 1954 saw the publication of the first of Feyerabend’s many articles on the philosophy of quantum mechanics, the first fruits of the time he spent studying with Popper. In these publications, he generally took the line that the dominance achieved by the “Copenhagen Interpretation” of the quantum theory was undeserved. Feyerabend was particularly keen to argue that it had not and could not be shown that this interpretation of the theory was a general panacea for the problems of microphysics, or that its defenders could justifiably believe it to be unassailable. He came to defend the right of “hidden-variables” theorists such as Louis de Broglie, David Bohm, and Jean-Pierre Vigier to hypothesise the existence of an unobserved deterministic substructure underpinning the apparently indeterministic cavortings of objects on the quantum-mechanical level. 