The Gospel Coalition is running a series on methods in apologetics. The latest installment is “Questioning Presuppositionalism” by Dr. Paul Copan, who raises four criticisms of presuppositionalism, one of which is the old canard that presuppositionalists engage in fallacious circular reasoning. (I think all four are misguided in one way or another, but the other three will have to wait for now.) He writes:
First, it engages in question-begging — assuming what one wants to prove. It begins with the assumption that God exists, and then concludes that God exists. Such reasoning would get you an “F” in any logic class worthy of the name!
Dr. Copan is a gentleman and a scholar, so I’m sure he doesn’t realize quite how insulting this sounds to presuppositionalists! (For comparison, imagine someone claiming that evidentialists commit the fallacy of affirming the consequent because they use inductive inferences.) This criticism has been answered many times, so it’s disappointing to find it cropping up yet again (although perhaps presuppositionalists should take comfort from the fact that Dr. Copan doesn’t offer any new criticisms!). Even so, I’ll try to explain one more time why this complaint so badly misses the mark.
In his contributions to the book Four Views on Apologetics, Dr. Copan’s fellow apologist William Lane Craig notes that this is a common criticism of presuppositionalism:
As commonly understood, presuppositionalism is guilty of a logical howler: it commits the informal fallacy of petitio principii, or begging the question, for it advocates presupposing the truth of Christian theism in order to prove Christian theism.1
However, Craig also recognizes that the criticism is fairly superficial:
If this were all presuppositionalism had to offer as an apologetic, it would be so ludicrous than no one would have taken it seriously. But at the heart of presuppositionalism lies an argument, often not clearly understood or articulated, which is very powerful. This is an epistemological transcendental argument.2
Dr. Copan is also well aware of presuppositionalism’s use of transcendental argumentation, as his TGC article illustrates:
Typically, these presuppositionalists (e.g., Bahnsen) avoid traditional cosmological (causal), teleological (design), and moral arguments, but they enthusiastically endorse the transcendental argument for God (TAG) — the argument to show that God is the inevitable ground for all rational thought.
It’s therefore all the more surprising to find him repeating the “begging the question” charge, for once one understands the nature of a transcendental argument it’s clear that no fallacy of petitio principii is being advocated or committed. A transcendental argument typically takes the following form:
(1) If X were not the case, Y would not be possible.
(2) Y is possible.
(3) Therefore, X is the case.
In the presuppositionalist’s argument, X is the existence of God and Y is rational thought. (For simplicity, I’m using Dr. Copan’s own terminology here; I’m also glossing over some technical questions about the formalization of TAG, some of which were addressed in my exchange with David Reiter, but none of them affect my argument here.) So let’s assume that the following is a workable summary of TAG:
(1) If God did not exist, rational thought would not be possible.
(2) Rational thought is possible.
(3) Therefore, God exists.
One common criticism of TAG is that presuppositionalists haven’t adequately defended the first premise. However, that’s not Dr. Copan’s criticism. His charge is that presuppositionalism is guilty of “assuming what one wants to prove.” But how exactly does the argument above assume what it sets out to prove? How does it assume the existence of God in any rationally objectionable fashion?
The problem here is that Dr. Copan, like many critics of presuppositionalism (and even some of its would-be defenders), confuses a presupposition of an argument with a premise of an argument. There’s a significant sense in which the argument above does indeed presuppose the existence of God. For if the first premise is true, the existence of God is a necessary precondition of rational thought, and the possibility of rational thought is a presupposition of all argumentation, including TAG. So in an obvious sense, if TAG is sound then TAG presupposes the existence of God (and so does the cosmological argument, the teleological argument, the moral argument, and every other theistic argument). But this is not at all to imply that the existence of God functions as a premise in the argument. TAG doesn’t look remotely like this:
(P1) God exists.
(C) Therefore, God exists.
Nor does TAG employ any premises that trivially presuppose the existence of God (e.g., “God is all-knowing” or “God has spoken in the Bible”). So it’s hard to see exactly why Dr. Copan thinks that presuppositionalism flunks Logic 101.
Perhaps the following analogy will help to set the record straight. Descartes’ famous argument — “I think, therefore I am” — can be seen as a kind of transcendental argument; specifically, a transcendental argument for one’s own existence. I cannot doubt my own existence without thinking, but I can think only if I exist; thus even my doubting presupposes my existence. I can doubt my own existence only on pain of performative inconsistency: the content of my intellectual act (the denial of my existence) is inconsistent with the performance of my intellectual act (the doubting of my existence).
So, does Descartes’ Cogito beg the question? Does it simply assume what it purports to prove? Does it commit a logical howler? Not at all. It’s far more subtle than its crude parodies (e.g., “I stink, therefore I am”!). As I mentioned above, the argument identifies a performative inconsistency in the one who doubts his own existence. (In a sense, all transcendental arguments aim to identify a performative inconsistency in the skeptic’s position.) Does it presuppose its conclusion? Yes, in the sense that the argument can be mentally entertained by a person only if that person exists — but that’s precisely the point. This sort of non-trivial ‘presupposing’ is necessarily involved in all transcendental arguments that purport to identify a necessary precondition of rational thought.
Once you see that Descartes’ argument doesn’t beg the question in any objectionable fashion, it ought to be clear that neither does the presuppositionalist’s argument. For whereas René Descartes argued, in effect, that his existence is a necessary precondition of his intellectual activity, Cornelius Van Til argued that God’s existence is a necessary precondition of his intellectual activity (and of everyone else’s). As someone once quipped, whereas Descartes argued, “I think, therefore I am,” Van Til argued something far more profound: “I think, therefore I AM.” (If you don’t get it, review Exodus 3:14!)
Whatever other criticisms it might invite, Descartes’ anti-skeptical argument would not have garnered the attention it has if it transparently committed the fallacy of petitio principii. Yet the presuppositionalist’s argument can be seen as very similar in its logical form. It simply isn’t true that presuppositionalism commits an elementary logical blunder — and it’s high time its critics laid that tired old charge to rest.