Chapter 7: Demand and Supply Analysis
Part 7.1 – The Foundation of Microeconomics
By Dr. Anthony Fok
Introduction
Every day, millions of buyers and sellers interact in markets.
A student buys bubble tea after school.
A commuter books a Grab ride during the morning rush hour.
A family purchases groceries at a supermarket.
An investor buys shares on the Singapore Exchange (SGX).
Although these transactions involve different products and services, they are all governed by the same fundamental economic principle:
The interaction of demand and supply determines market prices and quantities.
Demand and supply is arguably the most important concept in Economics. Almost every topic in the A-Level Economics syllabus—including inflation, market failure, labour markets, international trade and government intervention—builds upon this foundation.
Mastering demand and supply will help you understand not only examination questions but also real-world events, such as:
- Why did egg prices rise during the COVID-19 pandemic?
- Why do ERP charges vary at different times of the day?
- Why do hotel prices increase during the Formula One Singapore Grand Prix?
- Why did COE prices reach record highs?
- Why do Grab fares increase during heavy rain?
In every case, the answer lies in changes in demand, supply, or both.
What Is Demand?
Demand refers to the quantity of a good or service that consumers are willing and able to purchase at different prices during a given period of time, ceteris paribus.
This definition contains several important ideas.
Demand is not simply a desire for a product.
Consumers must also possess the purchasing power to buy it.
For example:
A student may want to own a Ferrari.
However, if the student cannot afford it, this desire does not constitute effective demand.
Economists therefore define demand as both willingness and ability to pay.
Effective Demand
Only consumers who are both willing and financially able to purchase a product contribute to market demand.
Consider the following situations.
Example 1
A teenager wishes to buy the latest gaming laptop but has no money.
This is merely a desire.
It does not contribute to market demand.
Example 2
A working professional plans to purchase a new MacBook next month and has sufficient savings.
This represents effective demand.
The Law of Demand
One of the most fundamental principles in Economics is the Law of Demand.
It states:
As the price of a good falls, quantity demanded increases, ceteris paribus.
Conversely,
As the price of a good rises, quantity demanded decreases, ceteris paribus.
This inverse relationship exists because consumers respond to changes in prices.
Why Does the Law of Demand Hold?
There are three main reasons.
1. The Substitution Effect
When the price of a product falls, it becomes relatively cheaper compared with substitute goods.
Consumers therefore substitute towards the cheaper product.
Singapore Example
Suppose chicken becomes significantly cheaper than beef.
Some households purchase more chicken instead of beef.
Demand for chicken increases.
2. The Income Effect
A fall in price increases consumers’ real purchasing power.
Consumers can now afford to purchase more goods and services with the same income.
For example:
Suppose MRT fares decrease.
A commuter saves money each month.
The savings may be spent on coffee, entertainment or dining.
Consumers effectively become better off in real terms.
3. The Law of Diminishing Marginal Utility
Consumers derive satisfaction (utility) from consumption.
However, each additional unit consumed generally provides less additional satisfaction than the previous one.
Consequently, consumers are willing to purchase additional units only if prices fall.
For example:
The first slice of pizza provides significant satisfaction.
The second slice remains enjoyable.
By the sixth slice, additional satisfaction is much smaller.
Consumers therefore require lower prices before purchasing more.
Demand Schedule
A demand schedule illustrates the relationship between price and quantity demanded.
| Price (S$) | Quantity Demanded |
|---|---|
| 10 | 100 |
| 8 | 130 |
| 6 | 170 |
| 4 | 230 |
| 2 | 320 |
As price decreases, quantity demanded increases.
This illustrates the Law of Demand.
Demand Curve
The demand curve is a graphical representation of the demand schedule.
It slopes downward from left to right.
The downward slope reflects the inverse relationship between price and quantity demanded.
Students should always label:
- Price (vertical axis)
- Quantity (horizontal axis)
Proper diagram labelling is essential in examinations.
Individual Demand and Market Demand
Economists distinguish between individual demand and market demand.
Individual Demand
Individual demand refers to the quantity demanded by a single consumer.
For example:
One student purchases two cups of bubble tea each week.
Market Demand
Market demand is the sum of all individual demand within a market.
For example:
The total weekly demand for bubble tea in Singapore represents market demand.
Businesses focus primarily on market demand because it determines potential sales.
What Is Supply?
Supply refers to the quantity of a good or service that producers are willing and able to sell at different prices during a given period of time, ceteris paribus.
Like demand, supply involves both willingness and ability.
A producer may wish to supply more products but lack sufficient workers or machinery.
In such cases, actual supply is constrained.
The Law of Supply
The Law of Supply states:
As price increases, quantity supplied increases, ceteris paribus.
Conversely,
As price decreases, quantity supplied decreases.
This positive relationship exists because higher prices generally increase profitability.
Firms therefore have greater incentives to produce.
Why Does the Law of Supply Hold?
Several factors explain this relationship.
Profit Incentives
Higher prices increase potential revenue.
If production costs remain unchanged, profits increase.
Firms therefore expand production.
New Producers Enter the Market
Higher profits attract new firms.
Increased entry raises market supply over time.
Expansion of Existing Firms
Existing producers may:
- hire more workers,
- purchase additional machinery,
- increase operating hours,
- expand production capacity.
Higher prices encourage greater output.
Supply Schedule
| Price (S$) | Quantity Supplied |
|---|---|
| 2 | 60 |
| 4 | 110 |
| 6 | 180 |
| 8 | 250 |
| 10 | 340 |
As price increases, quantity supplied also increases.
Supply Curve
The supply curve slopes upward from left to right.
The upward slope reflects the positive relationship between price and quantity supplied.
Again, students should label:
- Price (vertical axis)
- Quantity (horizontal axis)
Singapore Example: COE Market
The Certificate of Entitlement (COE) system illustrates the interaction of demand and supply.
Demand for COEs increases when:
- household incomes rise,
- consumers expect future price increases,
- more people wish to own cars.
Supply of COEs, however, is largely determined by government policy and vehicle deregistration rates.
When demand rises faster than supply, COE premiums increase significantly.
This real-world example demonstrates the importance of understanding market equilibrium.
Dr. Anthony Fok’s Exam Tip
Students frequently confuse:
Demand
with
Quantity Demanded
Remember:
Demand refers to the entire demand relationship or curve.
Quantity demanded refers to one specific point on the demand curve resulting from a price change.
This distinction is heavily tested in examinations.
Common Student Mistake
❌ “When income increases, quantity demanded increases.”
Incorrect.
An increase in income causes demand to increase (the demand curve shifts to the right).
A change in quantity demanded occurs only because of a change in the product’s own price.
Understanding this distinction is essential for scoring full marks.
Quick Revision Summary
You should now be able to:
✓ Define demand and supply accurately.
✓ Explain the Law of Demand.
✓ Explain the Law of Supply.
✓ Distinguish between effective demand and desire.
✓ Draw demand and supply curves correctly.
✓ Differentiate individual demand from market demand.
✓ Apply demand and supply concepts to Singapore examples.
Coming Up in Part 7.2
In the next section, we will examine:
- Determinants of demand.
- Determinants of supply.
- Movements along curves versus shifts of curves.
- Changes in market demand and market supply.
- Singapore case studies.
- Examination techniques.