This is the canonical source for Topic 2.1. The portal lesson should reveal the material in stages, with diagrams and classification tasks embedded throughout.

Official syllabus coverage

Students must understand:

• 2.1.1 effective demand;
• 2.1.2 individual and market demand and supply;
• 2.1.3 determinants of demand;
• 2.1.4 determinants of supply;
• 2.1.5 causes of a shift in the demand curve;
• 2.1.6 causes of a shift in the supply curve;
• 2.1.7 the distinction between a shift of a demand or supply curve and a

movement along these curves.

Product mastery map

The topic is tracked through seven portal skills:

1. effective demand;
2. individual and market demand;
3. individual and market supply;
4. determinants and shifts of demand;
5. determinants and shifts of supply;
6. movements along demand and supply curves;
7. application of demand-and-supply diagrams to unfamiliar markets.

Topic overview

Demand shows how much consumers are willing and able to buy at different<br>prices. Supply shows how much producers are willing and able to sell at<br>different prices.

The key analytical distinction is:

A change in the product's own price causes a movement along a curve. A change<br>in any relevant non-price determinant causes the entire curve to shift.

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1. Effective demand

Examination-ready definition

Effective demand is a desire for a good or service that is supported by both<br>the willingness and the ability to pay for it.

A person may want a product without creating effective demand.

Example

A student may strongly want a £1000 laptop. If the student is unable to pay or borrow the money, the desire is not effective demand at that price.

Why the distinction matters

Market demand does not measure every want. It measures the quantities that consumers are willing and able to purchase at different prices over a stated period.

Core components

Effective demand requires:

• desire;
• willingness to buy;
• ability to pay;
• a particular price;
• a particular time period.

Common trap

Demand is not simply need.

A person may need housing or healthcare but may not have enough purchasing power to create the same market demand as a wealthier consumer.

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2. Demand

Definition

Demand is the quantity of a good or service that consumers are willing and<br>able to buy at each possible price during a given period of time, ceteris<br>paribus.

Quantity demanded

Quantity demanded is the amount consumers are willing and able to buy at one specific price.

Demand refers to the entire relationship between price and quantity demanded.

Law of demand

Ceteris paribus, as the price of a good rises, quantity demanded falls; as the<br>price falls, quantity demanded rises.

This is an inverse relationship.

Demand curve

A standard demand curve:

• has price on the vertical axis;
• has quantity demanded on the horizontal axis;
• slopes downward from left to right;
• is labelled D.

Use:

Why the demand curve slopes downward

1. Substitution effect

When a good becomes cheaper relative to substitutes, consumers may switch towards it.

Example:

Price of train travel falls relative to coach travel → some passengers switch<br>to trains → quantity demanded of train journeys rises.

2. Income effect

A lower price increases consumers' real purchasing power.

With the same money income, consumers can afford more of the product and/or other products.

3. Diminishing marginal benefit

Consumers may value additional units less highly than earlier units, so a lower price is needed to encourage the purchase of more units.

This idea is developed more fully at A Level.

Ceteris paribus assumption

The demand curve isolates the relationship between:

• the product's own price;
• quantity demanded.

Other determinants are assumed unchanged.

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3. Individual demand

Definition

Individual demand is the quantity of a product that one consumer is willing<br>and able to purchase at different prices during a given period.

Individual demand schedule

The schedule can be plotted to form the individual's demand curve.

Interpretation

At $6, Consumer A demands 3 units.

If price falls from $6 to $4, quantity demanded rises from 3 to 5 units. This is a movement along the same individual demand curve.

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4. Market demand

Definition

Market demand is the total quantity of a product that all consumers in the<br>market are willing and able to buy at each price during a given period.

Horizontal summation

Market demand is found by adding individual quantities demanded at each price.

At $6:

Market demand = 3 + 2 + 5 = 10 units.

Why market demand may change

Market demand can change because:

• an existing consumer changes quantity demanded due to price;
• consumers' incomes or preferences change;
• the number of consumers changes;
• prices of related goods change.

Individual versus market curve

A market demand curve generally lies farther to the right than an individual demand curve because it sums the quantities demanded by all consumers at each price.

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5. Determinants of demand

A determinant of demand is a factor other than the product's own price that changes how much consumers wish to purchase at every price.

5.1 Income

Normal goods

For a normal good:

Income rises → demand increases → demand curve shifts right.

Examples may include:

• restaurant meals;
• holidays;
• higher-quality clothing.

Inferior goods

For an inferior good:

Income rises → demand decreases → demand curve shifts left.

Possible examples:

• very low-cost transport;
• basic own-brand products;
• low-quality substitutes.

A good is not inherently inferior for every consumer. Classification depends on actual consumer behaviour.

5.2 Prices of substitute goods

Substitutes can be consumed in place of each other.

Examples:

• tea and coffee;
• train and coach travel;
• competing smartphone brands.

Chain:

Price of coffee rises → tea becomes relatively cheaper → demand for tea rises<br>→ tea demand curve shifts right.

5.3 Prices of complementary goods

Complements are consumed together.

Examples:

• cars and fuel;
• printers and ink;
• games consoles and games.

Chain:

Price of games consoles falls → more consoles purchased → demand for games<br>rises → games demand curve shifts right.

5.4 Tastes and preferences

Demand may change because of:

• fashion;
• health concerns;
• advertising;
• cultural change;
• environmental awareness;
• reviews or social media.

More favourable preferences shift demand right.

5.5 Expectations

Consumers may respond to expected future changes.

Examples:

• expected future price rise → current demand may increase;
• expected future income fall → current demand may decrease;
• expected shortage → current demand may rise.

The effect depends on whether consumers can buy now and store or bring forward consumption.

5.6 Number of buyers and population

More buyers normally increase market demand.

Possible causes:

• population growth;
• immigration;
• market expansion;
• demographic change.

5.7 Distribution of income

Even if total national income is unchanged, a redistribution of income may change demand for particular products because income groups have different spending patterns.

5.8 Seasonal and environmental factors

Examples:

• hot weather raises demand for cold drinks;
• cold weather raises demand for heating;
• festivals raise demand for particular products.

5.9 Government policy

Demand may be influenced through:

• indirect taxes;
• subsidies to consumers;
• regulation;
• information campaigns;
• legal restrictions.

Some policy effects operate through price and therefore create a movement along the curve; others alter non-price conditions and shift demand. The diagram must match the mechanism described.

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6. Increase and decrease in demand

Increase in demand

An increase in demand means consumers are willing and able to buy more at every price.

The demand curve shifts to the right, from D1 to D2.

Use:

Possible causes:

• higher income for a normal good;
• lower income for an inferior good;
• higher price of a substitute;
• lower price of a complement;
• more favourable tastes;
• greater number of buyers;
• expectation of higher future prices.

Decrease in demand

A decrease in demand means consumers are willing and able to buy less at every price.

The curve shifts left.

Possible causes are the reverse of those above.

Language

Correct:

• increase in demand;
• decrease in demand;
• shift right;
• shift left.

Avoid using "extension" or "contraction" for a curve shift. Those terms refer to movement along a curve.

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7. Movement along the demand curve

A change in the product's own price causes movement along the existing demand curve.

Extension in quantity demanded

Price falls → quantity demanded rises → movement down and right along D.

Contraction in quantity demanded

Price rises → quantity demanded falls → movement up and left along D.

Crucial distinction

• change in quantity demanded = movement along;
• change in demand = shift of the curve.

Use:

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8. Supply

Definition

Supply is the quantity of a good or service that producers are willing and<br>able to sell at each possible price during a given period, ceteris paribus.

Quantity supplied

Quantity supplied is the amount producers are willing and able to sell at one specific price.

Supply is the entire price-quantity relationship.

Law of supply

Ceteris paribus, as price rises, quantity supplied rises; as price falls,<br>quantity supplied falls.

This is a direct relationship.

Supply curve

A standard supply curve:

• has price on the vertical axis;
• has quantity supplied on the horizontal axis;
• slopes upward from left to right;
• is labelled S.

Use:

Why the supply curve slopes upward

A higher market price may:

• increase potential profit;
• make higher-cost production worthwhile;
• encourage firms to use overtime or additional capacity;
• attract output from alternative uses.

At lower prices, some production may not cover opportunity cost or marginal cost.

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9. Individual supply

Definition

Individual supply is the quantity that one producer is willing and able to<br>sell at different prices during a given period.

Individual supply schedule

The schedule can be plotted to form the firm's supply curve.

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10. Market supply

Definition

Market supply is the total quantity that all producers in a market are<br>willing and able to sell at each price during a given period.

Horizontal summation

At $8:

Market supply = 8 + 6 + 4 = 18 units.

An increase in the number of firms normally shifts market supply right.

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11. Determinants of supply

11.1 Costs of production

Costs include:

• wages;
• raw materials;
• energy;
• rent;
• transport;
• borrowing costs.

Chain:

Input costs fall → profit at each product price rises → firms are willing to<br>supply more → supply shifts right.

Higher costs shift supply left.

11.2 Productivity and technology

Better technology or productivity can reduce unit cost and allow more output from the same inputs.

Productivity rises → cost per unit may fall → supply increases.

11.3 Indirect taxes

A tax on production raises firms' costs.

Indirect tax rises → supply decreases → supply curve shifts left.

The exact treatment of taxes is developed later in Topic 3.2.

11.4 Subsidies

A subsidy reduces the net cost of production or increases revenue received by firms.

Subsidy rises → supply increases → curve shifts right.

11.5 Prices of related goods in production

Competitive supply

Goods compete for the same resources.

Example:

A farmer can use land for wheat or maize.

Price of maize rises → maize becomes more profitable → land moves from wheat<br>to maize → supply of wheat falls.

Joint supply

Two products are produced together.

Examples:

• beef and leather;
• crude oil and associated products.

Higher production of one may increase supply of the joint product.

11.6 Number of firms

More firms in the market generally increase market supply.

Firm exit decreases market supply.

11.7 Expectations

If firms expect a higher future price, they may reduce current supply by holding stocks, provided storage is possible.

Expectations can also encourage current production and investment, so the effect must be explained in context.

11.8 Natural factors

Supply may be affected by:

• weather;
• disease;
• natural disasters;
• harvest conditions;
• resource discoveries.

These are especially important for primary products.

11.9 Government regulation

Regulations may:

• raise compliance costs;
• restrict production;
• improve productivity or infrastructure;
• change the number of firms able to operate.

The direction depends on the policy.

11.10 Producer objectives

A change in objectives may influence willingness to supply at each price.

For example, a state enterprise may continue supplying output that a profit-maximising firm would reduce.

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12. Increase and decrease in supply

Increase in supply

An increase in supply means producers are willing and able to sell more at every price.

The supply curve shifts right, from S1 to S2.

Use:

Possible causes:

• lower input costs;
• better technology;
• higher productivity;
• lower indirect taxes;
• higher subsidies;
• more firms;
• favourable natural conditions.

Decrease in supply

A decrease in supply means less is supplied at every price.

The supply curve shifts left.

Possible causes include:

• higher costs;
• taxation;
• lower productivity;
• adverse weather;
• fewer firms;
• tighter regulation.

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13. Movement along the supply curve

A change in the product's own price causes movement along the existing supply curve.

Extension in quantity supplied

Price rises → quantity supplied rises → movement up and right along S.

Contraction in quantity supplied

Price falls → quantity supplied falls → movement down and left along S.

Crucial distinction

• change in quantity supplied = movement along;
• change in supply = shift of the curve.

Use:

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14. Complete movement-versus-shift framework

Decision rule

Ask:

Did the price of the product itself change, or did another condition change?

• own price → movement along;
• other determinant → shift.

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15. Simultaneous changes

A real market may experience several changes at the same time.

Example:

• consumer incomes rise;
• production costs rise.

This can shift demand right and supply left simultaneously.

The current topic focuses on identifying the separate curves correctly. The resulting equilibrium effects are developed in Topic 2.4.

Exam discipline

When several changes occur:

1. identify the demand-side event;
2. identify the supply-side event;
3. shift each curve separately;
4. do not treat the change as movement along unless the product's own price is

the original cause.

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16. Market applications

Restaurant meals

Demand may rise because of:

• higher income;
• favourable reviews;
• population growth.

Supply may fall because of:

• higher wages;
• higher food costs;
• tighter licensing rules.

Agricultural products

Demand may change due to:

• health preferences;
• population;
• prices of substitutes.

Supply may change due to:

• weather;
• fertiliser prices;
• technology;
• disease.

Foreign currency

Demand and supply curves can also be used for currencies. The application is studied in Topic 6.4.

Transport

Demand may depend on:

• income;
• price of fuel;
• price of alternative transport;
• employment patterns.

Supply may depend on:

• wage costs;
• energy prices;
• capacity;
• government subsidies.

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17. Common misconceptions and examination traps

Trap 1: Demand means desire

Demand must be effective: willingness and ability to pay.

Trap 2: Demand and quantity demanded are identical

Demand is the whole curve. Quantity demanded is one amount at one price.

Trap 3: A lower price shifts the demand curve right

A lower own price causes movement down the existing curve.

Trap 4: Higher income always increases demand

Not for inferior goods.

Trap 5: Higher price of a complement increases demand

It normally decreases demand for the related good.

Trap 6: Higher price of a substitute decreases demand

It normally increases demand for the other substitute.

Trap 7: Supply means stock

Stock is the amount physically available. Supply is the amount offered for sale at different prices during a period.

Trap 8: Supply and quantity supplied are identical

Supply is the whole curve; quantity supplied is one amount at one price.

Trap 9: Higher production costs cause movement along supply

Costs are a non-price determinant, so supply shifts.

Trap 10: A tax shifts demand

A tax on producers normally shifts supply. A tax on consumers may affect demand, but the mechanism and tax design must be specified.

Trap 11: Extension means a curve shift

Extension and contraction describe movements along curves.

Trap 12: Market demand is the average of individual demand

It is the sum of individual quantities at each price.

Trap 13: Market supply is the supply of the largest firm

It is the sum of all firms' quantities at each price.

Trap 14: A curve must always be straight

Straight lines are a simplification. The economic relationship matters more than exact artistic shape unless the question specifies otherwise.

Trap 15: Price is a determinant that shifts the curve

The product's own price is already represented on the axes and causes movement along the curve.

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18. Diagram-quality checklist

For every demand or supply diagram:

1. Put price on the vertical axis.
2. Put quantity on the horizontal axis.
3. Label curves D or S.
4. Use D1 and D2 or S1 and S2 for shifts.
5. Add a directional arrow.
6. State the determinant causing the change.
7. Distinguish movement from shift in writing.
8. Use ceteris paribus where relevant.

Diagram assets

• demand-curve-movement.png
• demand-shift-right.png
• supply-curve-movement.png
• supply-shift-right.png
• demand-movement-vs-shift.png
• supply-movement-vs-shift.png

These were created from image-generated textbook panels, then cropped, enlarged, corrected and manually inspected.

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19. Paper 1 technique

Typical tasks include:

• define effective demand;
• distinguish individual and market curves;
• add quantities to calculate market demand or supply;
• identify the correct curve shift;
• distinguish substitutes and complements;
• distinguish movement along from a shift;
• identify the determinant behind a scenario.

Fast MCQ method

1. Identify whether the question concerns demand or supply.
2. Identify the variable that changed.
3. Decide movement or shift.
4. Decide right or left.
5. Check whether the good is normal or inferior, substitute or complement.

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20. Paper 2 technique

Four-mark demand-shift answer

Question:

Explain how an increase in consumer income may affect demand for restaurant<br>meals. [4]

Model answer:

If restaurant meals are a normal good, higher income increases consumers'<br>willingness and ability to buy them. At every price, a greater quantity is<br>demanded, so the demand curve shifts to the right from D1 to D2. The size of<br>the shift depends on how strongly demand responds to income.

Four-mark supply-shift answer

Question:

Explain how a fall in energy prices may affect the supply of manufactured<br>goods. [4]

Model answer:

Energy is a cost of production. A fall in energy prices reduces firms' costs<br>and may increase profit at each product price. Producers are willing and able<br>to supply more at every price, so the supply curve shifts right from S1 to S2.

Six-mark distinction answer

Question:

Explain the difference between an increase in demand and an extension in<br>quantity demanded. [6]

Model answer:

An extension in quantity demanded is caused by a fall in the product's own<br>price and is shown by movement down and to the right along the existing demand<br>curve. An increase in demand is caused by a non-price determinant such as<br>higher income for a normal good or a rise in the price of a substitute. It is<br>shown by the entire demand curve shifting right, because more is demanded at<br>every price.

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21. Active recall

1. Define effective demand.
2. Define demand.
3. Define quantity demanded.
4. State the law of demand.
5. Why does the demand curve slope downward?
6. Define individual demand.
7. Define market demand.
8. How is market demand calculated?
9. List six determinants of demand.
10. Explain the effect of higher income on a normal good.
11. Explain the effect of higher income on an inferior good.
12. Explain the effect of a rise in the price of a substitute.
13. Explain the effect of a fall in the price of a complement.
14. Distinguish an increase in demand from an extension.
15. Define supply.
16. Define quantity supplied.
17. State the law of supply.
18. Why does a supply curve usually slope upward?
19. Define individual supply.
20. Define market supply.
21. How is market supply calculated?
22. List six determinants of supply.
23. Explain how lower costs affect supply.
24. Explain how technology affects supply.
25. Explain the effect of an indirect tax.
26. Explain the effect of a subsidy.
27. Distinguish an increase in supply from an extension.
28. What is competitive supply?
29. What is joint supply?
30. State the movement-versus-shift decision rule.

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22. One-minute revision

Demand

Willingness and ability to buy at different prices.

Effective demand

Desire backed by willingness and ability to pay.

Market demand

Sum of all individual quantities demanded at each price.

Supply

Willingness and ability to sell at different prices.

Market supply

Sum of all firms' quantities supplied at each price.

Demand movement

Own price changes.

Demand shift

Income, related prices, tastes, expectations or number of buyers changes.

Supply movement

Own price changes.

Supply shift

Costs, technology, taxes, subsidies, natural factors or number of firms changes.

Perfect exam sentence

A change in the product's own price causes a movement along the curve;<br>a change in another determinant shifts the entire curve.