As 2010 draws to a close, it seems hard to believe that it has been 25 years since Greg Bahnsen’s presuppositional apologetic first laid waste to atheistic philosophy in his debate with Gordon Stein. It was in that debate that Bahnsen referred to Van Til’s presuppositional approach as the "Transcendental Argument for God" or TAG. The short sloganized version of the argument is Van Til’s statement that the Christian God exists because of the impossibility of the contrary.
Since that time there has been plenty written about TAG – a lot of it more noise and confusion based on a total misapprehension of the issues involved in the argument. To understate it, TAG is misunderstood by many. In fact, a lot of the noise surrounding TAG has come from Christian apologists of the so-called “classical” and "evidentialist" schools of apologetics. The most frequent of these charges is that TAG is circular. As well, this is a charge that occasionally comes from the man-in-the-street as a first-blush objection.
To dispel the mistaken charge of circularity, we should note first that historically Bahnsen’s debate opponents, Gordon Stein and Michael Martin, never made such a charge. Stein, for one, realized he had no answer to TAG and after the debate stated that he was working on a rebuttal; Stein never published a rebuttal. If the rebuttal were that TAG was circular, it is rather remarkable that an educated and intelligent man such as Stein never produced it. Then there is the professional philosopher, Michael Martin. Martin has not charged TAG with circularity. If it were, Martin, too, would have had no problem producing the proof of circularity.
An oft-quoted aphorism states that imitation is the sincerest form of flattery. Martin, in fact, attempted to mimic TAG with his failed TANG (Transcendental Argument for the Non-existence of God). TANG, though not properly transcendental, attempted to be – and, as such, is a testament that Martin clearly understood the issues involved in TAG and recognized TAG’s power. But TANG, as Martin stated it, is intended to be a “counterexample” to TAG that thereby “logically” establishes that TAG is unsound. Therein lies the rub. Providing a supposed counterexample is not a transcendental refutation and is rather simply a restatement of an opposing worldview. To construct a transcendental argument, we must ask what are the contents of a worldview, and are they coherent, intelligible and not self-contradictory or self-refuting? In short, do they withstand the transcendental critique of being internally consistent (non-self contradictory) and non-arbitrary. Indeed Martin's worldview contents do not! In fact the pluralistic godless world of Martin's TANG describes an impossible world which, in turn, proves God's existence!
In Martin’s case, his worldview is atheistic pluralism which he posits as the “necessary preconditions” for the non-existence of God. Of course, if God does not exist, he has no properties whatsoever (or whatever properties Martin wants God to have so that he would not exist under the postulates of his atheistic pluralism). The co-ultimate components of Martin’s pluralistic universe are nature, logic and morality. The God Martin describes in TANG is like one who awoke after an eternal nap and discovered himself surrounded by nature, logic and morality. In other words, physics, logic and morality are all ultimate and God is not. Such a God is not the God of Christian theism. The God of Christian theism is the ultimate being – and He is as He has revealed himself. To construct a counterexample based on a being who is not ultimate is simply a straw man, a logical fallacy, and misrepresents Bahnsen's point. So much for TANG being a counterexample to TAG and invalidating TAG!
So in the end, we have that TAG is not circular in the trivial manner that is charged – and this from the examples of atheists of repute among atheists.
What still remains then is the challenge of TAG to unbelievers, such as Martin, who merely posit the existence of one or more of the eternal uniformity of nature, morality, and abstract realities such as logic and mathematics. This is an incoherent mix of eternal impersonal ultimate things with no essential relation to each other. (And this does not include the additional challenge against the metaphysical irrationalism of the atheistic interpretation of quantum mechanics which calls into question any ultimate uniformity of the physical universe.) Martin's incoherent mixture multiplies unrelated particulars and compounds unexplained irrational mysteries (for example, what is the source or basis of interactions between, physics, logic, and moral laws?). On top of all this are the internal contradictions that spring from this mixture of "co-ultimates."
Since Martin is unable to provide an intelligible account of his absolutely independent and non-interacting eternal brute facts, he is unable to argue against Christianity on any ground whatsoever – whether it be morality, science, or logic.
For one example, Martin wants to appeal to “abstract logic” in TANG. But logic is a formalization of laws of thought -- that is of valid deduction -- and as such, logic presupposes a mind, and then a thinking being. To postulate eternal mindless laws of thought is an absurdity. But Martin doesn’t tell us where, when or how a mind came into being, whether there was always a mind (an eternal personal mind is something that is too close to theism for him, no doubt) or that it was born from matter-in-motion.
If Martin appeals to reality as just eternal matter and that the laws of physics are just expressions of the inherent properties of matter, one should see that the laws of logic are not inherent properties of matter. And if minds sprang out of matter, they are not free, and rather are always subject to the laws of physics – laws of thought nowhere enter the picture.
Without human free agency, one cannot provide an account of how matter obeying physical laws can generate actions that appear to conform to laws of logic, such as modus ponens, as just one example. If someone would violate a law of logic in an argument and reach a false conclusion (compelled by physics, of course) it would be ridiculous to say the laws of physics were in error. But such is one of the many contradictions of atheism. Atheism is still transcendentally refuted by TAG.