A quick qualm…
I’ve noticed a slew of presuppositional apologists on the Internet basing the entirety of their apologetic around the issue of certainty in knowledge.
That has its place. Richard Pratt does something similar here – http://www.amazon.com/Every-Thought-Captive-Defense-Christian/dp/0875523528/ref=sr_1_2?ie=UTF8&qid=1337572150&sr=8-2
But not all knowledge claims are claims to certainty.
And not all knowledge is certain.
Enough about certainty itself though; that is not the subject of this post.
Rather, when the apologist is engaged with an unbeliever it needs to be pointed out not merely that the unbeliever cannot know anything for certain, but that the unbeliever cannot know anything at all. This is a much stronger point.
I will throw in the qualification that the claim of the aforementioned statement is the case if the unbeliever were consistent in his or her beliefs and practices. No unbeliever is consistent.