Business Economics · Theory of Demand and Supply

Meaning and Determinants of Demand: CA Foundation Business Economics

Updated 1 October 2026 · Fact-checked

Demand is the quantity of a good a consumer is willing and able to buy at a given price in a given period. The law of demand says that, other things equal, price and quantity demanded move in opposite directions. To solve questions, identify whether price or another determinant changed.

Understand Meaning and Determinants of Demand

Demand is not just a wish to buy. It needs three things: willingness, ability to pay, and a specific price and time period. A person who wants a car but cannot pay for it creates no demand in the economic sense.

A demand schedule is a table showing the quantity demanded at different prices. An individual demand schedule is for one buyer. A market demand schedule is the sum of all buyers' quantities at each price. A demand curve is the graph of the schedule, with price on the vertical axis and quantity on the horizontal axis.

The law of demand says that, other things remaining the same, when the price of a good rises, quantity demanded falls, and when price falls, quantity demanded rises. So the demand curve usually slopes downward from left to right. The phrase 'other things remaining the same' (ceteris paribus) is the key condition.

Why does the curve slope downward? Common reasons are: the income effect (a lower price raises your real purchasing power), the substitution effect (a cheaper good replaces costlier alternatives), diminishing marginal utility (each extra unit gives less satisfaction, so you pay less for it), and new buyers entering the market at lower prices.

Price is only one influence. The determinants of demand are the other factors: the consumer's income, prices of related goods (substitutes and complements), tastes and preferences, expectations of future prices or income, and the number of buyers. For market demand, population, its age mix and income distribution also matter. A change in price moves you along the curve. A change in any other determinant shifts the whole curve.

Key formulas to remember

Demand function: Dx = f(Px, Py, Y, T, E, N); Px = own price, Py = price of related goods, Y = income, T = tastes, E = expectations, N = number of buyers.
Law of demand: Price ↑ ⇒ Quantity demanded ↓; Price ↓ ⇒ Quantity demanded ↑ (ceteris paribus); Holds only when other determinants stay constant. Demand curve slopes downward.
Market demand: Market demand at a price = Σ individual demands at that price; Add quantities horizontally at each price, not prices.
Normal good: Income ↑ ⇒ Demand ↑; For inferior goods, income rise lowers demand.
Substitutes and complements: Substitutes: Py ↑ ⇒ Dx ↑; Complements: Py ↑ ⇒ Dx ↓; Tea and coffee are substitutes. Car and petrol are complements.

How to solve Meaning and Determinants of Demand questions

Most MCQs on this topic test whether you can tell the cause of a change in demand and its direction. Use this routine.

1Read the statement and find what changed: the good's own price or some other factor.
2If the own price changed, the answer is a movement along the same demand curve (change in quantity demanded).
3If income, tastes, related-goods prices, expectations or number of buyers changed, the whole curve shifts (change in demand).
4Classify the good: normal or inferior, and for related goods, substitute or complement.
5Decide the direction: rightward shift is an increase in demand, leftward shift is a decrease.
6For market demand sums, add quantities at each price across buyers.
7Check the option wording for 'ceteris paribus' and extreme words like 'always' before choosing.

Quickest way: Two-question filter for demand MCQs

When to use it: Use in the objective paper when you have under a minute per question.

Ask: did the good's own price change? If yes, the answer is movement along the curve.
If no, ask: which determinant changed, and does it raise or lower buying at every price?
For related goods, use the sign rule: substitute's price up means demand up, complement's price up means demand down.
Eliminate options that pair the wrong cause with the wrong result, such as 'price change causes shift'.
If the question needs a long schedule calculation, do it last. With 0.25 negative marking, skip only when you cannot narrow to two options.

Common mistakes in Meaning and Determinants of Demand

Saying a fall in the good's own price shifts the demand curve to the right.
Students link any rise in buying to an increase in demand.
Fix: Own price change gives movement along the curve (extension or contraction). Only other determinants shift the curve.
Treating all goods as having higher demand when income rises.
Students forget inferior goods.
Fix: Normal goods rise with income. Inferior goods fall as income rises because buyers switch to better goods.
Mixing up substitutes and complements.
Both are called related goods and the signs feel similar.
Fix: Ask if you would use one in place of the other (substitute) or together (complement). Substitute price up raises demand for the other. Complement price up lowers it.
Forgetting the 'other things equal' condition when stating the law of demand.
Students memorise only 'price up, quantity down'.
Fix: Always include ceteris paribus. The law does not hold if income, tastes or expectations change at the same time.
Adding prices instead of quantities when finding market demand.
Students rush through schedule problems.
Fix: At each price, add the quantities of all buyers. Prices stay the same.
Confusing demand with quantity demanded.
The words sound alike.
Fix: Demand is the whole schedule or curve. Quantity demanded is one point on it at a given price.

Worked examples

Example 1

Which of the following will cause a rightward shift of the demand curve for tea, assuming tea is a normal good and coffee is its substitute? (a) Fall in the price of tea (b) Rise in the price of coffee (c) Rise in the price of sugar, a complement (d) Fall in consumers' income

Show the solution

Option (a) is a change in tea's own price. It causes a movement along the curve, not a shift.
Option (b): coffee is a substitute. When its price rises, buyers move to tea, so demand for tea rises at every price. The curve shifts right.
Option (c): sugar is a complement. A higher sugar price lowers tea demand, a leftward shift.
Option (d): tea is normal, so lower income lowers demand, a leftward shift.

Answer: (b) Rise in the price of coffee

Example 2

Two buyers A and B have demand at ₹10 of 4 units and 6 units respectively, and at ₹8 of 7 units and 9 units respectively. What is the market demand at ₹8? (a) 9 units (b) 13 units (c) 16 units (d) 7 units

Show the solution

Market demand at a price is the sum of individual quantities at that price.
At ₹8, A demands 7 units and B demands 9 units.
Total = 7 + 9 = 16 units.
The 13 units option uses the ₹10 row wrongly, since 4 + 9 = 13 mixes prices.

Answer: (c) 16 units

Example 3

The price of a good falls from ₹50 to ₹40 and its quantity demanded rises from 100 to 130 units, with all other factors unchanged. This is best described as: (a) Increase in demand (b) Decrease in demand (c) Extension in quantity demanded (d) Contraction in quantity demanded

Show the solution

Identify the cause: the good's own price fell.
Other determinants are unchanged, so the demand curve does not shift.
Price fell and quantity rose, so the consumer moves down the same curve.
A movement down the curve is called extension (expansion) of quantity demanded.

Answer: (c) Extension in quantity demanded

Exam tips

Questions often test the difference between movement along and shift of the curve. Decide the cause first, then the label.
Learn the sign rules for normal and inferior goods, substitutes and complements. They solve many one-line MCQs.
Watch for options with absolute words like 'always'. The law of demand has exceptions and needs ceteris paribus.
Remember the reasons for the downward slope: income effect, substitution effect and diminishing marginal utility.
In schedule sums, add quantities at the same price and double-check the row you are reading.

Practice questions from Theory of Demand and Supply

Meaning and Determinants of Demand: frequently asked questions

What is the law of demand?

It states that, other things remaining the same, the quantity demanded of a good falls when its price rises and rises when its price falls. It shows an inverse relation between price and quantity demanded. The demand curve therefore slopes downward.

Why does the demand curve slope downward?

Mainly because of the income effect, the substitution effect and diminishing marginal utility. A lower price makes buyers feel richer, makes the good cheaper than substitutes, and attracts buyers who could not afford it earlier.

What is the difference between a demand schedule and a demand curve?

A demand schedule is a table of prices and the quantities demanded at each price. A demand curve is the graph of that table. Both show the same information in different forms.

What are the main determinants of demand?

The main ones are the consumer's income, prices of related goods, tastes and preferences, expectations about future prices and income, and the number of buyers. A change in any of these shifts the demand curve.