I tend to follow Rene Descartes' skepticism. If you've even heard of Descartes, you're probably familiar with his famous "Cogito, ergo sum," usually translated as "I think, therefore I am." There was very little Descartes felt we could know with certainty, since all of our sensory experience could be an illusion, but he could infer from the mere fact that he was questioning that, at the very least, the questioner must exist.
I've come up with a similar proof of something Descartes took for granted: the capacity to be mistaken. The proof goes something like this:
Premise 1: Anyone who believes something to be true that is in fact false is fallible.
Premise 2: I believe I am fallible.
I am either fallible or infallible.
If I am fallible, then my belief in Premise 2 is correct.
If I am infallible, then by believing myself to be fallible I believe something false, and am therefore by Premise 1 fallible.
I therefore must be fallible.
(Of course, this only proves my fallibility if Premise 2 is true. If you happen to believe you are infallible, well, you are probably mistaken about that, but this proof cannot prove it to you.)
Now, this seems like a trivial and obvious thing to prove. Of course I can be mistaken. Why would I even entertain the possibility that I might not be? Most of us, if we think about it at all, take our fallibility for granted and then promptly forget about it, adopting beliefs with unwarranted confidence at the drop of a hat. But we sometimes forget that absolutely any idea or thought we entertain, regardless of its original source, remains subject to our own fallibility.
I mention this because it comes up a lot in the religious context, particularly with the fundamentalist crowd. Fundamentalists and scriptural literalists seem to feel that their own fallibility doesn't need to apply, since it's not their ideas but the literal text of the Bible, the very Word of God, which is the belief in question. In a way, it's an attempt to abrogate cognitive responsibility: "Hey, don't blame me! It's God's truth, not mine! I'm just following orders!" Yet there really is no way to escape the fact that whatever you believe, even if it happens to be true, is written on the flawed paper of your own brain; your knowledge and beliefs are tainted with your fallibility; it's only as reliable as you are.
This is one of the objections I raise when people try to convert me to their fundamentalist religion. They ask me to accept a set of propositions with a level of certainty that my fallible human brain simply cannot support: I can be wrong, and the thing about being wrong is it feels exactly like being right. I don't care how strongly, how intensely, how confidently I may believe something; the magnitude of my fervour has little bearing on my likelihood of being correct. And so, indelibly tainted with this doubt in my ability to know something with certainty, I simply cannot embrace a set of beliefs which promise to make everything make sense if only I believe them.
Now, there's an interesting argument that came up in some of these comment threads. If God is truly omnipotent, could He not imbue me with certainty about some truth or other? Well, an omnipotent God by definition could do that, I suppose. And being fallible, of course, I'm in no position to state with complete confidence that I could never be certain of any divinely revealed knowledge. Maybe I could. But it seems to me evident that whatever such a God could do, He hasn't. I remain uncertain about pretty much everything. And more, since I grasp this notion of fallibility and how being wrong feels subjectively just like being right, there seems to be no way for a True Believer to convince me that his knowledge of God's reality is somehow privileged and Really, Truly, Knowledge, and not just another of the countless mistaken beliefs we humans flock to. Sure, they feel like you know, but why should I trust the magnitude of their fervour, when I don't even trust my own?
They tell me, just believe and I'll see. Okay, I believe that much is true; if I believe the way they do, well, yeah, I'll believe the way they do. Big deal. But then both of us might be believing something false, and they can offer no assurance against that, other than simply reaffirming that I'll "know" (read: strongly believe) we're both right.
As far as I can tell, the problem is logically insurmountable. And sure, God might have the power to help me overcome it, I'll grant that. But so might Flying Spaghetti Monster. Indeed, any belief that God or FSM or my Lucky Astrology Mood Watch can give certain knowledge can have the same effect. In short, all I have to do to overcome the proof of my fallibility is to deny Premise 2: stop believing I am fallible.
That's really what they're asking me to do, when you get right down to it. Buy into a belief that asserts my own infallibility with respect to some privileged set of beliefs, to assert that I cannot be wrong about such things. And I'm just not prepared to do that. Oddly enough, I feel it would be terribly impious of me; God (if He exists) gets to know things with certainty, but that's not for us to pretend to.