 In the letter to Schrödinger of June 19, Einstein points to a simple argument for the dilemma which, like the argument from the 1927 Solvay Conference, involves only the measurement of a single variable. Consider an interaction between the Albert and Niels systems that establishes a strict correlation between their positions. (We need not worry about momentum, or any other quantity.) Consider the evolved wave function for the total (Albert+Niels) system when the two systems are far apart. Now assume a principle of locality-separability (Einstein calls it a Trennungsprinzip—separation principle): Whether a determinate physical situation holds for Niels’ system (e.g., that a quantity has a particular value) does not depend on what measurements (if any) are made locally on Albert’s system. If we measure the position of Albert’s system, the strict correlation of positions implies that Niels’ system has a certain position. By locality-separability it follows that Niels’ system must already have had that position just before the measurement on Albert’s system. At that time, however, Niels’ system alone does not have a state function. There is only a state function for the combined system and that total state function does not single out an existing position for Niels’ system (i.e., it is not a product one of whose factors is an eigenstate for the position of Niels’ system). Thus the description of Niels’ system afforded by the quantum state function is incomplete. A complete description would say (definitely yes) if a quantity of Niels’ system had a certain value. (Notice that this argument does not even depend on the reduction of the total state function for the combined system.) In this formulation of the argument it is clear that locality-separability conflicts with  the eigenvalue-eigenstate link,  which holds that a quantity of a system has a value if and only if the state of the system is an eigenstate (or a proper mixture of eigenstates) of that quantity with that value as eigenvalue. The “only if” part of the link would need to be weakened in order to interpret quantum state functions as complete descriptions. (See the entry on  Modal Interpretations  and see Gilton 2016 for a history of the eigenvalue-eigenstate link.)