“Because of the nature and content of the Christian’s own fundamental presuppositions – involving the authority of God and His revelation – even his conception and method of transcendental argumentation will be a transformed interpretation or understanding which distinguishes his outlook from that of the would-be autonomous man.
Here then is how the presuppositional (transcendental) method of defending the faith would proceed, once the preliminary discussions and clarifications have taken place with the unbeliever – and the two outlooks now come head-to-head. The unbeliever says that he knows that miracles are impossible, that a personal, almighty God does not exist, that ethical principles are not normative across cultural boundaries, etc. Or the unbeliever says that the believer cannot know that the Bible is God’s word, or that Jehovah exists, or that Christ was His Son, etc. The Christian apologist must seek to uncover what this unbeliever’s personal convictions are regarding relevant metaphysical and epistemological matters: e.g., what is the nature of things that are real, how does the world operate, where did it come from, what is man’s place in the world, what is man’s nature, are there moral or epistemological norms that are not chosen by the individual, what are the criteria of truth, what are the proper methods of knowing, is certainty possible, etc.? Once the believer has a fairly good grasp of the general kind of worldview assumed ( or explicitly advocated) by the unbeliever, it should be compared to the worldview of the Christian. The Christian can show that the particular objections raised by the unbeliever, would, within the Christian outlook, not prove to be legitimate objections or intellectual problems at all. Thus, who really “knows” what he is talking about, the Christian or the non-Christian? The cogency of each side’s theory and practice of knowing must be tested within the broader worldviews of which they are part. The apologist explains how rationality, communication, meaning, science, morality, and man’s redemption and renewal are quite understandable, meaningful, coherent, or intelligible within the biblical worldview – within the framework of thinking God’s thoughts after Him. The apologist then subjects the unbeliever’s worldview to an internal critique to show that it is
(1) arbitrary, and/or
(2) inconsistent with itself and/or
(3) lacking the preconditions for the intelligibility of knowledge (language, logic, science, morality, redemption, etc.). Since that is the case, the unbeliever cannot “know” the things he urges against Christianity – indeed, he could not know anything at all and loses all claim to rationality. Thus, the Christian has proved the rationality and necessity of His scripturally based worldview.
The specific questions or philosophical issues with which an apologist chooses to press the unbeliever, and the particular aspects of experience that he selects for application of these issues, are wide, varied, and not prescribed in advance by the transcendental program of proving Christianity and disproving any version of autonomous unbelief. Take anything about which the unbeliever is commited or concerned – anything that seems uncontroversial and agreed upon by the believer and unbeliever alike – and from that point show that it would be unintelligible, meaningless, and incoherent if the unbeliever’s worldview, instead of the believer’s were true. The illustrations are as a wide as human experience – from the curing of polio, to the composing of an opera, to the condemnation of police brutality, to the balancing of your checkbook.”
(Bahnsen, Van Til’s Apologetic, 512-513)