens applicants using relevant risk information or a menu of deductibles, while regulation controls what information may be requested and requires truthful disclosure.

Warranties or certification can be examples only when their signalling or regulatory mechanism is explicit. More information is not enough if it is unreliable, unusable or costly, and screening can create equity or privacy concerns.

Market structures compare how firms face competition.

Start with the number of firms, product similarity, entry barriers and information; these features determine the market model before any diagram is drawn.

Example

A local bakery market has many sellers and differentiated products, while a regulated electricity grid has few suppliers and high entry costs.

Classify the structure from evidence, then predict pricing power, output and efficiency.

A label such as ‘large firm’ does not by itself prove monopoly power; contestability and substitutes still matter.

Structure map: perfect competition—many firms, free entry, homogeneous product; monopoly—single or dominant firm, high entry barriers, no close substitutes; oligopoly—few large firms, high barriers and strategic interdependence; monopolistic competition—many firms, free entry and differentiated products. Classify from the full feature set, not firm size alone.

A rational producer compares marginal benefit with marginal cost.

Profit is maximized where the next unit adds no more revenue than cost, subject to the firm’s demand, technology and legal constraints.

Example

If a firm’s marginal revenue is $12 and marginal cost is$9 at the current output, expanding output can raise profit until the comparison reverses.

Use MR=MC as a decision rule, then check whether the firm can actually sell the extra output.

Rational behaviour is a model assumption, not a claim that every manager has perfect information or identical goals.

Profit $=TR-TC$. Marginal values are changes per extra unit: $MR=\Delta TR/\Delta Q$ and $MC=\Delta TC/\Delta Q$; profit is maximized where $MC=MR$ with MC rising through MR. At that output, $AR>AC$ gives abnormal profit, $AR=AC$ normal profit and $AR<AC$ a loss; total profit is $(AR-AC)\times Q$. Calculate $AR=TR/Q$ and $AC=TC/Q$ from data when needed.

Market power is the ability to influence price. A perfectly competitive firm is a price taker, so market price fixes a horizontal firm curve $P=D=AR=MR$; imperfectly competitive firms face downward-sloping demand and have varying price-making power.

The competitive firm maximizes profit where rising $MC=MR=P$. At that output, $AR>AC$ gives abnormal profit, $AR=AC$ normal profit and $AR<AC$ a loss in the short run. Free entry and exit remove abnormal profit in long-run equilibrium.

Efficiency

The competitive market is allocatively efficient when $P=MC$, equivalently $MB=MC$, so community surplus is maximized under the model. Label the market equilibrium separately from the individual firm's horizontal demand curve.

Do not use a monopoly patent example to teach the perfect-competition Objective. Price-taking requires the market assumptions, and $MC=MR$ identifies output while AR versus AC identifies profit.

A high market share can be temporary; evidence of barriers and switching costs is needed before inferring durable power.

A monopoly faces the market demand curve.

With one dominant supplier, the firm chooses output where MR=MC and then reads the highest price buyers will pay from demand.

Example

If demand is P=20−Q and MC=4, the profit-maximizing output solves MR=4, then price is found from demand rather than set equal to MC.

Separate the output decision from the price read-off, and compare the result with the competitive benchmark.

A monopoly is not automatically a public firm, and natural monopoly conditions depend on cost structure, not simply on being the only seller.

A monopolist maximizes at $MR=MC$ and reads price from AR/demand. If $P=AR>MC$, output is below and price above the competitive $P=MC$ quantity, creating allocative inefficiency and welfare loss. Abnormal profit, normal profit or loss depends on AR relative to AC at that output. A natural monopoly has falling average cost across the relevant market demand because one large supplier can exploit economies of scale more cheaply than multiple firms.

Oligopoly decisions are interdependent.

A few firms must anticipate rivals’ reactions, so price, advertising and output choices can create strategic outcomes rather than a single independent optimum.

Example

If one airline cuts fares, competitors may match the cut; the first firm’s gain depends on the response, not only on its own demand curve.

State each firm’s action, expected response and resulting payoff before judging cooperation or competition.

Oligopoly does not guarantee collusion; outcomes range from aggressive rivalry to tacit coordination and depend on evidence.

Collusive oligopolists coordinate and may act like a monopoly; non-collusive firms choose independently while anticipating rivals. Interdependence creates price-war risk, incentives to collude and incentives to cheat on an agreement. A payoff matrix records each firm's outcome for paired strategies and reveals dominant strategies or unstable cooperation. Firms use price and non-price competition. A concentration ratio is the combined market share of the largest stated number of firms; higher concentration suggests, but does not prove, greater power.

Monopolistic competition combines rivalry with product differentiation.

Many firms can enter, but branding or design gives each a downward-sloping demand curve and limited short-run price discretion.

Example

Two cafés may charge different prices because location and taste differentiate them, yet new cafés can enter if profits persist.

Link product differentiation to short-run power, then use entry to explain why long-run economic profit is pressured.

Product variety is not proof of perfect competition; each firm still faces its own demand and costs.

In both short and long run, choose $MR=MC$ output and read price from AR. Short-run entry barriers can permit abnormal profit, normal profit or loss. Free entry and exit shift each firm's demand until long-run normal profit where $AR=AC$ at the chosen output. Because product differentiation leaves downward-sloping AR, $P>MC$ and spare capacity imply allocative inefficiency; many substitutes make demand more elastic and inefficiency generally smaller than monopoly while variety is greater.

Market power can fund innovation but also create allocative loss.

The same barrier that supports research or network investment may let a firm restrict output, raise price or weaken consumer choice.

Example

A software platform may use profits to improve security while its closed ecosystem raises switching costs for users.

Evaluate both the dynamic benefit and the static cost, specifying who gains, over what time horizon and under which evidence.

There is no automatic sign for welfare: innovation claims need evidence, and deadweight loss is not the only criterion.

Government may use legislation and regulation, government ownership or fines when significant market power is abused. The objective is to constrain harmful conduct or outcomes rather than punish firm size by itself.

Legislation can prohibit collusion or anti-competitive exclusion; regulation can control price, quality or access; government ownership can place a natural-monopoly service under public control; fines deter and penalize proven breaches.

Example

A utility regulator may cap a natural monopoly's price and set service standards. Competition law may fine firms that coordinate prices, provided investigation establishes the prohibited conduct.

Evaluate enforcement cost, regulatory capture, information gaps, incentives to invest, service quality and consumer outcomes. Merger control or structural separation may be related policies, but the required syllabus responses are legislation/regulation, ownership and fines.

A policy that lowers price can also reduce investment or quality; the diagram alone cannot settle the evaluation.

Free markets can distribute gains unevenly.

Prices coordinate voluntary exchange, but initial assets, bargaining power, education and discrimination shape who receives income and opportunity.

Example

A rise in demand for a scarce skill can increase wages for trained workers while leaving others behind even as total output grows.

Separate efficiency from equity: identify the market outcome, then examine distribution and the policy trade-off.

‘Free’ does not mean fair or costless; externalities, unequal starting positions and missing markets can change the judgement.

In a circular-flow diagram, households supply labour, land, capital and entrepreneurship to firms and receive wages, rent, interest and profit; firms receive consumption spending in return for goods and services. Households owning more productive assets or scarce skills receive larger factor incomes, can save and acquire further wealth, and may pass advantages to later periods. Low-income households have less saving capacity and may rely mainly on lower-paid labour, so the free-market flow can reinforce unequal income and wealth even when markets clear.