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The argument from ignorance,[1] also known as argumentum ad ignorantiam ("appeal to ignorance"[1][2]), or negative evidence,[1] 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[citation needed] or argument from personal conviction[citation needed], 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[citation needed]: 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

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)

The two most common forms of the argument from ignorance, both fallacious, can be reduced to the following form:

  • Because there appears to be a lack of evidence for one hypothesis, another chosen (often opposite) hypothesis is therefore considered likely or proven.
  • Something is currently unexplained, or insufficiently understood or explained, so it is not (or must not be) considered true, and the opposite position is considered likely.

To avoid this fallacy, the onus is on thorough investigation for information about the subject(s) being considered or hypothesized about.

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[3][4], who used it to describe the Argument from Design. He summarizes this argument thus:

I personally cannot imagine a natural sequence of events whereby X could have come about. Therefore, it must have come about by supernatural means.[5]

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 above) 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.

Exception in law

In American jurisprudence and the British common law system, argument from ignorance is appropriate. This reasonable double standard has been re-affirmed by Justice William Brennan in his writing of a 1970 case.[6]

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[citation needed]. 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 evidential burden has been met—and only after this burden is met is the defense obliged to present counter-evidence 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 Scotland, where the jury also has the option to return a verdict of not proven[citation needed].

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 photon anti-correlation experiments,[7] 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 phenomenon 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.[8]

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,[citation needed] but this by no means constitutes definitive proof that the universe is developing according to said theory.

See also


  1. ^ a b c Walton, Douglas (1996). Arguments From Ignorance. The Pennsylvania State University Press. pp. 1. ISBN 0271014741. 
  2. ^ "Argumentum ad Ignorantiam". Philosophy 103: Introduction to Logic. Lander University. 2004. Retrieved 2009-04-29. 
  3. ^ Richard Dawkins. The God Delusion. Houghton Mifflin Harcourt. pp. 128. ISBN 0618680004, 9780618680009. 
  4. ^ April M. S. McMahon. Change, chance, and optimality. Oxford University Press. pp. 159. ISBN 0198241259, 9780198241256. 
  5. ^ Richard Dawkins, Yan Wong. "The Rhizobium's Tale". The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution. Houghton Mifflin Harcourt. pp. 549. ISBN 061861916X, 9780618619160. 
  6. ^ Winship, 397 U.S. 358, 1970
  7. ^
  8. ^ Charles Alfred Coulson (1955) Science and Christian Belief, p 20.

External links

"You have no evidence that there ISN'T a teapot on the moon, so there is one" - an appeal to ignorance

Argument from ignorance, also known as argumentum ad ignorantiam or appeal to ignorance, is an informal logical fallacy; it asserts that a proposition is necessarily true because it has not been proven false (or vice versa). This represents a type of false dichotomy in that it excludes a third option: there is insufficient data and the proposition has not yet been proven to be either true or false.[1] In debates, appeals to ignorance are sometimes used to shift the burden of proof.

General forms of the argument:

  1. P has never been disproven therefore P is/(must be) true.
  2. P has never been proven therefore P is/(must be) false.

Carl Sagan famously criticized the practice by referring to it as "impatience with ambiguity", pointing out that "absence of evidence is not evidence of absence". This should not, however, be taken to mean that one can never possess evidence that something does not exist (one can possess such evidence). Instead, Sagan's famous quote is a reminder that inferences must be made carefully, and that science makes no claims to absolute certainty, only high probability.



Arguments that appeal to ignorance rely merely on the fact that the veracity of the proposition is not known, or is undetected, to arrive at a definite conclusion. These arguments fail to appreciate that the limits of one's understanding or certainty do not change what is true. This fallacy can be very convincing and is considered by some[2] to be a special case of a false dilemma or false dichotomy in that they both fail to consider perfectly valid alternatives. A false dilemma may take the form:

  • If a proposition has not been disproven then it can't be considered false, therefore it must be considered true.
  • If a proposition has not been proven then it can't be considered true, therefore it must be considered false.

To reiterate, these arguments ignore the fact, and difficulty, that some true things may never be proven, and some false things may never be disproved with absolute certainty.

This fallacy is sometimes confused , and or combined, with logically valid contrapositive arguments. Contrapositives rightly utilize the transposition rule of inference in classical logic to conclude that: To the extent that C implies E then Not-E MUST ALSO imply Not-C. In other words, if a cause always leads to an effect, then absence of the expected effect is evidence of absence of the cause. For example, if we assume the causal proposition that If it's raining outside then the streets will be wet, then we can reason that if the streets are not wet then it is not raining outside. The inference that it cannot be raining outside because the streets are not getting wet is exactly as true, or perhaps exactly as untrue, as the original proposition. The statements are logically equivalent.

Carl Sagan's Contribution

The phrase "absence of evidence is not evidence of absence" can be used as a short hand rebuttal to the second form of the ignorance fallacy (i.e. P has never been absolutely proven and is therefore certainly false!). Most often it is directed at any conclusion derived from null results in an experiment or from the non-detection of something.

File:Carl Sagan
Carl Sagan beside a Viking model

From: The Demon-Haunted World: (Chapter 12 - The Fine Art of Baloney Detection.)

"Appeal to ignorance -- the claim that whatever has not been proved false must be true, and vice versa (e.g., there is no compelling evidence that UFOs are not visiting the Earth; therefore UFOs exist -- and there is intelligent life elsewhere in the Universe. Or: there may be seventy kazillion other worlds, but not one is known to have the moral advancement of the Earth, so we're still central to the Universe.) This impatience with ambiguity can be criticized in the phrase: absence of evidence is not evidence of absence."

In this regard Irving Marmer Copi writes:

"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 as positive proof of its non-occurrence." (Introduction to Logic, Copi, 1953, Page 95)

Therefore, absence of evidence that it rained (i.e. water is the evidence) may be considered as positive evidence that it did not rain. Again, in science, such inferences are always made to some limited (sometimes extremely high) degree of probability.

Related terms

Contraposition and Transposition

Contraposition is a logically valid rule of inference that allows the creation of a new proposition from the negation and reordering of an existing one. The method applies to any proposition of the type If A then B and says that if you negate all the variables and switch them back to front you will get a new proposition i.e. If Not-B then Not-A that is just as true as the one you started out with and that the 1st implies the 2nd and the 2nd implies the 1st.

Transposition is exactly the same thing described in a different language.

Absence of evidence

Absence of evidence is the absence, or lack of, any kind of evidence that may show, indicate, suggest, or be used to infer or deduce a fact.

Evidence of absence

Evidence of absence is evidence of any kind that shows, indicates, suggests, or can be used to infer or deduce the non-existence or non-presence of something. In some sense "absence of evidence is sometimes evidence of absence". For instance, absence of evidence that there are malignant cells is evidence of absence that there is cancer. At the same time, since sometimes "absence of evidence may not be evidence of absence," logically the link between the two cannot be considered a universal pattern. For example, absence of evidence that mobile phones are always harmful for humans does not mean evidence of absence. The evidence may or may not arise at a later date. In general, whenever observations are noisy or not complete, we should consider "absence of evidence" and "evidence of absence" are two different propositions.

Negative evidence

Negative evidence is sometimes used as an alternative to Absence of evidence and is often meant to be synonymous with it. On the other hand, the term may also refer to evidence with a negative value, or null result equivalent to evidence of absence. It may even refer to positive evidence about something of an unpleasant nature.

Null result

Null Result is a term often used in the field of science to indicate evidence of absence. Keeping with the example above, a search for water on the ground may yield a null result (the ground is dry), therefore it probably did not rain.

Related Arguments

Argument from incredulity / Lack of imagination

Arguments from incredulity take the form:

  1. P is too incredible (or I can't imagine how P could possibly be true) therefore P must be false.
  2. It's obvious that P (or I can't imagine how P could possibly be false) therefore P must be true.

These arguments are similar to arguments from ignorance in that they too ignore and do not properly eliminate the possibility that something can be both incredible and still be true, or obvious and yet still be false.

Argument from self-knowing (Auto-epistemic)

Arguments from self-knowing take the form:

  1. If P were true then I would know it, in fact I do not know it, therefore P cannot be true.
  2. If P were false then I would know it, in fact I do not know it, therefore P cannot be false

In practice these arguments are often fallacious and rely on the veracity of the supporting premise. For example the argument that If I had just sat on a wild porcupine then I would know it, in fact I do not know it, therefore I did not just sit on a wild porcupine is probably not a fallacy and depends entirely on the veracity of the leading proposition that supports it. (See Contraposition and Transposition in the Related terms section in this article)

Distinguishing Absence of evidence from Evidence of absence

File:Operator at
Carefully controlled conditions can make the difference between proper evidence of absence, or plain absence of evidence (e.g. irrelevant or unusable data)

Absence of Evidence is a condition where no valid conclusion can be inferred from the mere absence of detection, normally due to doubt in the detection method. Evidence of absence is the successful variation: a conclusion that relies on specific knowledge in conjunction with negative detection to deduce the absence of something. An example of evidence of absence is checking your pockets for spare change and finding nothing but being confident that the search would have found it if it was there.

Formal argument

By determining that a given experiment or method of detection is sensitive and reliable enough to detect the presence of X (when X is present) one can confidently exclude the possibility that X may be both un-detected and present. This allows us to deduce that X cannot be present if we receive a null result.

Thus there are only two possibilities, given a null result:

  1. Nothing detected, and X is not present.
  2. Nothing detected, but X is present (Option eliminated by careful research design)

To the extent that option 2 can be eliminated one can deduce, that if X is not detected then X is not present and therefore the null result is evidence of absence.


Absence of evidence

(These examples should contain or represent missing information.)

  • Statements that begin with "I can't prove it but…" are often referring to some kind absence of evidence.
  • "There is no evidence of foul play here" is a direct reference to the absence of evidence.

Negative results

  • When the doctor says that the test results were negative, it's usually good news.
  • Under "Termites" the inspector checked the box that read "no".
  • The results of Michelson–Morley's experiment reported no shift at all in the interference pattern.

Evidence of absence

(These examples should contain definite evidence that can be used to show, indicate, suggest, infer or deduce the non-existence or non-presence of something.)

  • A biopsy showing the absence of malignant cells.
  • The null result found by Michelson–Morley's famous experiment represents "strong evidence" that the luminiferous aether was not present.
  • You very carefully inspect the back seat of your car and lo… no tigers.
  • The train schedule does not say that the train stops here at 3:00pm on a Sunday.

Arguments from ignorance

(Draws a conclusion based on lack of knowledge or evidence without accounting for all possibilities)

  • "I take the view that this lack (of enemy subversive activity in the west coast) is the most ominous sign in our whole situation. It convinces me more than perhaps any other factor that the sabotage we are to get, the Fifth Column activities are to get, are timed just like Pearl Harbor... I believe we are just being lulled into a false sense of security." - Then California's Attorney General Earl Warren (before a congressional hearing in San Francisco on 21 February, 1942)

In the field of science

  • You look in the back seat of your car and lo... no adult sized kangaroos and then use this negative/null adult sized kangaroo detection results in conjunction with the previously determined fact (or just plain old proposition) that adult sized kangaroos, if present, cannot evade such detection, to deduce a new fact that there are indeed no adult sized Kangaroos present in the back seat of said car. (It's a lot of trouble being rigorous.)

Principles in law

  • The presumption of innocence, if present, effectively removes the possibility that the accused may be both guilty and unproven, from consideration in judgment, and as such the accused is considered as innocent unless proven guilty. (See decision table below)
    1. Innocent and unproven. Judged as innocent.
    2. Innocent and proven. Judged as innocent.
    3. Guilty and unproven. Judged as innocent. (Presumption of innocence)
    4. Guilty and proven. Judged as Guilty. (Innocent unless/until proven guilty is a summary of this and easier to remember.)

Origin of the term

From "Fallacies: classical and contemporary readings By Hans V. Hansen, Robert C. Pinto"

"It is generally accept that the philosopher John Locke introduced the term in his Essay Concerning Human Understanding:"
"Another way that Men ordinarily use to drive others, and force them to submit their Judgments. And receive the Opinion in debate, is to require the Adversary to admit what they alledge [sic] as a Proof, or assign a better. And this I call Argumentum ad Ignorantum" - John Locke


  • Fallacies: classical and contemporary readings By Hans V. Hansen, Robert C. Pinto
  • Introduction to Logic by Irving Marmer Copi.
  • Essay Concerning Human Understanding Book IV - John Locke

See also


External links

  1. redirect Template:relevance fallacies

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