Action Specifically Implies the Contrary of Indifference

Indifference can never be demonstrated by action. Quite the contrary. Every action necessarily signifies a choice, and every choice signifies a definite preference. Action specifically implies the contrary of indifference. The indifference-concept is a particularly unfortunate example of the psychologizing error. Indifference-classes are assumed to exist somewhere underlying and apart from action. This assumption is particularly exhibited in those discussions that try to "map" indifference curves empirically by the use of elaborate questionnaires.

The concept of "indifference" may be important for psychology, but not for economics. In psychology, we are interested in finding out intensities of value, possible indifference, etc. In economics, however, we are only interested in values revealed through choices. It is immaterial to economics whether a man chooses alternative A to alternative B because he strongly prefers A, or because he tossed a coin. The fact of ranking is what matters for economics, not the reasons for the individual's arriving at that rank.

--Murray N. Rothbard, "Toward a Reconstruction of Utility and Welfare Economics," in On Freedom and Free Enterprise: Essays in Honor of Ludwig von Mises, ed. Mary Sennholz (1956; repr., Auburn, AL: Ludwig von Mises Institute, 2008), 237.