Note that all influences on consumption of a good other than its own price are assumed constant in deriving the law of demand.

The Latin term ceteris paribus refers to the idea that "all other influences" on some dependent variable are held constant while examining the effect of changing a single independent variable.

Thus, the law of demand deals with the independent influence of price on the quantity demanded (the dependent variable), ceteris paribus. Much of economic analysis follows the lead of the great economist Alfred Marshall in using this "all else assumed equal" technique so that we can examine, one at a time, the variables that affect human behavior. Indeed, this "controlled experiment" approach is used throughout science to gain insights into how the world works.