How Bohr Specifically Adapted William James’s “Complementarity” for Physics Many Years After Bohr First Read James’s “Complementarity”: Setting the Historical Record Straight in Order That James’s Complementarity Can Be Properly Evaluated on Its Own Merits for Quantum Measurement
Authors: Snyder Douglas Michael 
Published: February 2024

Today it is important to see James’s original complementarity in 1890 independently of Bohr’s discussions on complementarity in order that James’s conception can be properly evaluated as the model on its own merits for quantum measurement. On the basis of new evidence and a deeper analysis of previous evidence presented here, it is very reasonable to conclude based on Bohr’s own words that Bohr read James’s complementarity between approximately 1908 and 1912. An Appendix provides the relevant text from both Bohr’s Nobel biography and his interview with the American Institute of Physics to support this conclusion. Bohr’s description of significant events in his life are matched with dates in his Nobel biography, adding support to the conclusion. How Bohr specifically adapted James’s complementarity to physics is presented. Bohr’s discussion of “mental activity” is compared here to James’s definition of complementarity focusing on consciousness and is found to be extremely similar to James’s definition. In addition, a side by side comparison of James’s definition of complementarity and Bohr’s most important and well-known definition of complementarity for physics is presented. This comparison shows just how Bohr adapted James’s complementarity to Bohr’s complementarity for physics. Examining the chapters “The Stream of Thought”” (chapter 9 in James’s “The Principles of Psychology”) and “The Relation of Minds to Other Things” (chapter 8 in “The Principles of Psychology”) shows that the very evidence that James used to develop complementarity in “The Relation of Minds to Other Things” is discussed in “The Stream of Thought,” a chapter that Bohr acknowledged reading and concerning which he had a very high opinion. It is also made clear in the paper that Bohr was aware that he had a choice to adopt complementarity for physics along the lines of James’s complementarity, which he had read, and that he rejected this possibility. Instead, in his complementarity for physics, Bohr adopted a very different approach fundamentally based on the necessity of a physical interaction between a physical system and a physical measuring apparatus with an uncontrolled aspect to obtain a specific measurement result. Bohr attempted to apply the uncertainty principle to this uncontrolled feature of the physical interaction. Bohr’s approach has been the widely adopted framework for understanding quantum measurement since 1927. The historical description of complementarity in Bohr’s Nobel biography is discussed in light of the evidence presented and is shown to be incorrect. It is important to set the record straight regarding the origin of complementarity so that James’s complementarity is not seen as an appendage of Bohr’s version of complementarity for physics. Bohr’s attempt to extrapolate what his Nobel biography incorrectly states was complementarity originally developed by Bohr, which was for physics, to other fields confuses and detracts from the importance of James’s complementarity which was in fact the original. Bohr’s detour with his proposed necessity (and its proposed fundamental significance) of a physical interaction in the measuring process with an uncontrolled aspect in quantum mechanics has distracted attention away from the possible significance of James’s original concept in psychology to quantum measurement, including its evaluation on its own merits as to whether it provides the correct conceptual framework for this measurement.