Some critics of reason argue that "faith" should be defined more broadly, and that an element of faith is involved even in the so-called "inductive leap" by which we generalize from a limited set of observations. After all, they contend, we cannot "prove" that we will never encounter a conflicting observation. As will be shown in a later subsection ("Theory and Practice"), however, epistemological certainty does not require that we execute the impossible task of acquiring positive evidence for such a negative claim. Consequently, no "leap of faith" is required by the logical process as it is understood here. The use of the term "faith" in this course is also consistent with common usage, including even the understanding of the term among those who champion faith. The defenders of mysticism, for instance, often extol belief in the absence of evidence—or even in the face of seemingly contradictory evidence—as a virtue.