Introduction
The Argumentum Ad Ignorantiam fallacy is a common one. It relies on the lack of evidence for the opposing proposition in order to substantiate itself. The most common application in our modern culture is our legal system. A person is innocent until proven guilty. If the prosecution fails to make the case against the defendant, his failure does not mean that the defendant is innocent - only that the burden of proof has not been met. It does not mean that the defendant did not commit the crime. As a general rule, it is the positive assertion that begins a discussion, and therefore the positive assertion that carries the burden of proof. What is gratuitously asserted may be gratuitously denied.
Definition
The fallacy which seeks prove a proposition because of the lack of evidence for the opposing proposition.
Illustrations
Argument #1: Speaker 1: Can you prove the existence of God? Speaker 2: Can you prove that God does not exist?
Argument #2: Mary was assumed into heaven. The absence of her earthly remains proves it.
Diagnosis
The absence of evidence simply means that we are unable to form a judgement on an argument. The ignorance surrounding the argument obviously cannot be mistaken for "knowledge" since there is, quite literally, nothing there. Appealing to silence might very well be better than nothing at all; but as far as reaching the burden of proof required, it falls considerably short.
Antidote
The key here is to hold the burden of proof on the one making the argument. If someone uses this argument, the appropriate response is to issue an equally unsupported denial. One should never allow another to shift the burden of proof by having to disprove your opponent's statement. One should simply point out that the positive assertion has the burden of proof on it, and the evidence must be produced to support it.
John Pacheco
The Catholic Legate
August 10, 2004