ABSTRACT
One aim of an interpretation of quantum mechanics is to say which properties are real and which are not. All known interpretations have that goal. According to the pilot wave theory both position and momentum of a particle are real and observerindependent properties, although they cannot simultaneously be known. Modal interpretations, to take another example, purport to identify the real properties of the physical state, which is supposed to be distinct from the quantum state, i.e. the state described by the wave function. In the many worlds interpretation all the different worlds, as described by the quantum state, are real; we just happen to live in one of them, but the collapse is not real. The Copenhagen interpretation claims that the distinction between real and unreal properties depends on preparation conditions: a property is sometimes real, namely when the conditions for its measurement are satisfied, otherwise not. This stance is easily interpreted as a kind of idealism, and that is perhaps one reason why there is a growing discomfort with the Copenhagen interpretation.
