Argumentum ad Ignorantiam

The writer argues that since something has not been proven false, it must be true or that since something has not been proven true, it must be false. The absence of proof can never be proof of anything.

Example:

Although the United States never found evidence of an Iraqi nuclear weapons program, there is no doubt it existed. (And we know this how...)

Strategy: Identify the writer's questionable false (or true) assumption and argue that that it could be true (or false) despite the inability to prove it one way or the other.