1.2.3—Ceteris paribus

Ceteris paribus means “other things being equal”: analyse the effect of one change while treating other relevant variables as unchanged.

It isolates a relationship in a model, such as how a price change affects quantity demanded. In the real world, several factors may change at once, so the condition must be stated when applying the result.

“A rise in price reduces quantity demanded, ceteris paribus” holds income, tastes, prices of related goods and expectations constant.

Ceteris paribus does not claim other variables never change; it identifies the controlled comparison used to reason about one effect.