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Negative Proof

September 24th, 2009

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Negative Proof (argumentum ad ignorantiam)

classification : informal

If the only evidence for something’s existence is a lack of evidence for it not existing, then the default position is one of skepticism and not credulity.


It is claimed that a premise is true only because it has not been proven false, or is false only because it has not been proven true.Note: Negative Proof is a special case of the fallacy of Denying The Antecedent if we accept the additional premise that observing a phenomenon implies that it exists. (Denying The Antecedent is a formal fallacy of propositional logic.)

Other Names

argument from ignorance
argumentum ad ignorantiam

Note: Irving Copi writes that:

The argumentum ad ignorantiam [fallacy] is committed whenever it is argued that a proposition is true simply on the basis that it has not been proven false, or that it is false because it has not been proven true.[…] A qualification should be made at this point. In some circumstances it can be safely assumed that if a certain event had occurred, evidence of it could be discovered by qualified investigators. In such circumstances it is perfectly reasonable to take the absence of proof of its occurrence despite searching, as positive evidence towards its non-occurrence. (Copi 1953)

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Categories: Logic