Skip to main content

Evidence of Absence

By Paul So ~

We often hear the claim that “absence of evidence is not the evidence of absence”, which is famously quoted by Carl Sagan. WizenedSage made the argument to the contrary and I must agree with him. However, I want to go to the very specific and fundamental reason for why it could be the case that absence of evidence is the evidence of absence. I want to show that the claim must be sufficiently testable in order for the absence of evidence to mean that the claim is implausible (if not false in the strict sense).

evidence of absence
evidence of absence (Photo credit: Genista)
So what do I mean when I say that the claim must be sufficiently testable in order to decide whether the absence of evidence is the evidence of absence? What I mean is that the claim is something that we could either confirm or disconfirm with any kind of relevant evidence. Additionally, the claim must be able make implicit or explicit predictions on what kind of data we would find if the claim is true. If we do find such data as the claim predicts, then the claim is confirmed. However, if we do not find any data, then the claim is disconfirmed.

For example, I make the claim that John’s body is in the coffin which is current underneath his tombstone grave. If this claim is true, then I should find some data which is John’s body in a coffin. However, if I open the coffin to find it empty then I must conclude that the claim “John’s body is in the grave” to be false. In the logical form of modus tollens, if X implies Y but Y is absent, then X is false. Likewise, if the claim implies some kind of data, but we do not find any data, then the claim is false. However, this is possible only if the claim is testable, otherwise if it is not testable then the claim cannot yield any predictions on what kind of data we might find.

However, some people insist the claim about God is not testable; it cannot yield any predictable data. Religious apologists sometimes argue that the claim about the existence of God cannot be tested, but if this is the case, then the claim about God can neither be confirmed nor disconfirmed. If it is the case that God can neither be confirmed nor disconfirmed, then people cannot use any kind of evidence whatsoever. They cannot appeal to the fine-tuning evidence, scriptural evidence, archeological evidence, geological evidence, etc. They cannot say that the God-hypothesis is untestable yet try to test the hypothesis at the same time. This would amount to the idea that God-hypothesis is said to be untestable, but is treated to be testable, which is inconsistent and hypocritical. When the religious apologists try to support the belief of God with any evidence, they are implicitly granting the assumption that the belief of God can be tested, but they build up a double standard in which you cannot disprove the existence of God, but you could support the idea that God exists.

This would make the claim “absence of evidence is not the evidence of absence” a meaningless claim, since for an untestable claim no kind of evidence is possible including the evidence of absence. The religious apologist must at least admit that their claim is testable, otherwise they should not even try to support their belief system with any evidence.

Suppose that they do admit that their claim can be tested, but insist that absence of evidence is not the evidence of absence. At first glance this sounds rights, but by further thinking it isn’t. Consider the following scenario: suppose that I told Jack that if he opens a small box he would find an apple. Jack decides to open the box, but finds an orange instead. In this scenario the contrary evidence (orange) is the absence of supporting evidence, which amounts to the evidence of absence! Thus, the claim “absence of evidence is not the evidence of absence” is not entirely true.

There are certain cases when the claim “absence of evidence is not the evidence of absence” is true. First, it is true when the claim is not sufficiently testable, since there are limits in our technology or ability to find the evidence. For example, String Theory is notoriously difficult to test since it claims that there is a vibrating string-like entity that exists in the smallest scale of the trillionth minuscule or billions times smaller than a quark. It would be very difficult to detect such a string-like entity; we do not have sufficient technology to detect that kind of entity of that size. When there is a limit to technology that cannot procure relevant data, then the claim “absence of evidence is not the evidence of absence” is a fair one.

Second, when the scientist just created the hypothesis she does not have any evidence yet. However the claim “absence of evidence is not evidence of absence” is only trivially true. It is trivially true that in the scientist’s case the absence of evidence does not disconfirm her hypothesis, since she did not test her hypothesis yet. The claim would only have more force when she is testing her hypothesis, but still does not find any evidence.

Third, whenever there is a possibility to collect more potential evidence, it would be too hasty to say that the hypothesis’ lack of evidence disconfirms the hypothesis. We cannot conclude that the hypothesis is false due to lack of evidence, since there are more evidence that we need to look over to make a solid conclusion about the hypothesis. However, the problem knows when the evidence is exhaustive, many times it isn’t obvious. The possible solution is “reasonable doubt”, when we suspect that we have gathered sufficient evidence to come to a certain conclusion. However, this would have to be context-sensitive.

Fourth, if the potential evidences are already destroyed by natural causes, since scientists can account for natural mechanisms or causes that destroy the evidence (i.e. fossils destroyed by tectonic plates, earthquake, rain, etc), then the absence of evidence cannot be the evidence of absence. If the criminal destroys the evidence pertaining to the crime, then forensic science cannot say whether or not the criminal is guilty of the crime. In both cases, there are non-ad hoc explanations as to why the evidence does not exist. By non-ad hoc, I mean there is an independent explanation that we know for fact could be true. We know for a fact that earthquakes can destroy many fossils, we know for a fact that often times the most prudent criminal destroys the evidence. However, if someone says that “fairy exists” and insists that the reason why there is no evidence is because a fairy prevents it, then we cannot believe him since he is using ad hoc explanations. His ad hoc explanations assumes the very thing that is disputed, namely the fairy. Likewise, if someone said the reason why there is no evidence for God is because God is “hiding”, this would be ad hoc since we cannot know whether there is a God to begin with who is hiding.

We have to ask ourselves if the religious claim fits into any of these cases. At first glance, it doesn’t seem like it unless we consider the definition of theism. Theism is the belief of the existence of God who is also divine providence, someone who intervenes or interferes with natural processes or human affairs. The interference or intervention would produce some kind of event that cannot be explained by any natural explanations. If we do not find any event that cannot be explained by natural causes, but can only be explained by supernatural causes (i.e. God), since so many events can be accounted by natural causes, then we have reasons to believe that any event should have some natural (or human) causes rather than supernatural cause. People in the past often claim that there are many things in the universe that has no natural explanation: complexity of life, fine-tuning, success of Christianity, etc. However, we found so many natural explanations for each, to the point that natural explanation has the default position.

Perhaps God explains why the universe came to existence, but we don’t have any evidence to support that.The fact that natural explanations work so well from the past to the present, as opposed to the supernatural explanation, shows that the absence of evidence of supernatural explanations working is the evidence of absence. Just like Jack finds oranges rather than apples in the box, we find natural explanations in the universe rather than the supernatural explanations. Since natural explanations are so ubiquitous, we have little reason to believe that supernatural explanations work. It would be a extraordinary claim that there are some events in Nature that does not have a natural (or human) explanation.

It could be the case that we do not have the technology to test the God-hypothesis; it could be the case that there are so much more evidence that we have not found yet for the existence of God; it could be the case that the evidence for God was already destroyed by God to test our faith; it could be the case that we haven’t really tested the God-hypothesis yet. However, these cases aren’t very strong. Our technology has accelerated over the years to the point that we can accumulate vast amount of evidence in a short period of time, which gives us a clearer understanding of the universe. What we find is that the natural explanations has helped us understand the universe far better than the supernatural explanations, not once has supernatural explanations yielded sufficient evidence or intelligibility. It could be the case that the evidences are destroyed by God, but then again this is pointless since we have no basis in believing that there is a God then we have no basis to believe that God destroyed the evidence. The fact that we have found so many natural explanations for things which use to have supernatural theistic explanations, means that we already indirectly tested the God-claim many years ago.

Does this mean that there really is no God? I think that it is fairer to say that the God hypothesis is improbable then outright false. Even though we have made so much progress, it is not entirely conclusive as to whether or not God exists. However, this does not mean that have to remain entirely agnostic about this. We can say that the claim that God exists is improbable, since given what we know about the universe we find no sign that the existence of God plays any role in explaining how the natural world works. We can believe in black holes, since they explain galactic formation and disappearing stars; we find black holes through light. We can believe in gravity since it explains why things fall and how stars form (gravity attracts bigger hydrogen molecules together to form a hot temperature gas-ball, which attracts more molecules, which makes it bigger and hotter until it becomes a star). However, what does God explain? Perhaps God explains why the universe came to existence, but we don’t have any evidence to support that. Does the absence of evidence in this case mean anything? It just means that we have no explanation yet, but since God-hypothesis has no success in explaining anything to begin with we have little reason to suppose that it’s God.

Overall, the “absence of evidence is not the evidence of absence” is not strictly true in all relevant cases. There are cases when “absence of evidence is the evidence of absence”. In the case of God, I think there are reasons to suppose that the lack of evidence does amount to the evidence of absence. The fact that there is suffering in this world that is no prevented seems to be like an evidence of absence of the existence of God; the fact that complexity of life can be explained by mindless processes seems like an evidence of absence of the existence of God; the fact that the bible is this incoherent text with false or implausible claims seems like the evidence of absence of divine revelation. Sure, there are other cases when we can’t be too sure, but I think there are enough cases about God when there is the evidence of absence, at least that’s my personal view.