The method of reasoning by presupposition may be said to be indirect rather than direct. The issue between believers and non-believers in Christian theism cannot be settled by a direct appeal to “facts” or “laws” whose nature and significance is already agreed upon by both parties to the debate. The question is rather as to what is the final reference-point required to make the “facts” and “laws” intelligible. The question is as to what the “facts” and “laws” really are. Are they what the non-Christian methodology assumes that they are? Are they what the Christian theistic methodology presupposes they are?
The answer to this question cannot be finally settled by any direct discussion of “facts.” It must, in the last analysis, be settled indirectly. The Christian apologist must place himself upon the position of his opponent, assuming the correctness of his method merely for argument’s sake, in order to show him that on such a position the “facts” are not facts and the “laws” are not laws. He must also ask the non-Christian to place himself upon the Christian position for argument’s sake in order that he may be shown that only upon such a basis do “facts” and “laws” appear intelligible.
– Cornelius Van Til, The Defense of the Faith p.122-123