Having one’s argument labeled “God of the gaps” is almost as damaging to one’s credibility as being called a fundamentalist. But what exactly is the issue here?
For example, Christians claim that God created the universe (never mind exactly how). Arguably the universe has a physical beginning. Lacking any naturalistic explanation for this, is it fair to say that we have a supernatural explanation on our hands? “Not so fast!” my friend the skeptic is apt to interject. “You’re about to offer a ‘God of the gaps’ argument.”
When is it appropriate to claim that God is responsible for a phenomenon or event? Gregory Ganssle offers a helpful discussion of “God of the gaps” arguments (gap arguments for short) in a chapter of the recent Blackwell Companion to Science and Christianity. I’ll provide a brief overview below.
Suppose that I offer you the following argument:
(1) Natural means cannot explain event E.
(2) Therefore there is a supernatural explanation of event E.
Have I made a logical error? Of course, there are hidden premises—I have also assumed that event E has an explanation and that said explanation is either natural or supernatural. With these hidden premises, however, the argument is sound. The only question is whether the premises are justified.
Ganssle suggests that the skeptic is likely concerned with premise (1). How do I know there’s no natural explanation? Perhaps I have offered the dreaded argument from ignorance. God forbid! Having no proof that E has a natural explanation does not entail that event E does not in fact have a natural explanation. Such an inference would be logically fallacious. Absence of evidence is not evidence of absence.
However, how would this apply to a Great Dane in the bathroom? Suppose I check in my bathroom and do not see evidence of a Great Dane. Absence of evidence is not evidence of absence. Should I therefore remain agnostic about whether or not there’s a giant dog in the bathroom? By no means! If there were a Great Dane in the bathroom, I would expect to see evidence. Not seeing the evidence, I am justified in concluding that there is probably no Great Dane in the bathroom.
With this in mind, we can refine premise (1) to make it more precise:
(1a) No natural means we know of can explain event E.
(1b) If there were natural means to explain event E, we would probably know that this is the case.
(1c) Therefore probably no natural means can explain event E.
What follows from this? If we also include our reasonable yet hidden assumptions, the argument proceeds as follows:
(2a) There is an explanation of event E.
(2b) Every explanation is either natural or supernatural.
(2c) Therefore, it is probably the case that there is a supernatural explanation of event E.
The argument (1a) to (2c) is logically sound. Most of the controversy likely comes from premise (1b), which Ganssle calls the “relevant conditional.”
A few remarks are in order.
First, this argument does not appeal to ignorance. That’s because premise (1b) requires that one has confidence as to whether a natural explanation is likely to exist. One cannot affirm the relevant conditional (1b) without studying the event E. One must consider the failed natural explanations and the obstacles that prevent the discovery of natural explanations. As such, “an argument of this kind is not about gaps in our knowledge after all … Unless we have sufficient knowledge of natural explanations, we cannot make the inferences in question.”
Second, the skeptic may tell me that the gaps in science are shrinking and my argument is weak as a result. How does the advance of science affect arguments of this sort? This is more complicated.
Likely science will affect how we evaluate the relevant conditional (1b). With greater knowledge, we will be able to see more clearly whether a natural explanation is forthcoming or instead likely to elude us forever. It is unclear to me, however, that science will favour the skeptic over the Christian in this regard (fine-tuning for example).
Science may also reveal new explanations or overturn old ones. This will affect premise (1a). Does that mean this argument is somehow intellectually reckless? Not really. Many good arguments rest on empirical evidence and are falsifiable as a result. Being subject to scientific testing ought to be a virtue.
But recall that the skeptic claims to know that the gaps in science are shrinking. In due course science will triumph and give us an explanation for E. How does the skeptic know that? Perhaps they offer an inductive argument here based on the history of science. Ganssle makes two points here. Science may lend support in either direction as it advances. “We may discover new facts that generate new arguments in favour of supernatural explanations. Surely advances in cosmology have done so in recent years.”
Additionally, “what looks like an appeal to an inductive generalization might serve to conceal an a priori commitment to naturalism.” The skeptic may very well believe that science will come through with a naturalistic explanation since they believe that there are no supernatural explanations. Lacking this bias, I am less likely to fear shrinking gaps.
In summary, Christians ought to be careful to justify both (1a) and (1b). If God is to be invoked due to lack of a natural explanation, one must also demonstrate that we would likely know if such an explanation existed. This takes extra work. Conversely, the skeptic ought to examine their faith in the closing gaps and justify their belief that a natural explanation is forthcoming.
 Gregory E. Ganssle, “‘God of the Gaps’ Arguments,” in The Blackwell Companion to Science and Christianity, ed. J. B. Stump and Alan G. Padgett (Malden, MA: Wiley-Blackwell, 2012), 130–139.
 Ibid., 130.
 Ibid., 131–132.
 Ibid., 132.
 Ibid., 136.
 Ibid., 133.
 Ibid., 134.
 Ibid., 135.