 In his early work Feyerabend (1962) appealed to historical cases to reject Hempel’s account of explanation and Nagel’s parallel account of intertheoretic reduction (traditionally postulated mechanisms of cumulative progress), on the ground that in actual historical practice meaning change occurs from one major theory to its successor. Deducibility thus fails. It also more obviously fails because the two theories are typically mutually inconsistent. Accordingly, one cannot reason by traditional logical argument from one to the other. Feyerabend introduced his own conception of incommensurability into this work. Anticipating his later broad pluralism, early Feyerabend also extended the Popperian line on testing to a full-blown proliferationist methodology. Competing theories should be multiplied and tested against each other, because more empirical content is thereby brought to light than in testing theories in isolation. In his later work, Feyerabend (1975, 1987, 1989) moved vehemently away from the positions of the Popper school. He vigorously rejected the idea of a scientific method that makes science superior to other cultural enterprises. According to his “methodological anarchism”, any so-called methodological rule, including logical consistency, could be fruitfully violated in some contexts. That said, his well-known slogan, “Anything goes”, was widely read as more radical than he intended, given his playful interactions with his friend Lakatos.