The law of focuses entirely on the effect of a change in the good's price on the quantity of the good consumed and holds everything else constant.

The law you are referring to is known as the Law of Demand. This fundamental principle in economics states that, all else being equal (ceteris paribus), as the price of a good decreases, the quantity demanded for that good increases, and conversely, as the price increases, the quantity demanded decreases. This inverse relationship between price and quantity demanded can be illustrated through a demand curve, which typically slopes downwards from left to right.

The Law of Demand operates under the assumption that other factors influencing demand—such as consumer preferences, income levels, the prices of substitute goods, and the prices of complementary goods—remain constant. This concept is critical for understanding consumer behavior and market dynamics, as it forms the basis for the downward-sloping demand curves seen in most market analyses.

Understanding the Law of Demand helps businesses and policymakers predict how changes in pricing can affect market behavior, guiding decisions on pricing strategies and economic policies.