 Harrigan and Spekkens (2010) have introduced a framework for discussing these issues. In their terminology, a complete specification of the physical properties is given by the ontic state of a system. An ontological model posits a space of ontic states and associates, with any preparation procedure, a probability distribution over ontic states. A model is said to be \(\psi\)-ontic if the ontic state uniquely determines the quantum state; that is, if there is a function from ontic states to quantum states (this includes both cases in which the quantum state also completely determines the physical state, and cases, such as hidden-variables theories, in which the quantum state does not completely determine the physical state). In their terminology, models that are not \(\psi\)-ontic are called \(\psi\)-epistemic. If a model is not \(\psi\)-ontic, this means that it is possible for some ontic states to be the result of two or more preparations that lead to different assignments of pure quantum states; that is, the same ontic state may be compatible with distinct quantum states.