 Feyerabend is here referring to Popper’s approach to the epistemology of science, which he himself followed and furthered for quite a while. In chapter II of The Logic of Scientific Discovery (1934), Popper had distinguished between scientific practice and scientific standards, principles, or methodology. Arguing against a “naturalistic” theory of method which makes standards depend on practice, Popper opted instead for a strongly normative epistemology, a discipline which lays down optimum rules of method for scientists to follow. This is one of the most important aspects of the Popperian perspective which Feyerabend originally took on board.