The appeal to ignorance (argumentum ad ignorantiam) is an error in thinking which argues that a conclusion is true because there is no evidence against it, or that a conclusion is false because there is no evidence in its favour.

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Let’s take one of these cases: supporting the validity of a conclusion because there is no evidence that it is false. Let’s say that a company manager claims that all his employees enjoy his management style because he has never heard them complain. But, if the manager did not hear the employees complaining, it cannot be logically deduced that they would not complain or have no reason to do so. A lack of observed evidence does not mean that something did not happen.

Equally, an appeal to ignorance is used when arguing against an idea only because there is no evidence that it is true: “We have no evidence that angels exist. Therefore there are no angels.”

The logic of the appeal to ignorance is based on a modus tollens deduction being considered valid. This presupposes the following premises: 1) if p, then q; 2) if there is no p (from which results the conclusion) 3) then there is no q. For example: 1) If the sensor detects an intruder, an alarm is triggered. 2) But the alarm did not go off. 3) Therefore there is no intruder.

But the appeal to ignorance goes beyond the limits of the logical validity of modus tollens in three ways. First, ignorance is used as a cognitive heuristic1, an adaptive decision-making strategy in a given situation used to make quick and intuitive a priori judgments. This is seen in the case of stereotyping, when we assume that a member of a group has certain group traits, without checking.

Second, there is ignorance as systematic, intentional thinking. Sometimes we seek to gather evidence in favour of our own opinions or beliefs, deliberately resorting to ignorance. Let’s say M grew up in a family with X religion. He loves his family and wants to preserve its traditions and values. He meets N, with Y religion. M does not want to know about Y religion, or discuss it with N.

In the end, there is ignorance as unsystematic but intentional thinking, in which no evidence is necessarily sought, but there is simply an ontological laziness: “This is how I was born, this is how I will die”; “Believe and do not doubt.”

Contemporary, critical directions

The appeal to ignorance has been referred to more and more over time, especially in recent decades. Argumentum ad ignorantiam2 does not appear in Aristotle’s list of sophisms. In the contemporary arena of critical thinking, logic, rhetoric or persuasion, however, this type of argumentation has been theorised and classified as an informal error of relevance, in three ways: 1) if there is no obvious fact that is already accepted, then X does not exist; 2) if there is no proof, then X does not exist and 3) if it is not known, then X does not exist.3

Types of appeals to ignorance

One type of appeal to ignorance can be described as “an unjust attempt to place the burden of proof in a dialectical game.”4

X (where X = you are to blame for what happened)

Why X?

Why not X?

Usually, the burden of proof falls on the one who makes a statement. You can’t accuse your friend of stealing your phone and ask him to prove he didn’t steal it. The burden of proof is on you, the accuser, and waiting for him to provide evidence of his innocence is a shift in the responsibility of the evidence.

The purpose of this type of sophisticated argument is to raise doubts. It is often the case that in a debate, ignorance is used when one party tries to throw the burden of proof on the other. The party who made the claim then has a lighter burden than the burden of providing evidence.

Another type of this appeal is seen in asking a question: Couldn’t it be like X? In this case, in the absence of an answer to the contrary, X is placed in the limelight. Using a controversial episode from history, one can imagine the following example: Rome burned down. Are Christians to blame? In the absence of an answer that can excuse them, Christians are the only ones available to blame.

When does the absence of evidence prove something?

There are situations when the absence of evidence can prove a statement right. It is good to know that this scenario is possible only when we talk about standard methods of producing evidence. Presumptive reasoning considers the possibility of changing the initial conclusion if new evidence is provided.

For example, someone is interested in buying a home and wants to know if they will have problems with mould. They hire a specialist who tells them that there is no evidence of mould in the house and, based on the lack of evidence of the presence of mould, they conclude that the future owner will not have problems with mould. This is not an appeal to ignorance, because the negative deduction (lack of traces of mould) is based on an assessment, on an analysis of the obvious fact.

Instead, the appeal to ignorance is based only on the fact that there is no evidence for the statement made. If someone says there is no mould in the house because he has not seen mould, this argument is an example of an appeal to ignorance. Therefore, in the first case, an “appeal to evidence” is used (an examination leading to the conclusion that there are no conditions necessary for mould to grow), while in the second case “evidence of non-evidence” is used.5

Paths of ignorance

There are three main types of arguments made out of ignorance:

First, presumptive reasoning, which leaves room for the conclusion to change according to the evidence. Defendants enjoy the presumption of innocence, until proven otherwise (“innocent until proven guilty”).

The second situation is epistemic closure6, which is created when we assume that what we know is complete.

The last of the three situations is self-epistemic reasoning, which starts from the premises of one’s own pool of knowledge and from the conception that someone would know if something had happened. The reasoning is this: if P were true, then I would have known about P, or that P happens. I do not know that P happens, therefore P is false. If drug X had side effects, I would have known. I don’t know of any cases that have had side effects. So it has no side effects.

Ignorance and God

The statement: “Despite our sincere efforts to prove that God does not exist, we have no evidence (or knowledge) that God does not exist. Therefore God exists” is also an appeal to ignorance.

In other words, it is established that universal, empirical sentences “without restrictions”7 can be disproved on the basis of a single counterexample. To prove the statement that “all crows are black” we should do an analysis of all crows in the past, present and future, which is physically impossible. However, based on the absence of evidence to the contrary, we can provisionally say that all crows are black. It is the type of reasoning atheists often use: We have not had and do not have evidence that God exists, and we do not know the future. Therefore God does not exist.

Both the theist and the atheist make an error of ignorance when asserting the existence/non-existence of God, but there is at least one aspect that differentiates them: the two will always be in an “asymmetrical position.”8

While theists need evidence (the burden of proof is on them), atheists defend their position by undermining theistic arguments. However, the apparent victory of atheists (“until theists bring evidence, God does not exist”) ignores one aspect: the call to the future. Ignorance does not take into account their appeal to the future.

If it has not been proved that God exists in the past or in our times, how can we say that God does not exist if we do not know the future? What if He reveals Himself in the future? The Bible tells us that a day will come when this will happen, and then “every eye will see Him.” Moreover, this type of argument ad ignorantiam is similar to a hypothetical situation 500 years ago in which someone might have said, based on experience, that a piece of metal cannot fly. Today, not only do planes fly, with their tons of metal, but a metal vessel has even reached the Moon.

And if there is not enough data for any of the theories, shouldn’t our thinking be suspended? For the time being, Christians do not remain in the realm of ignorance, but of faith, and its evidence. If we cannot prove mathematically that God exists or does not exist, we still have the opportunity to believe.

Homo nonignorantus ex Deus est

There is a difference between being ignorant in certain areas (that is, unknowing) and proliferating ignorance as an argument. The absence of evidence against a statement is not sufficient for it to be true. On the other hand, what we do not know may be true. Lack of evidence is not proof. Science and religion alike could not exist if we were all sick with the disease of ignorance.

The philosopher Peter Kreeft suggested that “ignorance can never be a premise or a reason. The premises must express knowledge-type statements. Nothing comes of nothing.”5 And the appeal of ignorance is no exception. Argumentum ad ignorantiam is an ignorant call. Man was endowed with the right to knowledge, not ignorance: homo nonignorantus ex Deus est.9

Enhance your critical thinking. Read more of our articles on the topic.

a method of learning or solving problems that allows people to discover things themselves and learn from their own experiences.
Latin for ”appeal to ignorance”.
H. Vilhelm Hansen, «Locke and Whately on the Argumentum ad Ignorantiam», în Philosophy & Rhetoric, vol. 31, no. 1, 1998, p. 56.
Benjamin W. McCraw, «Appeal to Ignorance», în 100 of the Most Important Fallacies in Western Philosophy, Robert Arp, Steven Barbone, Michael Bruce, editori, Wiley-Blackwell, Oxford, 2019, p. 107.
Donald Sanchez, «Logical Fallacies 101: Ad Ignorantiam», Southern Evangelical,
Douglas Walton, «Nonfallacious Arguments from Ignorance», în American Philosophical Quarterly, vol. 29, nr. 4, oct. 1992, p. 382,
Giovanni Mion, «God, ignorance and existence», în International Journal for Philosophy of Religion, vol. 72, no. 2, 2012, p. 86.
Ibidem, p. 87.
Latin for: ”the unignorant man comes from God”.