I just listened to episode 13 of the Fundamentally Flawed podcast which contains a debate between two of the atheist hosts debating two Christian presuppositional apologists including Sye TenBruggencate, the creator of the proofthatgodexists.org website. Mr. TenBruggencate is an adherent of the school of apologetics known as presuppositionalism or reformed epistemology. Basically, the argument goes that the fact that we are capable of knowing anything for certain can only be explained by the existence of an omnipotent and omniscient being who has revealed knowledge to us. Without God as the foundation for all rationality, logic, morality, etc. we have nothing to justify our belief in these things. So long as we admit that we do not know everything, there remains the possibility that what we do not know contradicts what we think we do know. Therefore, the presuppositionalist claims, the only way we can know anything is either if we know everything or if something is revealed to us by a being who does know everything. To any atheist who claims that their knowledge is based on the evidence of their senses, their reason and their memory the apologist will point out that you must appeal to these very things to justify their validity, a circular argument.
Although I've heard a couple debates between atheists and presuppositional apologists, I've yet to hear one where the atheist answers the argument satisfactorily. But it seems clear how to refute the argument. This argument is based on the foundation for absolute knowledge; the presuppositionalist claims that if God did not exist we could not know anything with absolute certainty. He argues that this is an argument in favor of God's existence because in our day-to-day life we all talk and act as if we know at least some things for certain. But I think it is actually a powerful argument against the existence of God because I think it is fairly obvious that nothing can be known with absolute certainty. At this point the apologist would say to me "Are you absolutely certain we can't know anything with absolute certainty?" To which I would respond "No, I am convinced to within a reasonable margin of error to base my behavior on the belief." Such is the nature of all knowledge, absolute certainty is not required nor is it obtained. Yet the apologist would take my admission as his victory, since he has shown that my beliefs are not certainties, while his, he believes, are, he takes this as evidence that his beliefs are truer than mine, but this does not follow. Those who are most certain about the truth of their beliefs are often the mad and fanatical, they are also most likely to be wrong. Certainty of belief is not positively correlated with likelihood of truth. Yet this fact is lost on the presuppositionalist. And his strange insistence on the necessity for certainty in order to claim knowledge is, I think, common among the typical religious believer. There is no end to the arguments the religious throw at the atheist but chief among their objections you will often find a deep-seated emotional aversion to uncertainty. This attitude is also common among the anti-scientific. Science, they complain, keeps changing. Theories are constantly being updated to better account for new data. How, they wonder, can anyone live with a world-view based on such a shifting foundation? It's much more sturdy to stand on a perfect book that has barely changed for 3000 years and is chock-full of certainties and absolutes.
The presuppositional apologists should realize that fervor does not indicate fact, and a little uncertainty can be good for you.