The Theory of Demand

Demand is a fundamental concept in Economics, representing the desire of a consumer to purchase goods and services and their willingness to pay a price for them. For demand to be 'effective,' it must be backed by the ability to pay (purchasing power).

1. Meaning and Determinants of Demand

The Law of Demand states that, ceteris paribus (all other things being equal), the higher the price of a commodity, the lower the quantity demanded, and vice versa. Factors that influence demand include:

• Price of the commodity: The most significant factor.
• Income of the consumer: For normal goods, demand rises with income. For inferior goods, demand falls as income rises.
• Prices of related goods: These include substitutes (e.g., Coke and Pepsi) and complements (e.g., cars and petrol).
• Tastes and Preferences: Changes in fashion or habits.
• Population size: A larger population generally leads to higher demand.
• Expectation of future price changes: If prices are expected to rise, current demand increases.

2. Demand Schedules and Curves

A Demand Schedule is a table showing the relationship between the price of a good and the quantity demanded. A Demand Curve is a graphical representation of this schedule, typically sloping downward from left to right (negative slope).

3. Change in Quantity Demanded vs. Change in Demand

• Change in Quantity Demanded: This is a movement along the same demand curve caused solely by a change in the price of the commodity. It results in expansion or contraction.
• Change in Demand: This is a shift of the entire demand curve (to the right or left) caused by factors other than the price of the commodity itself, such as income or tastes.

4. Types of Demand

• Derived Demand: Demand for a factor of production (e.g., demand for labor is derived from the demand for the goods labor produces).
• Composite Demand: Demand for a commodity that has multiple uses (e.g., electricity for lighting, cooking, and heating).
• Joint (Complementary) Demand: Demand for goods that are used together (e.g., camera and film, bread and butter).
• Competitive Demand: Demand for goods that serve as substitutes (e.g., beef and fish).

5. Elasticity of Demand

Elasticity measures the responsiveness of quantity demanded to changes in determinants.

• Price Elasticity (PED): (% Change in Quantity Demanded) / (% Change in Price).
• Income Elasticity (YED): (% Change in Quantity Demanded) / (% Change in Income).
• Cross Elasticity (XED): (% Change in Quantity Demanded of Good A) / (% Change in Price of Good B).

6. Importance of Elasticity

Elasticity helps producers determine pricing strategies, governments decide which goods to tax (inelastic goods are taxed more), and consumers understand market shifts.