 Viewed as basic physical parts of a hydrogen atom represented by state \(\Psi\), its electron and proton may be considered entangled physical parts since \(\Psi\) cannot be expressed as a product of vectors representing the state of each. The electron and the proton may each be assigned a mixed state, but these do not uniquely determine the state \(\Psi\): state separability is violated. This may occasion no surprise if a system’s state merely specifies its chances of exhibiting various possible properties on measurement. But it may have metaphysical significance if a system’s quantum state plays a role in specifying its categorical properties—its real state, so that the  real state separability principle  is threatened. His commitment to this principle is one reason why Einstein denied that a physical system’s real state is given by its quantum state (though it’s not clear what he thought its real state consisted in). But according to (one variant of) the rival Copenhagen interpretation, the quantum state gives a physical system’s real dynamical state by specifying that it contains just those qualitative intrinsic quantum dynamical properties to which it assigns probability 1. On this last interpretation, violation of state separability in quantum mechanics leads to  physical property holism:  it implies, for example, that a pair of fundamental particles may have the intrinsic property of being spinless even though this is not determined by the intrinsic properties and relations of its component particles.