In demand theory, an increase in demand for a good means which change in the demand curve, holding other factors constant?

Introduction / Context:
Students often confuse an increase in demand with an increase in quantity demanded. This question checks whether you understand the proper graphical meaning of an increase in demand in microeconomics. Examinations use this concept frequently because it is central to demand and supply analysis and to predicting how markets respond to changes in income, tastes, or other determinants beyond price.

Given Data / Assumptions:

• The concept is demand for a good in a standard price quantity graph.
• Other factors such as taste, income, and prices of related goods can change.
• We are asked what an increase in demand means, not what a fall in price means.
• The demand curve is drawn with price on the vertical axis and quantity demanded on the horizontal axis.

Concept / Approach:
An increase in demand means that at every possible price consumers now wish to buy more units than before. Graphically this is represented by a rightward shift of the entire demand curve. In contrast, an increase in quantity demanded means movement along the same demand curve caused only by a fall in the price of the good itself. The key to answering correctly is to separate shift in the curve from movement along the curve and to tie the phrase increase in demand specifically to a shift to the right.

Step-by-Step Solution:
Step 1: Recall that the demand curve shows the relationship between price and quantity demanded, holding other determinants constant.Step 2: When income rises for a normal good or when consumer tastes become more favourable, demand increases at all prices.Step 3: On the graph this appears as a shift of the entire demand curve to the right.Step 4: A movement down the same demand curve happens only when price itself falls, and that is called an increase in quantity demanded, not an increase in demand.Step 5: A shift to the left would represent a decrease in demand, not an increase.Step 6: Therefore, an increase in demand means the entire demand curve shifts to the right.

Verification / Alternative check:
Think of a simple example. Suppose at a price of 10 units of currency, consumers previously wanted to buy 100 units of a good. After income rises, at the same price of 10 they now want 130 units. This is not movement along the old curve but the creation of a new demand curve that lies to the right. At all other prices similar increases in quantity demanded occur. This pattern can only be shown by shifting the curve to the right. The terminology in textbooks consistently uses increase in demand to describe this rightward shift.

Why Other Options Are Wrong:
Movement downward along a demand curve describes how quantity demanded responds to a fall in price, holding other factors fixed, and is not called an increase in demand. A shift to the left is a decrease in demand. A decrease in quantity demanded at each price level is inconsistent with the word increase. A vertical demand curve describes perfectly inelastic demand and is not what the phrase increase in demand means.

Common Pitfalls:
A frequent exam mistake is to treat any increase in the number of units purchased as an increase in demand without asking whether price changed or whether some other factor shifted the curve. To avoid this, always check whether the cause is a change in the good own price or a change in another determinant such as income. Only the latter case should be called an increase or decrease in demand and represented by a shift in the demand curve.

Final Answer:
An increase in demand means that the entire demand curve shifts to the right at every possible price.