The following transcript is an excerpt from “Van Tillian Apologetics, I” by Greg Bahnsen. It can be found for free on iTunes U. The entire series is an excellent resource for those who wish to better understand Presuppositional apologetics as a method.
This particular segment speaks to the reason why the Christian apologist must necessarily reason in a Presuppositional manner:
The apologist must presuppose the truth of God’s word from start to finish in his apologetic witness … When we talk about presupposing or if we talk about a presupposition, what we’re referring to is an elementary assumption in our reasoning in the process by which our opinions are formed – an elementary assumption. And usually in apologetical discussion a presupposition is thought of as at the most basic level of the network of one’s beliefs. Everyone has a set of beliefs that are related to one another, and as it turns out, those beliefs have some sort of structure. There are some beliefs that you’ll give up easier than others; more readily than others. Some beliefs support other beliefs, so that when you give up those beliefs you end up not only giving up the belief in question, but many that relied upon it. So there’s this networking of beliefs that everybody has, and at the most basic level, those beliefs are called our presuppositions. Presuppositions form a wide-ranging foundational perspective or starting point in terms of which everything else we believe is interpreted, in terms of which everything else we believe is evaluated and interrelated. And that’s why presuppositions are said to have the greatest “authority” in one’s thinking. Presuppositions will turn out to be the least negotiable beliefs a person has. People will grant to their presuppositions the highest degree of immunity to revision. So the apologist must presuppose the truth of God’s word from start to finish.
It’s only to be expected that in matters of ultimate commitment the intended conclusion of one’s line of argumentation will also be the presuppositional standard which governs his manner of argumentation for that conclusion. If your conclusion does not dictate your method of reasoning, then it turns out your method of reasoning is not arguing for an ultimate commitment after all. Why not? Because your method has a different basis, or ultimate authority, than your conclusion does.
If somebody says “Dr. Bahnsen, you’re assuming the truth of Christianity when you argue in the way that you do. Your method is dictated by your conclusion”, and I’ll say “well of course, because my conclusion is my ultimate authority. I’m talking about that which is my ultimate way of ‘authorizing’ beliefs.” If somebody says “OK, I want you to use a method that doesn’t assume that – I want you to use a method that has some other authority in mind than your ultimate authority”. I’ll say “now wait a minute. If it’s a method that assumes a different ultimate authority or different authority then what I’m arguing for obviously is not my ultimate authority.”
Let’s go down certain levels here. Why do you believe ‘a’? Well, because of ‘b’. Why do you believe ‘b’? Well, because of a different level ‘c’. Why do you believe ‘c’? You give a different level ‘d’. Now, at some point everybody’s got to get to the bottom. Now for some people maybe its 26 stories, for others maybe its 126 stories. But eventually you get down to the bottom. Now at that point after all of this “why do you believe, why do you believe, why do you believe?” when the person says “Why do you believe that?”, what do you appeal to? Well you have to appeal to your ultimate authority, right? Because it’s ultimate. If it’s not your ultimate authority, if you could answer the question without being circular, you would in fact not be at the ultimate level, because then you would be going down another level.
So the point is – everybody has an ultimate authority. And when that’s what’s in dispute, and that is the case in Christian apologetics – the ultimate authority of the Christian vs. the ultimate authority of the non-Christian worldview – the non-Christian is going to assume his ultimate authority in his method of reasoning, and the Christian is going to assume his ultimate authority in his method of reasoning as well.