Transitivity is Not Necessary to Show That Indifference Curves Cannot Intersect,a Note

Abstract

Professors in intermediate and advanced microeconomic theory courses often propose a proof that indifference curves cannot intersect that relies on the transitivity and monotonicity of preferences. In the interest of stimulating thought on the topic, we derive an elementary proof that indifference curves cannot intersect which relies on fewer assumptions than the traditional proof. We conclude that transitivity is essential in constructing a theory of rational choice; but transitivity is not essential in showing that indifference curves cannot intersect.