I argue in a non-reductive sense for a plausible epistemic principle, which can (1) theoretically and instrumentally unify or systematize all fallacies, and (2) provide a justification for using such a principle for characterizing an erroneous argument as a fallacy. This plausible epistemic principle involves the idea of an error in the method of justification, which results in a failure to provide relevant evidence to satisfy certain standards of adequate proof. Thus, all fallacies are systematically disguised failures to provide substantive (...) proof: a failure in the attempt to persuade rationally, as opposed to emotionally or rhetorically. I argue that the epistemic idea of begging the question is essential to this idea of a fallacy as an inadequate proof. (shrink)