Stu Taba's Rogue Messiah:The Philosophical Wanderer Chapter 4 (Pgs. 32-33)

     Author Tom Morris turns next to evidentialism, which holds the principle It is irrational for anyone, anywhere, to believe without sufficient evidence. One can see how self-evidence and sense-evidence are included among. "the allowable possible supports for a rational belief" when the evidentialist principle is broadly interpreted. But immediately one runs into the circular reasoning problem we have already encountered:

                If everything has to have proof or evidence, then what is the evidentialist's
               proof for the truth of the evidentialist principle itself- the principle that makes
               this demand? (p. 71)

Evidentialists may claim their principle to be self-evident, but "many philosopher have denied that it's true at all and they clearly understood it." So it's not true by understanding, or by sense-evidence. And if we nevertheless accept it to be true, we must reject it because it is without sufficient evidence. Thus, the principle is self-defeating. :-[ Yet evidence is important to rational life, so a line must be drawn.
    
     Enter The Principle of Belief Conservation, which is a rational response to skepticism, which allows certain basic beliefs to be rationally held without evidence or proof:

               For any proposition, P: If

                           1. Taking a certain cognitive stance toward P (for example, believing it,
               rejecting it, or withholding judgement) would require rejecting or doubting a
               vast number of your current beliefs,

                           2. You have no independent positive reason to reject or doubt all those
               other beliefs, and

                           3. You have no compelling reason to take up that cognitive stance toward P.

     Morris concludes his introduction to the Principle of Belief Conservation with a fitting metaphor and quotation.

                        Your current beliefs are like a raft or boat on which you are floating, sailing across the seas of life. You need to make repairs and additions during your voyage. But it can never be rational to destroy the boat totally while out on the open sea, hoping somehow to be able to rebuild it from scratch, or else to swim without it.