Stu Taba's Rogue Messiah: The Philosophical Wanderer Chapter 3 (Pg. 23-25)

                                                                         Chapter Three
                                       Testing purifies the gold by boiling the scum away
                                                                                                      Jalal Udo-Din Rumi
     The "sufficient evidence" requirement of justified belief leads to the truthseeker's application of scrutiny, which shall be our next focal point. In Chapter Five: The Challenge of Skeptisism, author Tom Morris shows "how the most basic form of skeptical inquiry can give us a fresh perspective on the foundations of all human knowledge." (p. 53)
     Skeptism puts all one "knows" in a new light and "can inspire us with a new and needed humility concerning all our claims to knowledge." Morris first points out that, etymologically, skeptism derives from a Greek word meaning "to inquire." Thus, "skeptisism at its best is not a matter of denial, but of inquiring, seeking, questioning doubt."
     The author next divides all our beliefs into three categories:Past Oriented, Present Oriented, and Future Oriented. Then, the skeptic asks two types of questions: those of source skepticism and radical skepticism. Regarding questions of source skepticism, testimony of others is our main source of  our past beliefs, along with our own first person memory. The skeptic asks how one is to know how reliable onc's memory is.
     There is a logical problem in the answer of past recollection of reliable memory because this reasoning is circular: relying on memory to justify memory is assuming the truth of the thing one is trying to prove. :-[ Regarding testimony as a reliable source for justifying past beliefs, one runs into the same circular reasoning problem when one justifies the reliability of testimony on the testimony of trusted sources (Mom, Dad, etc.). Further, if one reasons that many times in the past, other peoples testimony has proved reliable, "a bigger circle of reasoning is drawn because one is relying on memory  to justify testimony.*L*
     And as regards present beliefs, we base most of them on testimony (of family, friends, and news authorities), which leads to the same circular reasoning problem. :-[  How about sense experience? That is the medium through which we filter our memory and testimony of others. "Perhaps sense experience can give us the direct, provable tie to reality that the skeptic seems to be seeking." But no, the proof of sense experience reliability runs into the very same circular reasoning pitfall!
     One may recall (memory)having seen (sense experience)a penny on the street and upon closer inspection, it had-- in fact--turned out to be a penny. So is your sense experience proved reliable? Well,no, because you first invoked your memory- which cannot be proven reliable- then your memory was of seeing- a sense experience- an object, so once again the logical proof fails. :-[
     Just as our proofs of past and present beliefs fail "that just transfers over to any equal lack of justification for trusting our justification of beliefs about the future." Concludes Morris:
                Notice that the skeptic's questions don't just show that we can't prove the reliability 
                of our sources for belief. The point is much deeper. We can't provide one single,
                pure piece of evidence for this assumption that we all share and on which the
                credibility of our beliefs depends. The sources of our beliefs are sometimes
                reliable. And this fact is certainly perplexing, if not deeply troubling. (p. 61)