" The fundamental mistake made by the philosophical theory of the ultimate sources of our knowledge is that it does not distinguish clearly enough between questions of origin and questions of validity. Admittedly, in the case of historiography, these two questions may sometimes coincide. The question of the validity of a historical assertion may be testable only, or mainly, in the light of the origin of certain sources. But in general the two questions are different; and in general we do not test the validity of an assertion or information by tracing its sources or its origin, but we test it, much more directly, by a critical examination of what has been asserted--of the asserted facts themselves.

Thus the empricist's questions "How do you know? What is the source of your assertion?" are wrongly put. They are not formulated in an inexact or slovenly manner, but they are entirely misconceived: they are questions that beg for an authoritarian answer. "

― Karl Popper , Conjectures and Refutations: The Growth of Scientific Knowledge