A system's wave function is uniquely determined by its underlying physical state

We address the question of whether the quantum-mechanical wave function psi of a system is uniquely determined by any complete description Lambda of the system's physical state. Weshow that this is the case if the latter satisfies a notion of. 'free choice'. This notion requires that certain experimental parameters-those that according to quantum theory can be chosen independently of other variables -retain this property in the presence of Lambda. An implication of this result is that, among all possible descriptions Lambda of a system's state compatible with free choice, the wave function psi is as objective as Lambda.