1. In Carl Sagan's so-so novel Contact, an atheist scientist has a conversation with a minister about the relation between faith and science. The scientist character suggests they find themselves a wrecking ball, one of the huge used to demolish buildings. She says they shoud let the ball swing, and that they should each choose where to stand in its path.
The scientist says that she'll used physics to calculate the closest possible safe place to stand. The minister should pray about where to stand.
I was a Christian when I read this story, maybe 12 years ago. I felt a little shock, one that I ignored and shoved away for quite sometime. That shock was the realization that at no point would my faith ever ask me to be in a position where I could be proven wrong.
2. I do not mean to make the old point that faith is unfalsifiable, but it's a related idea.
There are two reasons why we might not know something. The information might just not be available to us, or for some reason, it is impossible for us to understand a given idea.
What did Napolean have for breakfast on June 16, 1785? The information is not available to us, but it could be written down somehere, right? We just don't know where. Let's say this is an incidental limitation on knowledge.
What is it like to be a bat? We can't answer that question - not because the information is not available, but because you must be a bat to experience being a bat. Let's say this is a constitutive limitation on knowledge - no matter how smart we get, we'll never be able to fully answer the question of what it is like to be a bat.
3. I'd like to propose that we can use the distinction between incidental and constitutive limitations on knowledge to make a further distinction between faith and reason.
Incidental limitations are an easy matter for both faith and reason. We will probably always be ignorant about some things, whether Napolean's breakfast on a particular day or whether or not Adam had a belly button.
The difference comes with the constitutive limitations. I think that while both reason and faith have their own versions of constitutive limitations, they react to and handle them differently.
For reason, constitutive limitations are usually seen in one of two ways. They can be reducible to particularily complex incidental limitations - the current debate over brain science is one example of this. Increasingly, people are coming to believe that the mystery of human consciousness actually can be explained in terms of the brain.
Or, constitutive limitations are a matter of hypothetical thought experiments, such as "what is it like to be a bat."
So reason takes constitutive limitations either as challenges to be overcome, or as productive hypotheticals.
Faith, on the other hand, takes constitutive limitations to be fundamental. These limitations are not challenges to be overcome, or interesting hypotheticals, but key points in religious metaphysics and ontology. The will and nature of God, for all that is displayed in revelation, is fundamentally not understandable for humans.
These limitations are mysteries. Even the most hardheaded, apparently rational apologists will eventually admit to believing in mysteries. They will be couched in rational terms, and they will be protected against claims of irrationality, they will be defended to the death, but they are there.
4. Back to the opening story. I think that story hints at a real difference between faith and reason. Reason is inherently risky; it depends wholly upon demonstrations made in public. There is never a point at which one may say "we can't know this" or "we can't question this."
Faith will never ask you to put up or shut up, intellectually speaking. Oh sure, it might ask you to become a martyr, but that has nothing to do with the truth of a faith. Faith is never going to ask you to be in a position where you could be proven wrong on a fundamental basis. No matter how clever or knowledgeable your atheist opponent, you will somehow be able to retreat into mystery.
I am not claim that apologists are pig-headed or stubborn. I am not setting up the atheist version of total depravity, claiming that religious people's hearts are darkened by intellectual sin or something like that. I'm saying this retreat into mystery is a feature, not a bug.