**Proof and Persuasion**

If the conclusion of a sound argument is rejected because of sinful suppression, clearly that’s no fault of the argument. But it does raise the question of the relationship between proof and persuasion. Should we define a proof as an argument that is not only sound but also *persuasive*? The difficulty here is that we’ve now introduced a significant element of human subjectivity. What’s persuasive to me might not be persuasive to someone else.

Tying the notion of proof to persuasion isn’t a very promising route. There are simply too many subjective and circumstantial factors to take into account on that front. So let’s try to get back to some more objective criteria for judging arguments.

Often mathematical proofs are held up as the gold standard of objective proofs. For example, we can prove (using a strategy known as induction) that for every natural number N, either N or N+1 is divisible by two. What people often don’t realize is that mathematical proofs are always constructed within the context of a pre-accepted system: a formal scheme that specifies both axioms (foundational propositions) and rules of inference (by which various other propositions can be deduced from the axioms). Mathematical proofs are always *system-dependent*: the proof is only as good as the underlying system.

So if we’re to take mathematical proofs as our model, what “system” should we use to prove the existence of God? Presumably the rules of inference will be the laws of logic. What about the axioms? Some would insist that the axioms of a proof must be beyond rational question: they must be self-evidently true, or indubitable, or logically undeniable, or directly observable by the senses. These are the sort of axioms that *everyone* should accept.

This sounds promising, but even these criteria face objections. Intelligent and well-informed people have disagreed over which truths (if any) are self-evident, indubitable, and logically undeniable. And different people have different sense observations. The quest for universally acceptable premises comes unstuck again.

**Certainty, Circularity, and Social Security Cards**

Also inspired by mathematical proofs is the idea that a proof must have an *absolutely certain* conclusion: its conclusion simply cannot be rationally denied. However, the conclusion of a proof cannot be more certain than its premises; thus an argument with an absolutely certain conclusion must have absolutely certain premises. Does our test-case argument fit that bill?

I would say that anyone who denies there are objective, culture-transcending moral duties is irrational. (I’d argue this is presupposed by Paul’s argument in Romans 1-2.) Anyone who denies those moral duties is either lying, self-deceived, or suffering from cognitive dysfunction. But that’s a distinctively Christian perspective, so now we’re back to the problem of circularity.

As for the first premise of our argument, the conditional premise, I think a very strong case can be made that objective moral duties necessarily depend on God—yet the possibility remains, however slight, that we’ve overlooked something. We can’t claim absolute, knock-down, drag-out certainty for that premise. But does proof really demand *absolute* certainty?

Soon after I relocated from Britain to the United States, I had to visit the local Social Security Administration office to apply for a Social Security Number. The nice lady behind the counter required me to prove several things, so I showed her some documentation, including my British passport, my work visa, my immigration card, and a letter from my employer. But had I really *proven* anything to her?

It’s logically possible that the documents were elaborate forgeries. But how reasonable would it have been for her to demand more rigorous proof? Should I have eliminated every logical possibility that would undermine or contradict my claim, including the possibility that I was using a Jedi mind-trick or that she was actually in a dream?

However tempting it may be to set a high bar for a proof, the higher we set the bar the less reasonable it becomes to *demand* such a proof. So where does that leave our original question? Can we give any useful answer to it?

**Person-Dependent Proofs**

Here is my modest proposal: We should think of proofs in terms of *proofs for a particular person*. In much the same way that mathematical proofs are system-dependent, so proofs of the existence of God need to be seen as *person-dependent*. The question “Can we prove the existence of God?” then becomes “Can we prove the existence of God *to so-and-so*?” My suggestion is that if we can show, without begging the question, that the existence of God logically follows from propositions that a person already accepts, or is willing on reflection to accept, then we have indeed proven the existence of God *to that person*. If they fail to see that the existence of God follows from what they already believe or take for granted, or if they prefer to abandon other beliefs rather than to affirm the existence of God, the problem doesn’t lie in the proof.

What does this mean for our test-case argument? If we understand proof along the lines I’ve suggested, the argument is indeed a proof *for particular people*, not necessarily for everyone. What’s more, on this understanding there are *numerous* proofs of God’s existence. There are many arguments that demonstrate the existence of God from beliefs or assumptions that people already hold. (Consult the resources listed below for examples.) Some of these proofs might be deemed more effective or more persuasive than others, depending on the target audience, but as we’ve seen, proof and persuasion are two distinct things.

**Yes, We Can Prove God Exists**

So yes, we can prove the existence of God; but how exactly we prove the existence of God will depend on the particular person we’re dealing with and what they’re willing to grant.

There is, however, another question I think we should also ask: “Do we *need* to prove the existence of God?” My short answer: “No, but it’s still important to be able to do so.” I take the view, following John Calvin and other Reformed scholars, that Romans 1:18-32 teaches a universal knowledge of God: a *sensus divinitatis* that is part of our human nature. On this view, every human being possesses a natural knowledge of the living and true God, even though they sinfully distort and suppress that knowledge. It’s precisely this fact that serves as the basis for God’s universal judgment. People don’t *need* to have the existence of God proven to them by us. Natural revelation, we might say, is proof itself and proof enough. It’s as though God is continually showing his self-certified “documentation.” Furthermore, I agree with the so-called Reformed epistemologists (Alvin Plantinga being the most well-known) that we hold many beliefs, including many beliefs about God, in a “basic” way; that is, not on the basis of proofs or arguments or inferences from observational evidence. So no one *needs* to be able to prove the existence of God in order to have a rational belief in God.

Nevertheless, proofs of God’s existence, when formulated consistently with biblical revelation, can still serve many useful purposes. They can clarify our understanding of God, his attributes, and his relationship to the creation; they can increase our appreciation of God’s majesty and our utter dependence on him; they can help to neutralize the objections of unbelievers and the doubts of believers; and they can expose the irrationality and self-deceit of unbelief—all to the glory of God