The appeal to ignorance argues that a claim is true because it has not been shown false, or false because it has not been shown true. 'No one has proven ghosts don't exist, so they must be real.' 'There's no proof this new additive is harmful, so it's safe.' In both, the lack of knowledge is turned into knowledge. The error is that 'not yet shown' leaves the question open; it does not close it in either direction. The fallacy usually works by quietly shifting the burden of proof onto the other person, as if the doubter must disprove the claim instead of the claimant supporting it. There is one important exception. When a thorough search that would very likely have found something turns up nothing, the absence is real evidence: if a careful inspection of the building found no smoke damage, that is a good reason to think there was no fire inside. The test is to ask how hard anyone has looked and whether they would have found it if it were there. After this Concept you can identify an appeal to ignorance and distinguish it from a genuine absence of evidence after a thorough search.
The appeal to ignorance fallacy is claiming something is true because it has not been proven false, or false because it has not been proven true. It helps you spot weak arguments about aliens, conspi…