 The most influential demarcation criterion has been Popper’s original anti-metaphysics barrier: the condition of empirical falsifiability of scientific statements. It required the logically possible relation to basic statements, linked to experience, that can prove general hypotheses to be false with certainty. For this purpose he defended the application of a particular deductive argument, the modus tollens (Popper 1935/1951). Another demarcation criterion is explanatory unity, empirically grounded. Hempel’s deductive-nomological model characterizes the scientific explanation of events as a logical argument that expresses their expectability in terms of their subsumption under an empirically testable generalization. Explanations in the historical sciences too must fit the model if they are to count as scientific. They could then be brought into the fold as bona fide scientific explanations even if they could qualify only as explanation sketches.