When quantity demanded decreases in response to a change in price , it is called a movement along the demand curve, not a shift of the curve itself.

Core idea

  • The law of demand says that, ceteris paribus, when the price of a good rises, the quantity demanded falls; when the price falls, the quantity demanded rises.
  • A decrease in quantity demanded “in response to a change in price” means the price has gone up, so buyers move to a point with a lower quantity on the same demand curve.

Movement vs shift

  • Decrease in quantity demanded :
    • Caused only by a change in the good’s own price.
    • Shown as a movement up and to the left along a fixed demand curve.
  • Decrease in demand :
    • Caused by factors like income, tastes, prices of related goods, expectations, or population.
    • Shown as a leftward shift of the whole demand curve.

Typical exam-style completion

If the question is:

“When quantity demanded decreases in response to a change in ______”

the standard completion is:

“…a change in price , there is a movement along the demand curve (a decrease in quantity demanded, not a decrease in demand).”

TL;DR: When quantity demanded decreases in response to a change in price, buyers move along the existing demand curve because the price has risen.