A set of assumptions that characterize rational preferences. The standard axioms are completeness (given any two options x and y then either x is at least as good as y or y is at least as good as x), transitivity (if x is at least as good as y and y is at least as good as z, then x is at least as good as z), and reflexivity (x is at least as good as x). Preferences that satisfy these axioms can be represented by a set of indifference curves that do not cross. This represents the starting point for the standard theory of choice.