A presuppositional apologetic is a distinctly Reformed or Calvinistic approach to the defense of the Christian faith. Unlike classical apologetics it holds that there is no "neutral ground" between the believer and unbeliever, there is not a pile of worldview facts that we agree upon at all. To give you a picture say you meet Mr.Unbeliever and he says "Why yes I believe in God, but I don't think we need to believe in Jesus to be saved." Now a classical approach would come alongside Mr.Unbeliever and say: "Well now this is great, we already have so much in common, let me give you some reasons why you should add Jesus to you belief system that is already there."
So basically the classical apologetic sees this person who claims to believe in God but not Christ as being a good deal "right" he or she merely needs to add belief in Jesus to what is already there. Now a presuppositional approach sees this is all wrong, for the simple fact that the presuppositionalist sees the Bible and Christ alone as the revelation of God to man. Also the presuppositionalist sees all truth as God's truth and to deny this God is to cut yourself off from the foundation of truth. With that said the presuppositionalist sees that there are NO NEUTRAL FACTS. All facts are either interpreted through a regenerate eyes or fallen eyes.
With all of that said let us come back to Mr. Unbeliever this time he meets a presuppositionalist, their encounter is a bit different from the one he had with the classical evidentialist, it goes something like this:
Mr unbeliever "So yes I do believe in god but I don' believe I need Jesus."
Presup: "What do you mean by "god"?"
Unb: "god (little g in the presuppositional view) I see as more of a force that is in everything, no need for a saviour because we are all part of god."
The presuppositionalist will say, "Actually the god you are talking about is an idol and you are suppressing the truth in unrighteousness. And if we do assume your worldview that god is only an impersonal force then you have no foundation for ethics, laws of logic, human rationality, human dignity...yet you believe in these things and in doing so really are borrowing from the Christian worldview."
The difference between the evidentialist and the presuppositionalist is tremendous. In the one case the unbelievers fallen idol of "god" is merely absorbed in the other it is toppled over. (Now to be fair to the evidentialists this isn't the best picture but it is just that a picture) Unbelief from the presuppositional perspective is challenged at every corner, even to the point where as Van Til states that when a Christian and an unbeliever both look at a rose they don't see the same thing. The one sees a creation testifying to the glory and majesty of God the other sees a pretty red flower. I agree.
What I like most about presuppositionalism is that it meets the challenges against Christianity head on. Rather then dealing with every bullet the unbeliever fires in challenge of the Christian faith, it slaps the gun out of the unbelievers hands by showing that if you reject the Christian revelation you can not consistently make the challenges (bullets) you are making.
One of my favorites is the charge that "Science has disproved God." (Some Atheist actually has a book out now with that in it's title, I believe it is on the NY Times bestseller list. The worst books usually are.) At anyrate the problem with such a preposterous charge is that really without God there is no foundation for science. Science proceeds upon the assumption that the future laws of nature will be like the past laws of nature, this is fine in the Christian worldview because God upholds and provides the regularities we see in nature.
Without the Christian foundation science's foundation is upon a leap into non-reason. There is no reason apart from God to believe the future will be like the past but we need to assume that in order for the scientific method to proceed at all so we just make an irrational leap (and borrow from the Christian worldview).
This is what Schaeffer called "taking the roof off" basically you are for the sake of argument assuming the unbeliever's presuppositions and showing where they lead. In the above case we assumed like many scientists that there is no God, well when you do that the scientific method is based upon an irrational leap.
So What About Evidences?
This brings me to the actual point of this post. Given the presuppositional method what role do evidences actually play? Now in Riddleberger's lectures on Schaeffer he pointed out that Schaeffer really combined a presuppositional Van Tillian approach with and evidentialist approach. I honestly think there is wisdom here on Schaeffer's part.
One of the things Schaeffer was adamant about in his work at L'abri was that there is no question that is off limits, because if Christianity is the truth it can answer all objections. What Riddleberger pointed out is that at some point you need to answer people's questions, you can't just keep pointing out how without a Christian base their very questions are irrational. That is true I think, however when people ask why we believe certain things like the resurrection we should be able to give sensible answers.
This does not mean we need to compromise sola scriptura and say after long arguments Christianity is probably true like the evidentialist. However, we should be able to give reasons for what we believe and answer people's questions. This will require some degree of evidences.
I think the difference and what we want to avoid is how the classical and Arminian approaches use evidences, the only conclusion that can be reached in that method of apologetics is not one of certainty that demands the unbeliever to submit or keep rebelling to the truth. All that can be said in the classical approach is that Christianity after looking at the evidences is "probably" true.
That seems a tad dishonoring to the Triune God. To lean on a Van Tillian illustration, I wouldn't dare say to my wife when she asked if I loved her "I probably do." How much more when we are giving a defense of the faith given to us by God Almighty.
That said what I am at the moment trying to work out is a synthesis of presuppositionalism and evidences to answer people's questions. This seems rather sensible to me. To sum up: the type of evidentialism I would reject is the kind that takes neutral ground with the unbeliever and gives evidences in a vacuum. This is where the believer stops being a believer for the sake of argument and says things like "ok IF God exists...Let's pretend God exists...God is the most likely explanation for X" etc.
Apologetics can't be done in a vacuum like that, chiefly for the reason that I don't think it is honoring to God. Not only that it compromises sola scriptura. On the flip side a presuppositional Reformed approach doesn't do apologetics in a vacuum but on the basis of the God who is there and His revelation to man, these are the presuppositions without which all reasoning becomes self contradictory and relativisitic. However, I don't know if that is all we should say. I am inclined to think that the use of evidences is perfectly sound within the framework of the presuppositions we already have.
In other words, we can use evidences as a tool in answering questions, however we must be clear that they are not the foundation the house of Christian theism rests upon, they are more or less aesthetics that are there to attract the unbeliever. Well that is where I am right now on this, I hope it was understandable and helpful to my presuppositionalist freinds.