To simplify let us divide all the determinants of demand in two categories, namely, 'price of commodity itself' in first category and 'factors other than the price' of the commodity, (such as price of related goods, income of consumer and taste of consumer) in the second category.

(i)    Change in quantity demanded. When change (rise or fall) in demand for a commodity is caused by change in its own price, it is called change in quantity demanded. It shows specific quantity of a commodity purchased against its specific price. It is expressed in the form of either extension or contraction of demand. A change in quantity demanded is graphically represented in the form of movement along a given demand curve.

(ii)    Change in demand. When change (rise or fall) in demand is caused by factors other than the own price of the commodity, it is merely called change in demand. It is expressed in the form of either increase or decrease in demand. In fact, change (increase or decrease) in demand is graphically represented by shift of a demand curve upward or downward.

Comparison. 1. Change in 'quantity demanded' is caused by change in price of commodity (i.e., demand curve does not shift) whereas 'change in demand' is caused by factors other than the price i.e., demand curve shifts rightward or leftward.