Why all reason is faithful (even if not all faith is reasonable)

I want to pick up here where my post "When is a belief rational?" left off. There I argued (following A. Kenny) that reason is found in a proper balance between credulity (willingness to believe) and skepticism (unwillingness to believe).

Interestingly, this definition has important consequences for the way we view the faith/reason relationship. Today many people accept a dichotomy between the two. Sadly, Mark Twain's smarmy definition of faith as "believing what you know ain't true" is often taken seriously, leading to derogatory epithets toward those deemed to have faith as being "faith heads" (Dawkins' preferred term).

It cannot be said too strongly that this conception of faith is a canard, that is an utterly spurious conception. If willingness to believe is written into the very conception of reason, then the rational person is the one who exercises the proper amount of faith, not the one who eschews faith. And this means that the atheist who insists he exercises reason, but not faith, is like the child who insists he breathes air, but not oxygen.

Let's consider a quick example. These days those who tend to reject faith typically are enamored of science. One of the cornerstones of science is observation, and the cornerstone of observation is human sense perception. So how do we know that sense perception is reliable?

Philosophers have long attempted a non-circular way to defend the reliability of sense perception (that is, a demonstration that does not depend already on the reliability of sense perception). But there are only two avenues that one might accomplish such a proof: a priori (that is, pure rational reflection) and a posteriori or empirical (that is, depending on sense perception). All attempts at the former have failed woefully, and the latter obviously assume what needs to be proved. (For more see William Alston, The Reliability of Sense Perception.)

The result is that we must trust our sense perception. We must have faith in our experience of the world. This is striking indeed, for it means that our fundamental engagement with the world all the way from an infant grapling with colored blocks to a nuclear physicist studying the latest test results, is predicated on faith.

"But sir, I really don't breathe oxygen! Indeed, I can't stand the stuff!"

Yeah, right.