i) I'm going to take another stab at TAG. It's not my objective in this post to expound Van Til or be faithful to Van Til. If what I say is consistent with his original vision, fine. But this shouldn't be a personality cult.
Likewise, I don't care whether I ended up defending what is technically a transcendental argument, or merely something like a transcendental argument. All I care about is whether there's a good argument to be had–and not the pedigree of the argument.
ii) One preliminary issue is whether TAG is worth salvaging. This has been kicking around for decades. It was controversial at the time. It's still controversial. Not much progress has been made in turning Van Til's programatic claims into a full-blown apologetic.
So we should be open to the possibility that this is a failed idea. It seemed to be promising, but the more it's scrutinized, the less is has going for it. Frankly, there's a certain amount of Reformed chauvinism that's responsible for clinging to this argument no matter what.
That said, I will, in fact, be defending TAG, or a variation thereon.
iii) One difficulty is the interpretation of TAG. In this respect, TAG is like the ontological argument. One of the things that makes the ontological argument difficult to evaluate is attempting to understand what Anselm's claim amounts to. Did he offer one or two different versions of his own argument? What do they mean? You can't even assess the argument unless and until you interpret the argument, although it's possible to give alternative interpretations, then handicap each one.
Of course, Scotus, Descartes, Leibniz, Gödel, Plantinga, and Lowe have all offered their own versions of the ontological argument, so it's possible to bypass Anselm.
iv) A limitation of transcendental argumentation is that this is essentially concerned with epistemology rather than ontology. Here's one definition:
Transcendental arguments are partly non-empirical, often anti-skeptical arguments focusing on necessary enabling conditions either of coherent experience or the possession or employment of some kind of knowledge or cognitive ability, where the opponent is not in a position to question the fact of this experience, knowledge, or cognitive ability, and where the revealed preconditions include what the opponent questions. Such arguments take as a premise some obvious fact about our mental life—such as some aspect of our knowledge, our experience, our beliefs, or our cognitive abilities—and add a claim that some other state of affairs is a necessary condition of the first one. Transcendental arguments most commonly have been deployed against a position denying the knowability of some extra-mental proposition, such as the existence of other minds or a material world. Thus these arguments characteristically center on a claim that, for some extra-mental proposition P, the indisputable truth of some general proposition Q about our mental life requires that P.
I don't think that definition is necessarily a problem for TAG. However, if the pretension of TAG is to present the only adequate argument for God's existence, then this limitation is a serious problem. Surely arguments for God's existence should include metaphysical evidence, and not merely what is needed to ground our mental life. Epistemological arguments shouldn't be the only arguments for God's existence.
v) What is TAG trying to get at? In my view, TAG is not so much a direct or positive argument for God's existence as it is an explication of the consequences which follow from denying God's existence. Depending on the consequences, that, in turn, becomes an indirect argument for God's existence.
Technically, this may not be a transcendental argument, but I'm not a purist.
What have you got to lose by denying God? What's at stake? What's the cost? Once you deny God, what else must you deny? What does that commit you to? After the dust settles, what's left?
The force of TAG depends on how damaging the repercussions are of denying God's existence. After making some minor adjustments, can we leave everything important still intact? Or is the denial of God's existence a universal acid that dissolves everything of consequence?
vi) In that respect, TAG is not one argument, but a family of arguments. Arguments of a kind.
Put another way, TAG is not in itself an argument, but an argumentative strategy. It selects for or develops arguments that share that particular orientation. In that respect, we could regard TAG as a research program.
By the same token, this means there may be some good theistic arguments that don't pertain to that strategy or family of arguments.
vii) If successful, this approach has number of advantages:
a) There are preexisting arguments that dovetail with TAG. Take the "argument from reason" (Lewis/Reppert) or Plantinga's evolutionary argument against naturalism. Take the moral argument for God's existence. And so on and so forth.
Even if these aren't specifically "transcendental," the approach I'm suggesting can point them in that direction. What's there to lose by denying God?
b) Conversely, consistent secular philosophers make damaging concessions.
c) It puts the unbeliever on the defensive.
d) It supplies a unifying principle for a number of otherwise disparate theistic arguments.
viii) But to succeed, it is necessary to develop detailed arguments. For instance, what's the status of abstract objects in a Godless universe?
An unbeliever may say abstract objects are explanatorily necessary, but offer a secular alternative for grounding them. Platonic realism. If so, a Christian philosopher or apologist must show the inadequacy of that alternative.
Or an unbeliever may say abstract objects are explanatorily unnecessary. He may propose secular alternatives which do the same work at a lower metaphysical cost. Fictionalism or structural realism. If so, a Christian philosopher or apologist must show the inadequacy of those alternatives.
And, of course, a Christian must propose a positive model for how God grounds abstract objects.
ix) A casualty of this approach is that TAG ceases to be a silver bullet. It's no longer a snappy comeback to stop the mouth of the unbeliever. For the real work has just begun. Formulating the arguments is painstaking work.
However, the silver bullet was always a blank. The simplicity was illusory. To seriously engage secularism, TAG has to become very sophisticated, to operate at the same level as the best of the secular competition.
x) Finally, whether someone is an evidential or presuppositional apologist can often have less to do with the merits of the respective positions than the aptitude of the apologist. Some people have a knack for sifting historical evidence, but no great philosophical aptitude. Take Kenneth Kitchen or Richard Bauckham. They operate at a very concrete level. Historical particulars.
Others have greater aptitude for abstract reasoning. Take Alvin Plantinga.
Plantinga and Kitchen simply have different skill sets. They couldn't do what they other does even if they tried.
So a certain degree of pluralism in apologetic methodology is to be commended. We need people who excel in different things.