Resumen: In this paper I examine the problem of circularity in the justification of knowledge from the point of view of argumentation theory. I introduce the expression founding argument for the arguments we use to try to prove that we know, and explain the classical account of the two fallacies that may be committed: ad ignorantiam and petitio principii. A new definition of both fallacies, based on recent work in the theory of argumentation, is used to show that not every founding argument is fallacious.
Palabras clave: argumentation, argument circularity, begging the question, epistemic justification