By this rejection of God, agnosticism has embraced complete relativism. Yet this relativism must furnish a basis for the rejection of the absolute. Accordingly, the standard of self-contradiction taken for granted by antitheistic thought presupposes the absolute for its operation. Antitheism presupposes theism. One must stand upon the solid ground of theism to be an effective antitheist. (Cornelius Van Til, A Survey of Christian Epistemology, p. xi)

“Antitheism presupposes theism” is one of Van Til’s best lines, because it captures in a nutshell the genius of presuppositional apologetics. It’s not merely that theism is true; it’s not merely that theism can be shown to be true; it’s that theism can be shown to be true by any attempt to prove it false. One can prove theism to be false only if, as a matter of fundamental metaphysical fact, theism is true — which is just to say that antitheism is self-defeating.

The paper I co-authored with Greg Welty gives one line of argument (there are others) in support of Van Til’s pithy and provocative slogan. As we conclude:

[I]f the laws of logic are metaphysically dependent on God, it follows that every logical argument presupposes the existence of God. What this means is that every sound theistic argument not only proves the existence of God but also presupposes the existence of God, insofar as that argument depends on logical inference. Indeed, every unsound theistic argument presupposes the existence of God. And the same goes, naturally, for every antitheistic argument. The irony must not be missed: one can logically argue against God only if God exists.

The last statement is really nothing more than a paraphrase of Van Til. Moreover, our paper sheds light on how one might understand the term ‘presupposes’ in Van Til’s famous statement. (I don’t claim that this is exactly how Van Til meant it, but I do claim that it’s consonant with his overall apologetic vision.) We have argued that the laws of logic should be understood as divine thoughts — more precisely, as divine thoughts about the essential relations between divine thoughts. Thus the relationship between God and the laws of logic is none other than the relationship between God and God’s thoughts.

On this view, ‘presupposes’ can be cashed out in terms of metaphysical preconditionality: X presupposes Y just in case Y is a metaphysical precondition of X; which is to say that X can be the case only if Y is the case (where Y pertains to some metaphysical state-of-affairs, e.g., the existence of a being with certain attributes). Clearly the existence of God is a metaphysical precondition of there being divine thoughts, just as the existence of humans is a precondition of there being human thoughts. In the absence of humans, there can be no human thoughts; in the absence of God, there can be no divine thoughts. So if we’re correct that the laws of logic must be divine thoughts, the existence of God is a metaphysical precondition of the laws of logic.

I take it that antitheism is more than just atheism. Atheism is simply the rejection of theism. (Some will want to distinguish between negative atheism — the absence of belief in God — and positive atheism — belief in the absence of God.) Antitheism, however, doesn’t merely deny theism; it opposes theism. And one of the ways it opposes theism is through argument. Antitheists oppose theism by arguing that belief in God is false, irrational, irresponsible, dangerous, and all the rest.

Insofar as logical argument depends on laws of logic, antitheism depends on laws of logic. Without laws of logic there could be no antitheism — at any rate, no logical antitheism. But if the existence of God is a metaphysical precondition of the laws of logic, it follows straightforwardly that the existence of God is a metaphysical precondition of antitheism. In other words: “Antitheism presupposes theism.”

One might think that a more modest, quasi-fideistic form of atheism escapes this sort of self-defeat. An atheist of this stripe might put it as follows: “I deny that theism is true, but I don’t think that the non-existence of God can be logically proven or argued. Since my atheism doesn’t depend on the laws of logic, it doesn’t presuppose theism, even if you’re right that the laws of logic presuppose theism.”

No doubt there are some such atheists, just as there are fideistic theists. But while their atheism may not depend on the laws of logic, they will surely rely on the laws of logic in other areas of life, whether they recognize it or not. In any case, it’s not clear that this weak atheism doesn’t depend on the laws of logic in other ways. (Consider, for example, the logical force of the word ‘since’ in the paragraph above.)

Let us suppose, however, that there could be an extraordinarily modest form of atheism that didn’t depend at all on the laws of logic. Could it avoid the sort of presuppositional refutation that Van Til had in mind? I think not. Consider the following reductio argument:

(1) God does not exist. [assumption for reductio]

(2) It is true that God does not exist. [from (1)]

(3) There is at least one truth (namely, the truth that there is no God). [from (2)]

(4) If there are truths, they are divine thoughts.

(5) There is at least one divine thought. [from (3) and (4)]

(6) If there are divine thoughts, then God exists.

(7) Therefore, God exists. [from (5) and (6)]

Obviously the most disputable premise in the argument is (4). So what good reason is there to accept it?

While our paper doesn’t explicitly argue for (4), it nonetheless suggests an indirect argument for it. We argue, in effect, that if there are necessary truths, they should be identified with divine thoughts. But what about contingent truths? Couldn’t the atheist maintain that (1) is a contingent truth and that contingent truths don’t have to be divine thoughts?

There are several problems with such a response. First, Plantinga’s modal ontological argument shows at least that if God possibly exists then God necessarily exists. It follows that the only coherent form of atheism is “Anselmian atheism”: if the claim that God exists is false then it must be necessarily false.

Secondly, and more generally, one’s theory of propositions shouldn’t be more ontologically complex than it needs to be. (Recall that we argue in the paper that truths are propositions, that is, primary truth-bearers.) Shouldn’t we expect all propositions to have the same metaphysical basis, regardless of their modality? It would be a strange theory of propositions which held that some propositions are divine thoughts while other propositions are something else altogether (e.g., human thoughts or brain-inscriptions).

Thirdly, and more decisively, one can argue from the claim that propositions are thoughts (a claim we defend in the paper) that contingent truths must also be divine thoughts. Assume that God’s decision to create was free and contingent, in which case there is a possible world in which there is no creation; a possible world in which only God exists. (For simplicity’s sake I’m ignoring theistic platonist schemes in which there are necessarily existent abstract objects distinct from God.) In that possible world, there is at least one contingent truth: the truth that God freely chose not to create. But if that truth — that true proposition — is a thought, it must be a divine thought (because the only mind is God’s mind). So both contingent and necessary truths — in other words, all truths — should be identified with divine thoughts.

Finally, we can argue that if there are contingent truths, there must also be necessary truths. According to the most intuitive and widely accepted system of modal logic (S5) the modal status of a proposition is the same in every possible world, thus whatever is contingent is necessarily contingent. So for every contingent truth P there is a corresponding necessary truth, namely, that P is not a necessary truth. (There are other arguments in the neighborhood: e.g., for every truth P there is a corresponding necessary truth, namely, that P is either contingently true or necessarily true.)

It therefore appears that any form of atheism that denies the existence of God must presuppose the existence of God. But what about the agnostic, who rejects both theism and atheism? It’s not difficult to see how the argument above can be adapted so as to defeat agnosticism on the same basis:

(1′) I don’t know whether or not God exists.

(2′) It is true that I don’t know whether or not God exists. [from (1′)]

(3′) There is at least one truth (namely, the truth that I don’t know whether or not God exists). [from (2′)]

(4) If there are truths, they are divine thoughts.

(5) Therefore, there is at least one divine thought. [from (3′) and (4)]

(6) If there are divine thoughts, then God exists.

(7) Therefore, God exists.

Moreover, even if the agnostic affirms neither atheism nor theism, he should at least accept that theism is either true or false: either God exists or God does not exist. But then the same line of argument can be launched from that premise (which, we should note, is a necessary truth):

(1”) Either God exists or God does not exist.

(2”) It is true that either God exists or God does not exist. [from (1”)]

(3”) There is at least one truth (namely, the truth that either God exists or God does not exist). [from (2”)]

(4) If there are truths, they are divine thoughts.

(5) Therefore, there is at least one divine thought. [from (3”) and (4)]

(6) If there are divine thoughts, then God exists.

(7) Therefore, God exists.

So we can see that antitheism, atheism, and agnosticism all presuppose theism, if the argument that necessary truths are divine thoughts is sound. In fact, it ought to be clear by now that by the same underlying argument we can show that any ‘ism’ presupposes theism. God’s existence is presupposed by any philosophy, ideology, or belief-system that is committed to at least one truth (whether explicitly or implicitly; even nihilism is implicitly committed to the truth of nihilism).

This leads neatly to another of my favorite Van Til quotes:

It is the firm conviction of every epistemologically self-conscious Christian that no human being can utter a single syllable, whether in negation or affirmation, unless it were for God’s existence. Thus the transcendental argument seeks to discover what sort of foundations the house of human knowledge must have, in order to be what it is. (Cornelius Van Til, A Survey of Christian Epistemology, p. 11)

In this post I have suggested one way in which the core contention of Van Til’s transcendental presuppositionalism can be defended. Both negation and affirmation involve propositions: to affirm is to ascribe truth to a proposition; to negate is to ascribe falsity to a proposition. Without propositions, then, there can be neither affirmations nor negations. And if propositions are none other than divine thoughts, it follows that both affirmation and negation presuppose the existence of God. Without God there could be neither affirmation nor negation, neither argument nor knowledge.

Of course, I have assumed here that the core argument of our paper is cogent. My purpose in this post has not been to defend that argument, but merely to show how its conclusions can be deployed in support of some of Van Til’s most distinctive claims.