[The Reformed method] 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.
– Cornelius Van Til, A Christian Theory of Knowledge p.18