This chapter introduces in more comprehensive fashion than elsewhere in the literature the interesting role of Heisenberg in the EPR debate. Although we have already published an analysis of Heisenberg’s posthumously published draft response to EPR, only now are we able to situate this excellent primary source in its fullest context, by contributing a chapter describing, for example, Heisenberg’s thinking prior to EPR about interacting systems and hidden variables, the crucial role of Grete Hermann for Heisenberg’s thinking about separability, completeness and observational context, and describing the correspondence between Heisenberg and Bohr discussing Heisenberg’s manuscript.

This is a translation of the excerpts published in Naturwissenschaften of Grete Hermann’s 1935 essay on philosophy of quantum mechanics, recently translated into English. Her main thesis, in line with her natural-philosophical training and neo-Kantian commitments, is to argue that quantum mechanics does not refute the principle of causality. Quantum mechanics cannot be completed by, hidden variables, because it is already causally complete (albeit retroductively). In establishing this provocative thesis, she makes important use of Bohr’s principles of correspondence and complementarity and of Weizsäcker's version of the gamma-ray microscope, arguing that the lesson of quantum mechanics is the impossibility of an absolute description of nature independent of the context of observation.