High Quality Content by WIKIPEDIA articles! In 1947, John von Neumann and Oskar Morgenstern exhibited four relatively modest axioms of "rationality" such that any agent satisfying the axioms has a utility function. That is, they proved that an agent is (VNM-)rational if and only if there exists a real-valued function u defined on possible outcomes such that every preference of the agent is characterized by maximizing the expected value of u, which can then be defined as the agent`s VNM-utility (it is unique up to adding a constant and multiplying by a positive scalar). No claim is made that the agent has a "conscious desire" to maximize u, only that u exists.