Refocusing Bohr's quantum postulate

As recently noted by Landsman, the postulate claimed by Bohr to characterize the essence of quantum theory has not played a major role in modern formulations of the theory. Folse has argued that the postulate nonetheless served a key role in Bohr's development of the “wholeness” and complementarity that underlie standard quantum-mechanical calculations. This paper presents one way to bring the main ideas of the quantum postulate into a sharper focus, one that addresses more directly how quantum mechanics is applied in the analysis of experimental results, and also leads to a useful criterion in evaluating counterfactual assertions about certain kinds of atomic-level measurements.