When we move along a given demand curve, which of the following changes occurs (holding all other determinants of demand constant)?

• A. Demand increases because consumer preferences shift toward the good (a rightward shift of the demand curve).
• B. Demand increases because consumer income rises (a rightward shift of the demand curve).
• C. Demand decreases because the price of a substitute good falls (a leftward shift of the demand curve).
• D. Quantity demanded changes because the price of the good changes (a movement along the demand curve).

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the difference between a movement along the demand curve and a shift of the demand curve. A movement along the demand curve happens when the price of the good itself changes, holding all other factors constant.
2. Step 2: Recognize that a shift of the demand curve occurs when any determinant of demand other than the good's own price changes, such as consumer preferences, income, or the price of related goods (substitutes or complements).
3. Step 3: Analyze the options given: changes in consumer preferences, income, or the price of substitutes cause the entire demand curve to shift either rightward (increase) or leftward (decrease).
4. Step 4: Identify that when only the price of the good changes, the quantity demanded changes along the same demand curve, which is called a movement along the demand curve, not a shift.
5. Step 5: Conclude that the correct description for a change along a given demand curve, holding other determinants constant, is a change in quantity demanded due to a change in the good's own price.