The discussion between the two positions must therefore be one that takes place for the sake of the argument. This means that each takes his place, hypothetically only, upon the pre-supposition of the other in order to see what happens to human experience.
Since the Christian must seek to win the non-Christian, it is he who should first be ready to think himself sympathetically into the position of the party he is trying to win. He therefore listens patiently to all the objections that the non-Christian has against the Christian position. But he at once sees that all these objections rest upon one fundamental assumption, the assumption of man’s ultimacy. And therefore the real question between the two positions has not even been touched unless it be asked upon what foundation the non-Christian can make his objections to Christianity intelligible. On what foundation rest the guns which he directs against the Christian position?
When this question is considered, it appears that this placement is the truth of Christianity itself. In other words, the non-Christian needs the truth of the Christian religion in order to attack it. As a child needs to sit on the lap of its father in order to slap the father’s face, so the unbeliever, as a creature, needs God the Creator and providential controller of the universe in order to oppose this God. Without this God, the place on which he stands does not exist. He cannot stand in a vacuum.
– Cornelius Van Til, The Dilemma of Education p.40-41