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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.


Commonly in an argument from personal incredulity or argument from ignorance, the speaker considers or asserts that something is false, implausible, or not obvious to them personally and attempts to use this gap in knowledge as "evidence" in favor of an alternative view of his or her choice. Examples of these fallacies are often found in statements of opinion which begin: "It is hard to see how...," "I cannot understand how...," or "it is obvious that..." (if "obvious" is being used to introduce a conclusion rather than specific evidence in support of a particular view).

Argument from ignorance

The two most common forms of the argument from ignorance, both fallacious, can be reduced to the following form:
  • Something is currently unexplained or insufficiently understood or explained, so it is not (or must not be) true.
  • Because there appears to be a lack of evidence for one hypothesis, another chosen hypothesis is therefore considered proven.

Irving Copi writes that:
The argumentum ad ignorantiam [fallacy] is committed whenever it is argued that a proposition is true simply on the basis that it has not been proven false, or that it is false because it has not been proven true.[...] A qualification should be made at this point.
In some circumstances it can be safely assumed that if a certain event had occurred, evidence of it could be discovered by qualified investigators.
In such circumstances it is perfectly reasonable to take the absence of proof of its occurrence despite searching, as positive evidence towards its non-occurrence.
(Copi 1953)

Argument from personal incredulity

The common version of the argument from personal incredulity are:
  • "I can't believe this is possible, so it can't be true." (The person is asserting that a proposition must be wrong because he or she is incapable of accepting that it may be true.)
This terminology was introduced by Richard Dawkins, who used it to describe the Argument from Design. He summarizes this argument thusly:
I personally cannot imagine a natural sequence of events whereby X could have come about.
Therefore, it must have come about by supernatural means.

Burden of proof

An important aspect of the ad ignorantiam argument is establishing the burden of proof. While this concept is discussed in the law section of this page, it is important to realize that establishing the burden of proof is important in other arenas as well.

Inductive usage

Inductive usage refers to the extension of an argument to support a wider generalization of a hypothesis, principle, scientific theory, or universal law. Many such uses of the Argument from Ignorance are considered fallacious, especially in academic papers which are expected to be rigorous about their key premises and empirical foundations. However, in some cases (such as that which the noted author Irving Copi describes below) where affirmative evidence could reasonably be expected to be found, but following careful unbiased examination, this evidence has still not been found, then it might become expedient, and sometimes even prudent, to infer that this might suggest (though it does not prove, deductively, it suggests inductively) that the evidence does not exist. Or, where the speaker can reasonably assume that all sane people will agree with a premise (e.g. "The sky is blue"), then he might decide it is unnecessary to provide evidence supporting that assertion; however, these issues (to which epistemological foundationalism is closely related, and with which it is also closely intertwined) are still debated.


In most modern criminal legal systems there is a presumption of innocence, and it is the responsibility of the prosecution to prove (usually "beyond reasonable doubt") that a defendant has in fact committed a particular crime. It is a logical fallacy to presume that mere lack of evidence of innocence of a crime is instead evidence of guilt. Similarly, mere lack of evidence of guilt cannot be taken as evidence of innocence. For this reason (among others), Western legal systems err on the side of caution . Simply the act of taking a defendant before a court is not adequate evidence to presume anything. Courts require evidence of guilt to be presented first, adequate for the court to find that the charge has been substantiated—i.e., that the prosecution's evidentiary burden has been met—and only after this burden is met is the defense obliged to present counterevidence of innocence. If the burden of proof is not met, that does not imply that the defendant is innocent. Hence, in such a case, the defendant is found "not guilty", except in Scotlandmarker, where the jury also has the option to return a verdict of not proven .

Also, as a hypothetical example of an "argument from personal incredulity," defined above, suppose someone were to argue:
  • I cannot imagine any way for Person P to have executed action X without committing a crime Y
  • Therefore, Person P must be guilty of crime Y.

Merely because the person making the argument cannot imagine how scenario "A" might have happened does not necessarily mean that the person's preferred conclusion (scenario "B") is correct. As with other forms of the argument from ignorance, the arguer in this instance has arrived at a conclusion without any evidence supporting the preferred hypothesis, merely for lack of being able to imagine the alternative.

The same principles of logic apply to the civil law, although the required burdens of proof generally are different. As well, these principles of logic apply to the introduction of a given component of a legal case by either a complainant or a defendant. That is, the mere lack of evidence in favor of a proposition put forth by a party in a legal proceeding (e.g., the assertion "she couldn't have left the house and returned in time to do X..." is offered without evidence in support) would not properly be taken as evidence in favor of an alternative explanation (e.g., "she did leave the house and return in time to do X...").


Unexplained phenomena are an indication that a particular scientific theory does not provide a satisfactory model sufficient to explain or predict all outcomes. For example, the wave theory of light does not explain the photoelectric effect, though it successfully predicts the results of the double-slit experiment. However, later theories based around quantum mechanics provide an adequate explanatory model of both.

It is a logical mistake to assert that because a phenomenon is unpredictable by current scientific theories, that a better scientific theory cannot be found that provides an adequate natural explanatory model for the phenomena in question; and that therefore, one must assert that the only viable explanation of the unexplained phenomena is the supernatural action of God. This variant, known as the God of the gaps, is rejected by most theologians because it tries to limit God to the unknown aspects of human knowledge..

However, it is also logically incorrect to assume that because a theory does explain all known relevant phenomena, it must be correct. The fact that no counter-examples are known to exist is not in itself proof of a given theory, since there is always the possibility of some yet-to-be-observed counter-example. For example, there are no known phenomena that are inconsistent with the Big Bang theory . This by no means constitutes definitive proof that the universe actually did originate with the Big Bang.

See also


  1. Charles Alfred Coulson (1955) Science and Christian Belief, p 20.

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