The argument from ignorance, also known as argumentum ad ignorantiam ("appeal to ignorance" , argument by lack of imagination, or negative evidence), is a logical fallacy in which 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.

The argument from personal incredulity, also known as argument from personal belief or argument from personal conviction, refers to an assertion that because one personally finds a premise unlikely or unbelievable, the premise can be assumed to be false, or alternatively that another preferred but unproven premise is true instead.

Both arguments commonly share this structure: a person regards the lack of evidence for one view as constituting proof that another view is true. The types of fallacies discussed in this article should not be confused with the reductio ad absurdum method of argument, in which a valid logical contradiction of the form "A and not A" is used to disprove a premise.