This claim, however, belies a very shallow understanding of the relationship between faith and reason. Indeed, unless one has faith they have no ground for trusting their reason to lead them to truth.
By the term "faith" is meant "belief or trust despite the lack of proof." We have faith in this sense when we entrust ourselves to the surgeon to perform the operation skillfully and successfully or when we entrust ourselves to the competence of the flight crew when we board a jet.
We tacitly believe the surgeon and the pilot are competent even though we may not have proof that they are.
Modern Neo-Darwinian theory tells us that our reason, like all our cognitive faculties, has evolved to suit us for survival, not for finding truth. It needs be kept in mind that the survival of an individual or a species is only coincidentally related to truth.
If, for example, a belief exists that the more offspring a man has the greater will be his reward in an afterlife, that belief, if it's genetically based, will proliferate throughout the society with every subsequent generation since anyone holding it will doubtless have, on average, more offspring than those who lack the belief.
The belief has wonderful survival value for those who hold it, or at least for their genes, but the belief is false.
Another example: Atheists tell us that religion evolved because it offered comfort and solace and that due to these advantages religion has spread everywhere around the globe. Yet despite the acknowledged survival value of these religious beliefs atheists nevertheless believe them to be false.
In other words, evolutionary success often has nothing to do with truth, so why do we believe that reason has evolved as a reliable guide to truth? The answer is that we have faith that it is.
If it takes faith to believe that reason is trustworthy, what is that faith based upon? Some say it's based on the laws of logic which are independent of human reason, but as Michael Egnor points out in an article at Evolution News, it requires a measure of faith to think that the laws of logic are trustworthy.
Take Descartes' maxim that thinking proves the thinker's existence - "I think therefore I am." It would seem that there's no faith involved in this succinct proof, but as Egnor points out, that's not quite so. He writes:
For example, even Descartes’s assertion, “I think therefore I am,” is not something we can prove without faith. The problem lies in the “therefore.” We must tacitly assume the validity of logic — specifically the logic of non-contradiction — to link “I think” to “I am.”We can't prove the axioms of logic. We accept them on faith. Nor can we prove that reason is trustworthy for to attempt to do so requires us to rely on a rational argument which itself requires us to use our reason. But to use our reason to prove that our reason is reliable is to commit the fallacy of begging the question.
If we do not have faith in logic, then it would be possible to think but not to exist. Of course we find this possibility absurd, but it is only absurd because of our profound faith in the validity of logic — in this case, the validity of the logical principle of non-contradiction. That is the principle inherent in the belief that thinking presupposes the existence of the thinker.
If logic were not reliable, there would be no logical connection between thinking and existence. Thinkers could think without existing.
The secular man and the theist are in the same boat here. Both must exercise faith in the trustworthiness of their reason, but the secular man must have faith that blind impersonal forces serendipitously gave rise to a cognitive faculty that purely by coincidence turns out to be a reliable guide to knowledge.
The theist has faith that his reason is a generally reliable guide to knowledge because she believes it to be the gift of a rational and good God who gives us this cognitive faculty for the express purpose of discovering truth.
I leave it to the reader to decide which option is a priori more reasonable to believe.