Following a discussion which started here and ended up here, I have had a few more thoughts on the presuppositionalist position. If you are unfamiliar with presuppositionalism I suggest you start here.
I'm going to address three presuppositionalist claims in turn. (Sorry if the following is a bit slapdash but a lot of it has been copied and pasted from my comments at the threads linked to above and is very train-of-thought-ish)
Logic exists. Any attempt to prove the opposite must use logic, thus making logic an axiom.
Same for truth and knowledge. Try and disprove them without using them in the disproof. Impossible!
The concept of God is not an axiom because a potential disproof of God would obviously not rely on the existence of God
So you see I don't need God to account for logic (it is axiomatic), but on the contrary, you need logic to account for God. If you disagree that you need logic to account for God, then this automatically makes your account for God illogical, by virtue of the fact that you are not initially presupposing logic.
2) Christian presuppositionalists have a source of absolute knowledge.
Including, for example, a list of Best Movie awards from the Oscars, and the proof of Fermat's last theorem. If this information isn't in there somewhere, then Scripture does not contain absolute knowledge, meaning the claim of a presuppositionalist that they have a source to such knowledge is wrong.
If a presuppositionalist's response to this is that 'source of absolute knowledge' means just 'God has absolute knowledge', then so what? You just believe in a smart guy. Big deal.
3) Christian presuppositionalists have a basis to expect the uniformity of nature.
Which worldview may reasonably expect that causal connections function uniformly throughout the universe or that the future will be like the past?