“For this reason we have spoken of the Christian theistic method as the method of implication into the truth of God. It is reasoning in a spiral fashion rather than in a linear fashion. Accordingly, we have said that we can use the old terms deduction and induction if only we remember that they must be thought of as elements in this one process of implication into the truth of God. If we begin the course of spiral reasoning at any point in the finite universe, as we must because that is the proximate starting point of all reasoning, we can call the method of implication into the truth of God a transcendental method. That is, we must seek to determine what presuppositions are necessary to any object of knowledge in order that it may be intelligible to us. It is not as though we already know some facts and laws to begin with, irrespective of the existence of God, in order then to reason from such a beginning to further conclusions. It is certainly true that if God has any significance for any object of knowledge at all, the relation of God to that object of knowledge must be taken into consideration from the outset. It is this fact that the transcendental method seeks to recognize.”
– Cornelius Van Til, A Survey of Christian Epistemology p.201
We have already indicated that the Christian method uses neither the inductive nor the deductive method as understood by the opponents of Christianity, but that it has elements of both induction and of deduction in it, if these terms are understood in a Christian sense. Now when these two elements are combined, we have what is meant by a truly transcendental argument.
A truly transcendental argument takes any fact of experience which it wishes to investigate, and tries to determine what the presuppositions of such a fact must be, in order to make it what it is. An exclusively deductive argument would take an axiom such as that every cause must have an effect, and reason in a straight line from such an axiom, drawing all manner of conclusions about God and man. A purely inductive argument would begin with any fact and seek in a straight line for a cause of such an effect, and thus perhaps conclude that this universe must have had a cause. Both of these methods have been used, as we shall see, for the defense of Christianity. Yet neither of them could be thoroughly Christian unless they already presupposed God. Any method, as was pointed out above, that does not maintain that not a single fact can be known unless it be that God gives that fact meaning, is an anti-Christian method. On the other hand, if God is recognized as the only and the final explanation of any and every fact, neither the inductive nor the deductive method can any longer be used to the exclusion of the other. That this is the case can best be realized if we keep in mind that the God we contemplate is an absolute God.
– Cornelius Van Til, A Survey of Christian Epistemology p.10-11