How does an appeal to ignorance try to establish that a claim is true?

An appeal to ignorance, or ad ignorantiam, is a material fallacy that attempts to establish the truth of a claim based solely on the absence of evidence to the contrary.

Rather than providing positive proof or logical grounds to support a conclusion, this argument asserts that a proposition must be true simply because no one has successfully demonstrated that it is false. For example, one might fallaciously argue that a phenomenon like extrasensory perception is real because it has not been proven otherwise.1

This form of reasoning is considered a fallacy because it fails to provide rational grounds for accepting the conclusion; the lack of evidence against a claim does not constitute evidence for its truth.21