Deduction as a construct does not bring forth knowledge any more than induction. Inductivists try to move from what seems plausible, or considered most probably the case, to establishing veracity for a hypothesis. Induction is “open ended” because induction as a process is never fully exhaustive. Rather, it comes to an end once one is satisfied with his personal pursuit. To put it another way, once cognitive satisfaction has been achieved the inductive pursuit is over, but it always stops short of the necessity of the conclusion due to the nature of induction.
The deductive process, on the other hand, can leave people with the impression that deduction brings forth knowledge. This might be true, that deduction yields knowledge, if knowledge were only a matter of construct, which it is not. Indeed, if the deductive process is valid, then the conclusion certainly follows from the premises with necessity. Whether the premises are reliable, however, is another matter that requires further investigation beyond the deduction at hand. Deduction by itself does not bring forth knowledge because for one to know the conclusion he would first require epistemic warrant for belief in the premises that lead to the conclusion, which the immediate deduction at hand does not provide. Of course, that does not imply that deduction cannot aid in obtaining knowledge.
A transcendental argument for God’s existence (TAG) has a distinctly inductive aspect to it because with TAG the Christian investigates what must be true in order for some experience to be possible. Notwithstanding, the manner of the investigation is not “open ended” because the premises of TAG do not merely support the conclusion, they ensure it. Now then, given the aspect of deductive “closure”, whereby the formulation of premises ensures the validity of a conclusion, the conclusion of TAG is not merely a confirmed hypothesis precisely because there is no asserting the consequent with TAG (though there is with all inductive inferences).
Of course TAG is deductive in form, but it is unlike garden variety deductive arguments. What sets TAG apart from common deductions is that with the latter we begin with some truths (or inferences) and reason to others, but that to which we reason is not presupposed as a necessary precondition for the possibility of the original fact of experience.
As Greg Bahnsen often quipped, “The proof of God’s existence is that without Him one could not prove anything.” That is nothing other than “proof presupposes God” (or if proof, then God since God is a necessary precondition for the possibility of proof).
Given the inductive and deductive aspects of TAG, we shouldn’t find it strange that Van Til said that in what he called the “Christian method” of apologetics, we find “elements of both induction and of deduction in it, if these terms are understood in a Christian sense.”
It should be understood that we do not come to know the truth of God through cleverly devised proofs. Nothing could be further from the truth. We know God by nature (through general revelation and conscience), yet we can only justify the knowledge of God by Scripture, the Christian’s ultimate authority. Although our belief in God is justified, the proposition p: “I know God” is not justified apart from Scripture. In other words, we don’t “reason” ourselves to God, but our belief in God is justifiably reasonable.
Apologetically speaking, belief in God is “properly basic” and constitutes knowledge. Belief in God is, also, the most reasonable position to hold if for no other reason, it is unreasonable to argue against God’s existence for to do so one must first presuppose those tools of argumentation that only are possible given God’s existence!
In the end, the precondition of all intelligible experience is the God who is known by nature. Whereas the justification for belief in God as the precondition of intelligible experience is contained only in special revelation. Accordingly, epistemological Externalism gives way to Internalism when not just one’s belief but his knowledge of God (p) is justified.
Philosophical Theology 