Graphically, how is the market demand curve for a product obtained from individual consumers' demand curves?

Introduction / Context:
In microeconomics, demand analysis begins with the demand curve of an individual consumer, which shows the relationship between the price of a good and the quantity that person is willing and able to buy. To move from individual behaviour to the entire market, economists need to combine individual demand curves into a single market demand curve. This question asks how this aggregation is done graphically.

Given Data / Assumptions:

• We have multiple individual demand curves for the same product.
• The market demand curve represents total quantity demanded at each possible price.
• Options mention greater than the sum, horizontal sum, vertical sum or a curve that is steeper than any individual demand curve.
• The axes are standard: price on the vertical axis and quantity on the horizontal axis.
• We assume all consumers face the same market price.

Concept / Approach:
The market demand curve is obtained by summing the quantities demanded by all individual consumers at each price level. Graphically, this is done by adding quantities horizontally because the horizontal axis measures quantity. For every price on the vertical axis, we read the quantity demanded from each person's demand curve and add those quantities to get the market quantity demanded. Therefore, the market demand curve is the horizontal sum of the individual demand curves, not a vertical sum and not some curve that is simply steeper or greater than the sum.

Step-by-Step Solution:
Step 1: Consider a particular price level on the vertical axis. Step 2: For that price, read the quantity demanded by each individual consumer from their demand curve. Step 3: Add these quantities together to obtain the total quantity demanded in the market at that price. Step 4: Plot this total quantity on the horizontal axis at the given price. Step 5: Repeat this process for many price levels and connect the resulting points to form the market demand curve, which is the horizontal sum of the individual curves.

Verification / Alternative check:
Think of a simple example with two consumers. At a price of 10 units of currency, consumer 1 demands 3 units and consumer 2 demands 2 units. The market demand at that price is 5 units. At a price of 8, they may demand 4 and 3 units respectively, giving a market demand of 7 units. When plotting these combinations, we are always adding quantities along the horizontal axis while keeping price fixed. This confirms that the process is horizontal summation. Vertical summation would incorrectly add prices at the same quantity level, which is a procedure used for public goods, not for ordinary private goods in a standard market.

Why Other Options Are Wrong:
Greater than the sum of the individual demand curves: The market demand curve exactly reflects the sum of individual demands at each price; it is not greater than this sum. Steeper than any individual demand curve: The relative steepness depends on how individual demands change with price and is not a general rule derived from aggregation. The vertical sum of individual demand curves: Vertical summation is used in special cases like public goods where the quantity is fixed and willingness to pay is added, not in ordinary market demand. Any blank option: Not relevant because the correct description is given explicitly among the options.

Common Pitfalls:
A common misunderstanding is to assume that because price is on the vertical axis, we should add prices rather than quantities when moving from individual to market demand. Another pitfall is confusing the aggregation of demand with the aggregation of willingness to pay for public goods, where vertical summation does apply. Keeping in mind that the market demand curve answers the question how much is demanded at each price makes it clear that we must add quantities horizontally, not prices.

Final Answer:
Graphically, the market demand curve is obtained as the horizontal sum of individual demand curves.