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argument to ignorance (argumentum ad ignorantiam)

The argument to ignorance is a logical fallacy of irrelevance occurring when one claims that something is true only because it hasn't been proved false, or that something is false only because it has not been proved true. A claim's truth or falsity depends upon supporting or refuting evidence to the claim, not the lack of support for a contrary or contradictory claim. (Contrary claims can't both be true but both can be false, unlike contradictory claims. "Jones was in Chicago at the time of the robbery" and "Jones was in Miami at the time of the robbery" are contrary claims--assuming there is no equivocation with 'Jones' or 'robbery'. "Jones was in Chicago at the time of the robbery" and "Jones was not in Chicago at the time of the robbery" are contradictory. A claim is proved true if its contradictory is proved false, and vice-versa.)

The fact that it cannot be proved that the universe is not designed by an Intelligent Creator does not prove that it is. Nor does the fact that it cannot be proved that the universe is designed by an Intelligent Creator prove that it isn't.

The argument to ignorance seems to be more seductive when it can play upon wishful thinking. People who want to believe in immortality, for example, may be more prone to think that the lack of proof to the contrary of their desired belief is somehow relevant to supporting it.

Using this fallacy is a tactic sometimes used to discredit people who can't disprove your claim. For example, when CBS News anchor Dan Rather was challenged about the authenticity of documents that indicated that George W. Bush had not fulfilled his National Guard duty as an honorable man, Rather was accused of using forged documents to discredit the president. Rather couldn't prove the documents weren't forgeries, but that doesn't prove that they were. To argue this way is to make an argument to ignorance. Even now one can find numerous places on the Internet where writers refer to the "forged documents." The documents were never proved to be forgeries. To Bush's defenders, this fact is irrelevant.

further reading  

Browne, M. Neil & Stuart M. Keeley. Asking the Right Questions: A Guide to Critical Thinking (Prentice Hall, 1997).

Carroll, Robert Todd. Becoming a Critical Thinker - A Guide for the New Millennium (Boston: Pearson Custom Publishing, 2000).

Damer. T. Edward. Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments 4th edition (Wadsworth Pub Co, 2001).

Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life, 8th edition (Wadsworth, 1997).

Moore, Brooke Noel. Critical Thinking (Mayfield Publishing Company, 2000).

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