 However, Feyerabend also came to think that Popper’s earlier critique of the Copenhagen orthodoxy had been somewhat limited and superficial. According to Popper, the Copenhagen Interpretation was simply the result of some bad positivistic philosophising. Niels Bohr and Werner Heisenberg, on this view, had been seduced by positivist philosophers (like Ernst Mach and his ostensible followers, the Vienna Circle) into thinking that their theory was not conjectural but was merely a compendious, economical but non-hypothetical description of experience. Feyerabend argued that, on the contrary, the Copenhagen theorists had some perfectly good “physical”, “scientific”, or “factual” arguments for thinking that their view alone was currently compatible with the observed results of experiments. He therefore put forward a defence of their instrumentalist interpretation of the quantum theory. But the defence was only tactical, since he ultimately argued that the observed results of experiments themselves needed to be challenged by a point of view which would reveal their truth or falsity. So Feyerabend used the quantum case to push for a reconsideration of the methodological rules to which scientists subscribe. This is the genesis of his idea of a “pluralistic” test model, in which theories are compared with one another, as well as against “experience”. (Note, however, that this idea can already be found in Popper, and that Feyerabend did initially acknowledge this fact). According to Feyerabend, only by endorsing scientific realism can the scientist cleave to a methodology which would consistently bring out the (conceptually) revolutionary potential of scientific theories, rekindling the kind of fire Galileo had lit under the Aristotelian world-view. Such a realism interprets theories not as summaries of experience, but as genuine conjectures about a mind-independent reality. It also puts the observation-language of science in the same epistemological boat as its theoretical terms: observations, he urged, are just as “theoretical” (that is, hypothetical) as theories: “Logically speaking, all terms are ”theoretical“” (Philosophical Papers, Volume 1, p. 32 note).