Some more information on "Appeal to Ignorance"
Logic: A Rough Guide
http://chuma.cas.usf.edu/~pinsky/logicguide.htm
Appeal to Ignorance (Proving a Negative): an argument that asserts a claim is true because no one can prove it is wrong; this shifts the burden of proof to the audience or opponent rather than the claimant
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List of common Fallacies
http://www.nobeliefs.com/fallacies.htm
appeal to ignorance (argumentum ex silentio) appealing to ignorance as evidence for something. (e.g., We have no evidence that God doesn't exist, therefore, he must exist. Or: Because we have no knowledge of alien visitors, that means they do not exist). Ignorance about something says nothing about its existence or non-existence.
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Logical Fallacies
http://webpages.shepherd.edu/maustin/rhetoric/fallacies.htm
15) Appeal to Ignorance: The fallacy of appeal to ignorance is the assertion that something must be true because it cannot be proven to be false. According to argument theory, the person making an affirmative claim (a claim about what is true, good, necessary, useful, etc.) Has the burden to prove that claim true. The fallacy of appeal to ignorance attempts to reverse the burden of proof and place it on the person making the negative claim (that something is not true, good, useful, etc.) Our justice system has a safeguard against this fallacy built in to it: the presumption of innocence, or the belief in "innocent until proven guilty). If cases were tried according to the appeal to ignorance, the guilty person would have to prove that he or she did not commit a crime, which is, in many cases, a very difficult thing to do.
I believe that life exists in outer space because nobody has ever been able to prove that it does not.
Senator Baxter has never given any compelling evidence to prove that he is not a communist; therefore it is safe to assume that he is.
Nobody has ever been able to prove conclusively that pornography does not lead to sexual violence. Until they do, we had best regulate its production and distribution.
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Fallacy: Burden of Proof
http://www.nizkor.org/features/fallacies/burden-of-proof.html
Includes: Appeal to Ignorance ("Ad Ignorantiam")
Description of Burden of Proof
Burden of Proof is a fallacy in which the burden of proof is placed on the wrong side. Another version occurs when a lack of evidence for side A is taken to be evidence for side B in cases in which the burden of proof actually rests on side B. A common name for this is an Appeal to Ignorance. This sort of reasoning typically has the following form:
Claim X is presented by side A and the burden of proof actually rests on side B.
Side B claims that X is false because there is no proof for X.
In many situations, one side has the burden of proof resting on it. This side is obligated to provide evidence for its position. The claim of the other side, the one that does not bear the burden of proof, is assumed to be true unless proven otherwise. The difficulty in such cases is determining which side, if any, the burden of proof rests on. In many cases, settling this issue can be a matter of significant debate. In some cases the burden of proof is set by the situation. For example, in American law a person is assumed to be innocent until proven guilty (hence the burden of proof is on the prosecution). As another example, in debate the burden of proof is placed on the affirmative team. As a final example, in most cases the burden of proof rests on those who claim something exists (such as Bigfoot, psychic powers, universals, and sense data). Examples of Burden of Proof
Bill: "I think that we should invest more money in expanding the interstate system."
Jill: "I think that would be a bad idea, considering the state of the treasury."
Bill: "How can anyone be against highway improvements?"
Bill: "I think that some people have psychic powers."
Jill: "What is your proof?"
Bill: "No one has been able to prove that people do not have psychic powers."
"You cannot prove that God does not exist, so He does."