appeal to ignorance (fallacy)


appeal to ignorance
Authors A.J. Freeley and D.L. Steinberg note that the "defense against this fallacy [of the appeal to ignorance] is to provide the audience with the knowledge necessary to understand the argument. But this is not always easy" (Argumentation and Debate, 2014). (Bob Thomas/Getty Images)


The appeal to ignorance is a fallacy based on the assumption that a statement must be true if it cannot be proved false—or false if it cannot be proved true. Also known as argumentum ad ignorantiam and the argument from ignorance.

Lack of evidence, says ethicist Elliot D. Cohen, "means that we must proceed with an open mind, keeping open the possibility of future evidence that may either confirm or disconfirm the conclusion in question" (Critical Thinking Unleashed, 2009).


As discussed below, the appeal to ignorance is generally not fallacious in a criminal court where an accused person is presumed innocent until proved guilty.

The term argumentum ad ignorantiam was introduced by John Locke in his Essay Concerning Human Understanding (1690). 

See Examples and Observations below. Also see:

Examples and Observations

  • "The following two arguments attempt to shift the burden of proof:
    - There is intelligent life in outer space, for no one has been able to prove that there isn't.
    - I know that every action we perform is predetermined because no one has proved that we have free will.
    Such fallacious arguments involve an appeal to the emotions in that one hopes to place opponents on the defensive, causing them to believe that the proposed conclusion must be true merely because they cannot prove otherwise. That belief would be irrational, resulting from the feeling of intimidation. In logical argument, it is always the obligation of those who propose conclusions to provide proof."
    (S. Morris Engel, With Good Reason, 3rd ed. St. Martin's Press, 1986)

  • Do Ghosts Exist?
    "Those who assert that ghosts do exist will often support their conclusion by arguing that no one can prove that ghosts do not exist; therefore, ghosts must exist. The lack of evidence or inability to show that ghosts do not exist is used to conclude the opposite. Conversely, those who assert that ghosts do not exist often rely on the same logic. They argue that no one can prove that ghosts exist; therefore, they must not exist. Can you see what is wrong with these appeals to ignorance? The lack of information on an issue cannot be used to support any conclusion—other than the conclusion that we are too ignorant to draw a conclusion.

    "One interesting aspect of the appeal to ignorance is that the same appeal can be used to support two conclusions that are diametrically opposed to each other. This paradox is a telltale clue that appeals to ignorance involve flawed reasoning. It is easy to see what is wrong with appeals to ignorance when the opposite arguments (ghosts exist—ghosts do not exist) are presented together and the lack of evidence on the issue under discussion is obvious. However, when the same fallacy surfaces in more complex debates and the appeal to ignorance is not as blatant, the strategy can be more difficult to recognize."
    (Wayne Weiten, Psychology: Themes and Variations, Briefer Version, 9th ed. Wadsworth, Cengage, 2014) 
  • Senator Joe McCarthy's Appeals to Ignorance
    "In 1950, when Senator Joseph R. McCarthy (Republican, Wisconsin), was asked about the fortieth name on a list of 81 names of people he claimed were communists working for the United States Department of State, he responded that '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.'

    "Many of McCarthy's followers took this absence of evidence as proof that the person in question was indeed a communist, a good example of the fallacy of appeal to ignorance. This example also illustrates the importance of not being taken in by this fallacy. No scrap of relevant evidence ever was presented against any of the people charged by Senator McCarthy, yet for several years he enjoyed great popularity and power; his 'witch hunt' ruined many innocent lives."
    (Howard Kahane and Nancy Cavender, Logic and Contemporary Rhetoric, 10th ed. Thomson Wadsworth, 2006)

  • The Argument From Ignorance in Court
    "In legal argumentation, argument from ignorance is closely associated with what is often called the presumption of innocence in a criminal trial. The prosecution has the burden of proof and must bring forward enough evidence to satisfy the proof standard of beyond reasonable doubt. . . . If the defense can show that there is a lack of evidence to support the prosecution's claim (ultimate thesis to be proved in the trial), then the defense has shown that this claim does not hold up and must be rejected. . . . Thus argument from ignorance is fundamental to the argumentation structure of the trial in the adversary system."
    (Douglas Walton, Methods of Argumentation. Cambridge University Press, 2013)