Dr. Casey said, “If I understand what you say about Bahnsen’s work, David, there would appear to be no possibility of a discussion between a believer and an unbeliever.”
This is often the first impression that people get when hearing about Van Til’s apologetic method, but it is not what he argued. Van Til argued that the very possibility of discussion between believer and unbeliever is due to the fact that they are both made in the image of God. He called this the “point of contact.” So, Van Til’s method was to argue transcendentally, showing that the unbeliever cannot make sense of reality without the Christian God. To argue transcendentally (as Van Til used it) is to say that something is a necessary precondition of something else.
So, a transcendental argument for the existence of God (TAG) would say that God is the necessary precondition for X. One example of a TAG could be formulated as follows:
(1) If God does not exist, then (universal, immaterial, invariant) laws of logic do not exist.
(2) Laws of logic do exist.
(3) “God does not exist” is false.
(4) Therefore, God exists.
Van Til and Bahnsen would then spend ample time in defending premise (1). However, they would also note that there is not one TAG but many possibilities of formulations for TAG’s. Others commonly used involve induction, science, and morality.
Also, many accuse Van Til of endorsing viciously circular reasoning/argumentation. Here is a link to where a follower of Van Til answers that and other objections:
Hope this is helpful.