Karl Popper’s logical and epistemological insights are the basis of a widely used methodology for judging the success of scientific theories – or more accurately, of scientific “research programs,” defined as the evolving set of theories that share a common set of assumptions (or “paradigm” in the language of Thomas Kuhn). Imre Lakatos’s Methodology of Scientific Research Programs judges an evolving theory in terms of how it responds to falsifying instances – via ad hoc adjustments (bad) or via content-increasing hypotheses (good) – and how well it predicts facts in advance of their discovery. A theory that evolves in content-increasing ways, and that predicts novel facts in advance of their confirmation, is called “progressive”; a theory that fails to do so is called “degenerating.” Particularly important are predictions that differ from those of a competing theory – which in the case of MOND is the standard cosmological model.

Scientific epistemology begins from the idea that the truth of a universal statement, such as a scientific law, can never be conclusively proved. No matter how successful a hypothesis has been in the past, it can always turn out to make incorrect predictions when applied in a new situation. Karl Popper argued that the most important experimental results are those that falsify a theory, and he proposed falsifiability as a criterion for distinguishing science from pseudoscience. Popper argued in addition that scientists should respond to falsifications in a particular way: not by ad hoc adjustments of their theories, but in a way that expands the theory’s explanatory content. Popper argued that the success of a modified theory should be judged in terms of its success at making new predictions. Popper’s view of epistemology, which is shared by many scientists and philosophers of science, is called “critical rationalism.” An epistemology that judges success purely in terms of a theory’s success at explaining known facts is called “verificationism.” Popper argued that verificationism is equivalent to a belief in induction, and that induction is a fallacy.