 This sufficient condition for an “element of reality” is often referred to as the EPR  Criterion of Reality.  By way of illustration EPR point to those quantities for which the quantum state of the system is an eigenstate. It follows from the Criterion that at least these quantities have a definite value; namely, the associated eigenvalue, since in an eigenstate the corresponding eigenvalue has probability one, which we can determine (predict with certainty) without disturbing the system. In fact, moving from eigenstate to eigenvalue to fix a definite value is the only use of the Criterion in EPR.