Presuppositions of Van Til's TAG

I recently interacted at Pyromaniacs over an interesting post on presuppositionalism (link) to test a theory. In short, I was attempting to figure out whether the transcendental argument for the Christian God’s existence utilized by Van Til (link), Sye Bruggencate (link), and other “Van Tilian” apologists eventually requires an appeal to a self-authenticating divine revelation in order to be sound. Surprisingly, the two people who replied to me ended up agreeing with this. And this is not the first time this has happened (see posts 13, 15, and 16 here). Perhaps if the comment section wasn’t closed so quickly – and unfortunately, as I never got a chance to reply to one of the last posters who dismissively accused me of being a Unitarian and God-rejector while making elementary false dichotomies – there would have been others who would have stepped forward in agreement. The best thing to do in such situations occur is to shrug your shoulders and move on. And so, I’m going to reproduce what I consider to be the more relevant points I made from a few of the comments I left (refer to the first link for the full context):

I'm merely asking you to defend your proof. For it to be a proof, the Christian God must be the conclusion of an argument. The argument, or so I understand, is that because God is the precondition of proof (premise 1), and because proof is necessary (premise 2), God exists (conclusion). But a conclusion is only as true as its premises. I’m questioning how you came to know premise 1. 

This is, in rough form, the TAG I have in mind throughout this post.

The OP provides a practical argument for accepting first principles in general, but insofar as it intends to parallel the goal of Van Til, Sye, etc. - viz. to prove the Christian worldview in particular - I never understood why an atheist just couldn't respond: “Okay, so what is unique about your God (“the floor”) such that He (“it”) is the precondition for intelligibility, and why is this property necessary?” After all, in order to function as a “proof” for Christianity in particular, there must be something that distinguishes Christianity from infinitely many non-Christian worldviews.

The point of this comment is simple: to get the user of the TAG to identify what it is about the Christian God which makes him the precondition for proof or knowledge, and to understand why such a unique property is epistemologically necessary. Otherwise, an aforementioned premise 1 of the TAG is undercut, and the TAG itself will fail.

…a burden of proof is on you as well. For you are defending an alleged proof for [the Christian] God. It is not enough to just state that God alone is the very precondition for proof. That’s well and good, but that is, as it stands, itself an assertion in search of an argument. 

This is designed to explain why the user of the TAG is obligated to defend his premises. As I said in an above comment, as a proof, the conclusion of the TAG is only a good as its premises. If the premises are attacked, they need to be defended. Of course, as the user of the TAG will be presupposing God throughout his replies, it is to be expected that his defense will presuppose God as well. But an ontological presupposition is not necessarily an epistemological presupposition. The TAG clearly states that God is ontologically necessary for proof; the point is to find out if the TAG must also claim God (or, more precisely, God’s revelation) is an epistemological necessity as well. That is, it is just because God exists that proofs can allegedly be proffered - but will the substantiation of this eventually presuppose Scripture?

Now, if your answer to my question about premise 1 outlined above is just a deduction from Scripture, then I will ask you to prove Scripture. Eventually, you will hopefully see that something - God’s word, in fact - must be taken for granted without proof for the simple reason that we are not omniscient. Something must be self-authenticating, and whatever proposition[s] is or are taken as first principle[s] will be one’s alleged sufficient condition for knowledge. 

Now, both of the individuals I spoke to agreed that this is the case. And this would seem to be a point for Scripturalism, although on further reflection, I suppose there would still be some question as to whether Scripture itself has something to say about the hypothetical legitimacy of a separate, divinely sanctioned source of knowledge. In any case, though I could be wrong, I suspect the above agreement would be atypical if presented to most others who use “Van Til’s TAG.”

For example, take a popular proponent of this argument - Sye Bruggencate, who was mentioned in the post itself. I recently had the misfortune of witnessing Sye Bruggencate attempt to refute Scripturalism. Honestly, for a man whose apologetic method emphasizes logical argumentation, you would not expect to see Clark’s view so quickly dismissed with simplistic and common canards such as that empirical knowledge is necessary in order to even understand the Bible, let alone far-fetched objections like that one needs infallibilistic knowledge in order to obey a given command.

Then too I was initially presented with an argument in the comment section that the doctrine of the Trinity could function as a necessary and uniquely Christian tenet. But I argued that this line of reasoning too must, in the end, resort to Scripture:

Why one and three? Why not one and two or one and four? What about the personality of said God? Can all of His or their attributes really be deduced via reductio ad absurdems alone? 

And:

Again, for emphasis, the Trinity would be *an* explanation of unity and diversity, not necessarily the *only* explanation... unless we resort to a self-authenticating divine revelation.

And:

This is a good point too. By your own admission, then, belief in the Christian doctrine of the Trinity is only a necessary condition for belief in Christianity. That is, there are non-Christians who believe the Trinity. But that means the Trinity isn't a sufficiently unique doctrine.

To summarize, apart from Scripture, there does not appear to be any reason to prefer Trinitarianism to Binitarianism, a Quaternity, etc. And further, if non-Christians can believe in the doctrine of the Trinity, as my correspondent smartly pointed out, then the doctrine of the Trinity turns out to be not so uniquely Christian after all. Something more would be needed to explain why such people are inconsistent. What, if not Scripture? On the other hand, if Scripture, then:

I see no need to appeal to Trinitarianism at all as an intermediary step if we can and must appeal to Scripture anyway. Scripture itself is the unique doctrine of Christianity which contains the set of propositions which by definition distinguish the God whose word it is from all else.

That is, Van Til’s TAG - TAGs in general actually - serve an important purpose, but they are not the crux of Christian apologetics. They specify necessary but ultimately insufficient conditions for knowledge. Indeed, how we even know they are necessary is conditioned on what our sufficient condition[s] for knowledge has or have to say about them. To conclude with a reply I made to a friend who had a question about the initial comment I left:

The floor analogy is good if it is meant to depict our need for first principles in general. We all [must] operate on one or more presuppositions. The alternative - for us - is infinitism, and that leads to a never-ending justificatory process, which is why it is self-defeating. So far, so good. 

And yet, this argument for first principles is itself only a necessary condition for knowledge. It isn’t a sufficient condition. For example, the idea that first principles are necessary doesn’t specify a theory of language, logic, or metaphysics. It doesn’t provide us with the means by which we come to know truth. But I argue these are also necessary for knowledge - infallibilistic knowledge, anyway. In short, this [true] argument about the need for first principles is mutually dependent with other necessary truths. 

We aren’t omniscient. We will never be omniscient. So we have to take something for granted, and whatever this is cannot be proved. Rather, it will have to be self-authenticating. This isn’t a problem, because the idea “all propositions require proof” is suspect to the reply that this assertion itself needs to be proved. In my case, God’s word is my first principle, and I view it as a and the sufficient condition for knowledge - to emphasize, it is sufficient, not merely necessary, although it does account for subsidiary necessary conditions like the ones mentioned above. But if God’s word is self-authenticating, it cannot be “proved” per se.  

We can invoke its self-attestation and internal evidences - such as its ability to account for the necessary conditions for knowledge I mentioned above - for it, and these are excellent apologetic tools, but the idea that something is self-authenticating is antithetical to the idea it can be proved. There is nothing, for instance, which could be used to demonstrate that Philemon is canonical other than that it is God’s word. How do we know it is canonical? Well, because it is. There is no higher authority or epistemic criterion by which we can judge it to be God’s word. 

Again, this isn’t a problem, but it’s also not a proof. For it to be a proof, it would have to be a conclusion of an argument. But the only way that Philemon could be proved as God’s word would be if there were one system of truth about which we had comprehensive knowledge. We would need to be omniscient to know the truths of Philemon are necessary truths, because there is no simple reductio ad absurdem we can construct against one who rejects it as God’s word unlike, say, reductio ad absurdems we can construct against those who deny logic or first principles (as Frank did in his post).