What is a belief that is accepted by faith alone? Either it's a belief without real reasons behind it or its a belief whose reasons are of a different kind than one that is grounded on reason.
The first hypothesis seems obviously false. In order for someone to believe anything to be true, one must have reasons to do so. Believing that something is true without any reason is a logical impossibility since the effect (belief) would have no cause. Of course, we might argue about the weight of those reasons but we're calling them reasons nonetheless.
So, what about the 2nd hypothesis, can the reasons of a belief grounded on faith be of a different kind than those of a belief grounded on reason? Let's think of some examples and comparisons:
- If Bill believes in God because of some subjective personal experience of His presence, would his belief be based on faith? Not necessarily. It is subjective experience that warrants most of our most basic beliefs and I see no reason why that one in particular should be dismissed as a belief devoid of reason. This could be analogous to the belief in the outside world, we are reasonable in having that belief if there's no stronger reason to deny it. In this case, although Bill would not be able to show God's existence to others, he could still be said to know of God's existence in such a way.
- If Bill believes in God because his parents told him that God exists, then his belief would simply be based on fallacious arguments which doesn't seem to be a fair reason to label his belief as being grounded in faith. His belief is grounded in reasons that may not hold against other contradictory reasons but that's what arguments are for.
- Another case, and probably the most targeted by this distinction, is the case where Bill believes in God because he really wants that belief to be true. You could say that this belief isn't grounded on reason but it would be more accurate to say that this is not a belief at all. Wishful thinking is distinct from belief, one is wanting something to be true, the other is considering it likely to be true so, in this case, Bill doesn't actually believe that God exists, he merely wishes that to be true.
- Then there's the case in the opposite end of the spectrum. The belief in God's existence can come from objective arguments, much in the same way most of our other beliefs originate. Many people in the past, in natural theology, have put forth arguments to support that belief and although we might disagree on the weight of those arguments, the fact is that a belief that forms through such means is surely a belief grounded on reason.