Summary

Arguments of this form assume that since something has not been proven false, it is therefore true. Conversely, such an argument may assume that since something has not been proven true, it is therefore false. (This is a special case of a false dilemma, since it assumes that all propositions must either be known to be true or known to be false.) "Lack of proof is not proof."

Examples

1. Since you cannot prove that ghosts do not exist, they must exist.
2. Since scientists cannot prove that global warming will occur, it probably won't.
3. Fred said that he is smarter than Jill, but he didn't prove it, so it must be false.

Proof

Identify the proposition in question. Argue that it may be true even though we don't know whether it is or isn't.