Popper's Falsificationism and the Demarcation Problem

Karl Popper set out his mature philosophy of science in Logik der Forschung (1934, translated into English in 1959 as The Logic of Scientific Discovery), written in Vienna while Popper stood in close but critical dialogue with the Vienna Circle without ever joining it. Popper rejected the logical positivists' verification principle as both philosophically confused, since it rendered universal scientific laws strictly unverifiable, and as the wrong tool for the job it was meant to do: distinguishing genuine empirical science from non-science or pseudoscience, a problem Popper called the demarcation problem. His alternative criterion, falsifiability (or refutability), holds that a theory counts as scientific only if it is logically capable of being contradicted by some possible observation — that is, only if the theory forbids certain observable states of affairs, so that its falsity could in principle be established by empirical test, even though its truth can never be conclusively established by any finite number of confirming instances.