However, there is one area of apologetics that presents particular difficulty for the non-Christian. This form of apologetics is called Presuppositional apologetics. In this view, the Bible, as divine revelation, is presupposed. There is no "neutral" ground upon which to discuss the existence of a god or the validity of Christianity. The "Transcendental Argument for God" (TAG) is the Presuppositionalist's foundation. As Wikipedia states,
"---a presupposition in this context is a belief that takes precedence over another and therefore serves as a criterion for another. An ultimate presupposition is a belief over which no other takes precedence. For a Christian, the content of Scripture must serve as his ultimate presupposition.... This doctrine is merely the outworking of the lordship of God in the area of human thought. It merely applies the doctrine of scriptural infallibility to the realm of knowing."Presuppositional apologists argue that the assumptions and actions of non-Christians require them to believe certain things about God, man and the world which they claim they do not believe. It is understood that the non-Christian refuses to accept these beliefs and will be condemned to Hell for such.
Beside the fact that this form of apologetics has been refuted (see here and here, for example), it has established itself securely as a legitimate perspective on apologetics. These folks are prominent, active and aggressive.
So, it may be wise when dialoging with an apologist to find out if he/she is of the Presuppositional variety. If so, it is this blogger's opinion that you should just respectfully decline further discussion. There is no way of reasoning with these folks.