Ad Ignorantiam (Appeal to Ignorance)

Description:

The argument offers lack of evidence as if it were evidence to the contrary. The argument says, "No one knows it is true; therefore it is false," or "No one knows it is false, therefore it is true."

Comments:

The phrase "ad ignorantiam" is a Latin phrase that means (just as one would expect), "(appeal) to ignorance." Sometimes, in order to make the claim that "no one knows," the argument insists upon an inappropriately strong standard of proof. I have found the fallacy particularly difficult to classify. I currently classify it with the Errors of Observation. It is like Inductive Hyperbole in that both fallacies draw an inappropriately strong conclusion from relatively weak and indecisive observations.

Examples:

"There is no proof that capital punishment deters violent crime. We can only conclude that it doesn't. Our state is better off without the death penalty."

"Why do elephants paint their toenails red? To hide in strawberry patches! Have you ever seen an elephant in a strawberry patch? No? Well, that proves it works."

Discussion:

In legal reasoning "burden of proof" is an important concept. In criminal cases, the burder of proof is on the prosecutor, i.e. the defendant is "innocent until proven guilty." Even outside the law, it is important to keep track of the point that needs to be established. Do you need to prove your own position is true, or do you merely need to show that it has not yet been proven false? In other words, is the burden of proof on you or on your opponent? If the burden of proof is on your opponent, then showing that there is no good evidence to contradict your position is all you need to do. Good reasoning requires nothing further.

In most cases (outside criminal law, where the burden of proof is determined by principles of justice) the assumption of truth is with the older, more established view, or with the view that most people accept (especially if those people are "experts.") The burden of proof, then, falls on the view that is newer or only held by a minority.

The Ad Ignorantiam fallacy mimics good reasoning by arguing that a position has not yet been shown to be false, which may be a perfectly acceptable argument to make in many cases. However, the Ad Ignorantiam fallacy errs by claiming that the argument - where the burden of proof falls on the arguer - shows that his or her position is actually true, not merely that it has not yet been shown false. Since these two issues are closely related, they are easy to confuse.

Source: John Locke, Essay Concerning Human Understanding, 1690. Locke takes credit for naming this fallacy.

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