Demand: wants are the unlimited desires or wishes people have for goods and services. Other things remaining the same, the higher the price of a good, the smaller is the quantity demanded; and the lower the price of a good, the larger is the quantity demanded. The term demand refers to the entire relationship between the price of the good and quantity demanded of the good. (the demand changes because of other things, but the quantity demand changes because of the price. ) A demand curve shows the relationship between the quantity demanded of a good and its price when all other influences on consumers" planned purchases remain the same. Willingness and ability to pay: a demand curve is also a willingness-and-ability-to-pay curve, the smaller the quantity available, the higher is the price that someone is willing to pay for another unit, willingness to pay measures marginal benefit. When demand decreases, the new demand curve. demand curve shifts leftward .