Ceteris Paribus
What is Ceteris Paribus?
Ceteris paribus is a Latin phrase meaning 'all else being equal' or 'holding all else constant'.
Ceteris paribus is an assumption used in economic analysis to isolate the effect of one variable on another while keeping all other variables constant. This allows economists to study cause-and-effect relationships in a complex world. For example, the law of demand states that, ceteris paribus, as the price of a good increases, the quantity demanded decreases.
Ceteris Paribus: a worked example
Take a demand equation for burritos: Qd = 120 - 4P, with P in dollars. At P = 10, Qd = 120 - 40 = 80 burritos. Raise the price to P = 15 and Qd = 120 - 60 = 60. That fall of 20 units is a ceteris paribus result, because only price moved. Now let average income in the town rise, shifting demand out to Qd = 150 - 4P. At P = 15, Qd = 150 - 60 = 90. Compared with the original 80 sold at P = 10, price rose and quantity rose together, which looks like the law of demand failed. Nothing failed. Two variables moved at once, so the 90 sits on a new demand curve rather than the old one, and the comparison across those two points is not a ceteris paribus comparison at all.
The mistake students make with ceteris paribus
Students read ceteris paribus as a claim that other variables actually stay frozen, then announce the law of demand is broken whenever they see a price and a quantity rise together. The phrase feels like a prediction about the world because it sits inside the statement of a law. Ceteris paribus is a bookkeeping rule for the model, not a description of reality. Use it on an exam to decide whether a change moves you along a demand or supply curve or shifts that curve, since only a change in the good's own price produces the movement along.
Ceteris Paribus questions
What does ceteris paribus mean in economics?
Ceteris paribus is Latin for holding all other things constant. Economists attach it to a statement so that a single variable is allowed to move while every other influence is frozen. Saying that a higher price reduces quantity demanded ceteris paribus means the reduction follows provided income, tastes, and the prices of related goods stay put. Without the phrase the claim would be untestable, since any observed change could be blamed on something else in the background.
Why do economists use ceteris paribus instead of studying everything at once?
Economists use ceteris paribus because a market outcome has many causes acting at the same time, and isolating one lets you sign the effect of that cause. If price, income, weather, and input costs all shift together, a rise in sales tells you nothing about which force produced it. Holding the others fixed makes the link between two variables measurable and gives the model a testable prediction, which can later be checked against data that controls for the other influences.
Does ceteris paribus make economic models unrealistic?
Ceteris paribus does simplify, but the simplification is the method rather than a flaw. Physics describes motion without friction first and adds friction back afterward. Economists build the two variable relationship, then reintroduce the other forces as shifts of the curve, so the finished analysis can handle several changes at once. A model turns unrealistic only when someone forgets to put the held constant factors back in before drawing a conclusion about an actual market.
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