The fear of the Lord is the beginning of wisdom, and knowledge of the Holy One is insight.Proverbs 9:10
Presuppositional apologetics is essentially an approach to giving a reason for the hope we have (1 Peter 3:15) that places Scripture in the sole position of authority. We view this approach as the most biblically sound method as well as the most effective in challenging the attacks of the unregenerate.
These sorts of discussions ultimately break down to fundamental differences in worldview. In order to even have a worldview, one must make certain assumptions, or presuppositions. The classical and evidentialist apologetic methods allow the unbeliever to select their assumptions without challenge and then use them to critique Scripture and their Creator. The presuppositional approach attacks those assumptions directly and shows that the worldview they wish to promote does not actually support those ideas. It then goes on to show that the only worldview that allows the assumptions the unbeliever wants to make is the very worldview they hate – biblical Christianity.
To make this more clear, let’s tackle some specific examples: logic, and morality.
The unbeliever typically holds to a materialist/naturalist/athiest worldview – and holds “science” in a high regard. Of course, their actual understanding of science is typically poor and more propaganda-based than concept mastery, but we can set that aside for now. This worldview rejects the spiritual – i.e. immaterial – and holds that everything is atoms and science can answer everything needed. This is of course easily rebutted – see our Kalam argument for details.
The issue for them is this: where do you find logic in an immaterial world? They want to use logic as if it allows them to describe objective Truth about reality, and thus allows them to reason about it. The immaterial worldview does not permit logic to exist in the way that they use it. The only “logic” available to the materialist is nothing more than opinion – and therefore, it cannot be used to prove anything to be true. When they attempt to argue with the Christian using logic – this is a presupposition that must be challenged. They cannot simply say “I have to assume it” or “it just is that way” because that allows them to paper over the fact that they are using it without justifying how it can possibly exist in their worldview. It cannot be justified by the materialist – in fact, it can only be justified as a reflection of the perfect mind and intellect of the Lord. Therefore, do not permit them to use logic to slander and mock Him – because they cannot.
Their arguments for moral positions fail in almost exactly the same way. When the materialist asserts something is wrong or evil, the reply of the Christian must simply be “By what standard?” Calling something bad implies there is something good that is being measured against. What standard of good are they referring to? In the materialist worldview, there isn’t one. They will be forced to admit this when pressed, and will have to defend moral relativism. Of course, moral relativism by definition states there are no absolute right and wrong moral positions, and so the materialist saying so is again merely an opinion, and not a standard that holds any force outside of their own mind.
This is a huge subject and the serious Christian should invest the time to learn it. The works of Cornelius Van Til and Greg Bahnsen are foundational. For a very solid and enjoyable introduction, watch Sye Ten Bruggencate’s movie “How To Answer The Fool” here on YouTube. You can find his website here.