Also called argumentum ad ignorantiam, 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.) Other phrases often employed here, are "lack of proof is not proof"; "absence of evidence is not evidence of absence"; "the lack-of-knowledge inference"; and, "negative proof" or "negative evidence".
- "In 1950, Senator Joseph R. McCarthy responded to a doubting question about the fortieth name on a list of eighty-one case histories he claimed were of Communists working for the United States State Department by saying, 'I do not have much information on this except the general statement of the agency that there is nothing in the files to disprove his Communist connections.'" (Walton, Arguments from Ignorance, pp. 3-4.)
- No one has ever proved that aliens exist, therefore aliens do not exist; or, No one has ever proved that aliens do not exist, therefore aliens exist.
- "Of course Beethoven dictated that symphony to Rosemary Brown: in Playboy the famous authoress Elisabeth Kubler-Ross recently explained that communication with the dead is perfectly possible. Anyway, nobody has ever proved that dead composers don't manifest themselves in this way." (Eemeren, Grootendors, and Henkemans, Fundamentals of Argumentation Theory, pp. 63-4)
- Because we cannot conceive of any sufficient reason that a good and powerful God would allow this or that instance of suffering or evil, God does not exist.
- "Suppose I accuse you of cheating on an exam. 'Prove it,' you say. 'Can you prove that you didn't?' I ask — and thereby commit the fallacy of appeal to ignorance. This fallacy consists in the argument that a proposition is true because it hasn't been proven false. To put it differently, it is the argument that a proposition is true because the opposing proposition hasn't been proven true." (Walton, Arguments from Ignorance, pp. 2-3.)
Identify the proposition in question. Argue that it may be true even though we don't know whether it is or isn't.