You’ve probably heard it before.

God is an ever receding pocket of scientific ignorance that gets smaller and smaller as time goes on” – Neil deGrasse Tyson

Creationists eagerly seek a gap in present-day knowledge or understanding. If an apparent gap is found, it is assumed that God, by default, must fill it.” – Richard Dawkins

Ignorance of nature’s ways led people in ancient times to invent gods to lord it over every aspect of human life.” – Stephen Hawking

Yes, people used to marvel at thunder and lightning and come to unreasonable conclusions. They did not know what was going on, and they concluded that God (or gods) must be responsible. This is a gap reasoning.

But when someone is looking at the available evidence and coming to a ‘therefore God exists,” it is not a God of the gaps conclusion. Many of the logical arguments concluding with “therefore, God exists” may be invalid, unsound or totally wrong, but they’re not gap-reasoning.

If someone says, “I don’t know… therefore X,” that is gap-reasoning.

If someone says, “Here are several reasons why it is reasonable to conclude that X,” that is not gap reasoning.

Here are some examples of gap reasoning:

  • I do not know how information in the genome arose, but I know that nature did it.
  • I do not know where morality came from, but God must be responsible.
  • I do not know how consciousness arises, but it must be a natural process (like emergence).
  • I do not know how the universe began, but it must be God.

A lot of times, someone’s worldview will dictate what they plug into these ‘gaps’. If someone is a theist, they will probably put God (Yahweh, Allah, etc.) into the gap. If someone is a naturalist, they’ll undoubtedly put a natural process (emergence, genetic mutations, etc.) into the gap. If someone leans more spiritual in nature, they might plug some unknown spiritual dimension (kharma, ancestors, etc.) into the gap.
The most important principle here is that putting something into a gap in our knowledge is not a legitimate form of reasoning.

That being said, arguments for X are not guilty of gap reasoning. As an example, here is one argument for God’s existence (the moral argument) as presented by Dr. William Lane Craig:

  1. If God does not exist, objective moral values and duties do not exist.
  2. Objective moral values and duties do exist.
  3. Therefore, God exists.

This is logical argument, not God of the gaps reasoning. It is using the evidence that we have and coming to a certain conclusion. It is not saying “I don’t know how to account for objective moral values, therefore, it must be God.” Even if you disagree with the conclusion (that God exists), it is not a God of the gaps.

Two final thoughts.

First, it is not unreasonable to say, “I don’t know.” But if there are good reasons to think that there is a logical explanation, embracing ‘I don’t know’ instead of the most reasonable conclusion is not necessarily a virtue. You have to determine why you’d reject a good answer for something before simply rejecting it and replacing it with ignorance.

Second, if your philosophical perspective does not allow a perfectly reasonable explanation in the door, it might be time to re-evaluate your underlying philosophy. I’ve had far too many atheists tell me that God is simply not an explanation worth considering. Not because the evidence is weak, the arguments are fallacious, or there is an alternative explanation… simply because, according to them, God does not exist. Not only is this begging the question, it is substituting a philosophical assertion for actual engagement with the argument. The lack of an atheist answer to X does not mean positing God as an explanation for X is “God of the gaps.”

Additional Resources:
Stand to Reason – “God of the Gaps”
Christian Apologetics Alliance – “The Atheist’s God of the Gaps”
CrossExamined – “Who Really Commits the ‘God of the Gaps’ Fallacy?”
John Lennox – “Not the God of the Gaps, but the Whole Show”
William Lane Craig responding to the ‘God of the Gaps’ objection