“The Reformed method of apologetics seeks to escape this nemesis. It begins frankly ‘from above.’ It would ‘presuppose’ God. But in presupposing God it cannot place itself at any point on a neutral basis with the non-Christian. Before seeking to prove that Christianity is in accord with reason and in accord with fact, it would ask what is meant by ‘reason’ and what is meant by ‘fact.’ It would argue that unless reason and fact are themselves interpreted in terms of God they are unintelligible. If God is not presupposed, reason is a pure abstraction that has no contact with fact, and fact is a pure abstraction that has no contact with reason. Reason and fact cannot be brought into fruitful union with one another except upon the presupposition of the existence of God and his control over the universe.
Since on the Reformed basis there is no area of neutrality between the believer and the unbeliever, the argument between them must be indirect. Christians cannot allow the legitimacy of the assumptions that underlie the non-Christian methodology. But they can place themselves upon the position of those whom they are seeking to win to a belief in Christianity for the sake of the argument. And the non-Christian, though not granting the presuppositions from which the Christian works, can nevertheless place himself upon the position of the Christian for the sake of the argument.”
– Cornelius Van Til, A Christian Theory of Knowledge p.18