own price. Then we let the product’s price vary and study how its change
affects quantity demanded. We can do the same for each of the other
variables in turn, and in this way we can come to understand the
importance of each variable.
Holding all other variables constant is often described by the expressions
“other things being equal,” “other things given,” or the equivalent Latin
phrase, ceteris paribus. When economists speak of the influence of the
price of gasoline on the quantity of gasoline demanded, ceteris paribus
they refer to what a change in the price of gasoline would do to the
quantity of gasoline demanded if all other variables that influence the
demand for gasoline did not change.