This form of Christian apologetics deals with presuppositions.1 A Christian presuppositionalist presupposes God's existence and argues from that perspective to show the validity of Christian theism.2 This position also presupposes the truth of the Christian Scriptures and relies on the validity and power of the gospel to change lives (Rom. 1:16). From the scriptures, we see that the unbeliever is sinful in his mind (Rom. 1:18-32) and unable to understand spiritual things (1 Cor. 2:14). This means that no matter how convincing the evidence or good the logic, an unbeliever cannot come to the faith because his fallen nature will distort how he perceives the truth. The only thing that can ultimately change him is regeneration. To this end, the presuppositionalist seeks to change a person's presuppositions to be in conformity with biblical revelation.
I have found that a person's presuppositions are extremely important when discussing God and the validity of Christianity. I always ask diagnostic questions to find out where a person is philosophically and presuppositionally, so I might better discuss Christianity. This is a very important point to focus on because one's presuppositions will govern how one interprets facts. Please consider the following dialogue as a realistic example of how this works.
Allen: I am an atheist and evolutionist. Prove to me there is a God.
Paul: I do not think I can do that because of your presuppositions.
Allen: Why not?
Paul: Because your presuppositions will not allow you to examine without bias the evidence that I present to you for God's existence.
Allen: That is because there is no evidence for God's existence.
Paul: See? There you go. You just confirmed what I was stating.
Allen: How so?
Paul: Your presupposition is that there is no God; therefore, no matter what I might present to you to show His existence, you must interpret it in a manner consistent with your presupposition: namely, that there is no God. If I were to have a video tape of God coming down from heaven, you'd say it was a special effect. If I had a thousand eye-witnesses saying they saw Him, you'd say it was mass-hysteria. If I had Old Testament prophecies fulfilled in the New Testament, you'd say they were forged, dated incorrectly, or not real prophecies. So, I cannot prove anything to you since your presupposition won't allow it. It is limited.
Allen: It is not limited.
Paul: Yes, it is. Your presupposition cannot allow you to rightly determine God's existence from evidence-- providing that there were factual proofs of His existence. Don't you see? If I DID have incontrovertible proof, your presupposition would force you to interpret the facts consistently with your presupposition; and you would not be able to see the proof.
Allen: I see your point, but I am open to being persuaded if you can.
Paul: Then, I must ask you, what kind of evidence would you accept that would prove God's existence? I must see what your presuppositions are and work either with them or against them.
Presuppositional apologetics differs from Classical apologetics "in that presuppositional apologetics rejects the validity of traditional proofs for the existence of God."3 A pure presuppositionalist tackles the worldview of a person and seeks to change the very foundation of how a person perceives facts.
Adherents to this position have been Cornelius Van Til, Abraham Kuyper, Greg Bahnsen, John Frame, etc.