I had an interesting discussion with a coworker the other day. He claimed his main reason for being non-religious was that he had no sense of "faith." he didn't trust anything that he couldn't see, touch, smell, taste, or hear. In other words, he was a pure empiricist: the whole of reality, he claimed, can be tested and experienced and proven. None else can be rightly called "truth."
Furthermore, he seemed to hold a thinly veiled disdain for anyone whose epistemological tendencies differed from his. It seemed he thought that whoever believed in something they couldn't prove was full of it.
"And don't get started on that wind bulls--t," he warned. "Everyone always brings up the wind. 'How do you prove the wind exists? You can't see it.' But that's stupid. I can feel the wind." And he's right, of course. I told him I agreed: the wind is probably a bad example to illustrate the meaning of faith. The wind can be experienced in a very real and tangible and measurable way. It's empirical.
But what about tomorrow? I asked him. Can you prove that tomorrow will happen?
"No, you can't," he admitted.
Well, then, do you believe that tomorrow will happen?
This is where he hesitated. Of course he believes tomorrow will happen. To say "no" (as he eventually--stubbornly--did) would be a lie: why come to work, if you felt no expectation to receive the paycheck? Why purchase anything with that paycheck, if you don't expect it to benefit your future? In short, why sow without expecting to reap? All of life's activity indicates a sort of faith that there will indeed be a thing called "tomorrow," even though we cannot prove it will happen.
Now of course you can counterargue with something like this: "mathematically, given there is a 1, there must be a 2; and given there is a 2, there must be a 3; and so on. Therefore, given that there was a yesterday and a today, the existence of tomorrow is a mathematical necessity."
But that doesn't really solve the practical problem of all. Even if tomorrow's nonexistence is a mathematical impossibility, you still have no reason to believe you will be around to see it. And yet you live as if you certainly will be. You make investments, you make friends, you make promises - all based on faith that if/when tomorrow comes, you will be there.
"Well," you can argue even more, "that's not blind faith. That is faith based on solid empirical evidence - namely, the decades I've been alive. I am not assuming I'll live tomorrow based on nothing; I'm assuming it based on the fact that, countless of other times, that's how it's happened in the past."
Ah yes, but who told you the future will resemble the past? We all make this assumption, but as philosopher Bertrand Russell pointed out, we have no way of knowing it to be true. It is based on circular logic: we assume the future will resemble the past, because it always has in the past. Is that really sufficient reason?
How do you know the sun will rise tomorrow morning? "It always has," you could say, but then you run into the problem just described. Alternately, you could appeal to the laws of spatial motion, but then I'd have to ask you: "how do you know those laws will still hold true tomorrow?" You would have to shrug and say, "they always have." And, we've run into the same problem as before, only in a more roundabout way.
Now, I certainly don't want to say that belief in such unprovable things is a bad thing. Quite the contrary: it's important that we believe the sun will rise, that tomorrow will happen. Those beliefs are extremely helpful. But let's always remember that they're based on an unfounded philosophical assumption ("the future will resemble the past"), just like religion is based on an unfounded philosophical assumption ("there is a God"). So if one wishes to attack religious behavior by claiming it isn't based on valid assumptions, they would have to attack most of human behavior by the same principle.
In short, we all act on faith. All 6.8 billion of us on this little planet. It is how we live. The only difference between us is what we choose to place our faith in.
A footnote: I am tempted to bring up the plethora of persons whose cases were studied by William James in his legendary book, "The Varieties of Religious Experience." James calls their supernatural encounters "quasi-sensible," but still very real. Some day, we'll discuss the exact nature of such experiences in more depth. But that is a topic for another day.