Back to the original question: why should falsifiability be the criterion? It is not that falsification directly leads to the rejection of a theory. That would be a rule of the bucket view of science. It is not that we must always look for theories that are more falsifiable. That would also be a rule of the bucket view of science. Popper's main methodological rule is that scientists must try to guess and corroborate (or equivalently falsify) bold and useful conjectures and take any falsification as a problem that can be used to start a critical discussion. In other words, the usefulness of falsifiability is that falsifiable conjectures say more, because they prohibit more and, in the case of their falsification, they lead to useful problems, which steer the creative process of science. For Popper, who knew most of section , this is exactly what we should expect from a scientific theory.