The God-of-the-gaps argument (also known as the God-of-the-gaps fallacy) is a term used in the philosophy of science for an inference to the action of a deity from the observation of a phenomenon which seems miraculous or impossible to understand at the time. The term applies especially to situations for which an adequate scientific explanation (or, at least, the outline of one) has since been discovered which explains the phenomenon in question. The name is actually fairly easy to understand: when a person uses the God-of-the-gaps argument, she is filling in a "gap" in her knowledge about a particular observational phenomenon by appealing to God's existence and actions to help her explain it; in other words, she is making an argument which uses God to fill in the "gaps."
What does the God-of-the-gaps argument propose?
As an example, comets have often been viewed throughout history as harbingers of God's judgment or other significant events by anyone with a superstitious bent. Today, however, we know that comets are merely "dirty snowballs" flying through the Solar System, which glow when they are bombarded by solar radiation. Thus, whereas an ignorant person might be inclined to view these celestial objects as somehow related to God's direct action in His creation, someone educated in light of modern science will immediately recognize that comets have little, if anything, to do with God's activity in the cosmos. In this case, God's actions (say, to indicate His judgment on a particular nation) have been fallaciously used to explain the observation of the comet, while modern science offers a better explanation which simply understands the comet as a natural and regularly occurring aspect of God's created order.
Other examples of this argument could easily be given. However, the general form of the argument looks something like this:
1) A phenomenon (lightning, comet, earthquake, etc.) has occurred for which no scientific (or similar) explanation is currently available.
2) Whenever a phenomenon occurs for which no scientific (or similar) explanation is currently available, God must be the one who caused the phenomenon to occur.
3) God caused the phenomenon to occur.
Stated in this way, the argument is deductively valid. However, it is easy to see why the argument is generally regarded as fallacious: there is just no good reason to think that any phenomenon we observe which we do not understand must automatically be regarded as God's direct, miraculous action in His creation. Premise 1) is clearly true or false depending on when one lives in history: if I were a contemporary of Aristotle, it might be true that no explanation of comets currently existed for me, but it would certainly not be true today that no explanation of comets currently exists. Assuming the truth of Premise 2), this would entail that God was a direct cause of comets in the ancient world, but that comets became a natural phenomenon once we discovered what they truly were! Of course, such a claim would be nonsensical.
But even if we accepted Premise 1), we still would have no good reason to think that Premise 2) is true. Why should it be the case that God's action is always the correct explanation of whatever we do not understand? This is simply a non sequitur, i.e., a fallacy in which the argument assumes an unjustifiable connection, such as Premise 2) does. Moreover, many such arguments throughout history have been used to attribute causation of apparently miraculous phenomena exclusively to God's agency, but have been subsequently refuted when scientific explanations for those same phenomena were developed and validated. As such, the God-of-the-gaps argument clearly fails to establish that God really is the cause of any particular phenomenon, and it is therefore an argument which Christians should not use.
It's worth pointing out that calling the God-of-the-gaps argument fallacious does not rule out God's agency entirely; it simply proves that God should not automatically be regarded as the sole cause of some phenomenon, simply because that phenomenon is not presently understood. For instance, it may be the case that multiple explanations of some phenomenon exist, e.g., comets may be both naturally recurring phenomena and occasionally indicators of God's pending judgment. The failure of the God-of-the-gaps argument to show that God is the sole cause of a phenomenon does not imply that God is not a cause of that phenomenon at all.
This leads to what is sometimes referred to as the "atheism-of-the-gaps argument." Just as the God-of-the-gaps argument fallaciously assigns to any apparently inexplicable phenomenon the direct agency of God, the atheism-of-the-gaps argument fallaciously assumes that God can never play an explanatory role in the characterization of any phenomenon which is not currently understood. The argument is usually couched in terms of the manifold successes of modern science: if naturalistic explanations have proven so successful in describing the world around us, shouldn't we assume that everything we don't understand today will ultimately prove to have such a naturalistic explanation? Of course, the answer is no; only detailed investigation on a case-by-case basis can reveal whether or not God has acted directly and miraculously in any given instance. Just as we cannot assume that whatever we do not understand is due to God's intervention, so we also cannot assume that God has not intervened.
In the end, both the God-of-the-gaps and the atheism-of-the-gaps arguments fail, and for similar reasons. Fortunately, their failure points us forward to a more robust description of how God does or does not interact with His creation in any given instance, and helps to motivate an understanding of the Christian faith which is both scientifically accurate and theologically compelling.
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Truth about Creation