This article covers both the 'Argument from ignorance' and the 'Argument from incredulity'.

The argument from ignorance, also known as argumentum ad ignorantiam or argument by lack of imagination, is a logical fallacy wherein a claim is made that lack of evidence for one scenario is instead evidence for another scenario, without additional evidence for the other scenario. Two common forms of the argument are: "if something is currently unexplained then it did not (or could not) happen," or that if evidence of something has not been proven to a person's satisfaction, then it cannot exist. An adage regarding this fallacy is "absence of evidence is not evidence of absence": not having evidence for something is not proof that that something does not exist. Similarly, merely not having evidence for a particular proposition is not proof that another alternative is instead the case--it is in fact simply lack of evidence, and nothing more. Logic, from Classical Greek λόγος (logos), originally meaning the word, or what is spoken, (but coming to mean thought or reason) is most often said to be the study of criteria for the evaluation of arguments, although the exact definition of logic is a matter of controversy among philosophers. ... The term fallacy is used in two senses. ... An adage is a short, but memorable saying, which holds some important fact of experience that is considered true by many people, or it has gained some credibility through its long use. ...

Argument from ignorance is similar to, but not necessarily equivalent to, the argument from personal incredulity (also known as argument from personal belief or argument from personal conviction), where a person asserts that because they personally find a premise unlikely or unbelieveable, it can be safely assumed not to be true. An argument from personal incredulity is the same as an argument from ignorance if, and only if, the person making the argument has solely their particular personal belief in the impossibility of the one scenario as "evidence" that the alternative scenario is true (i.e., the person lacks evidence specifically for the alternative scenario). Look up Premise in Wiktionary, the free dictionary Premise (from the Latin praemisus, meaning placed in front) can refer to: A premise (also premiss in British usage) is a statement presumed true within the context of a discourse, especially of a logical argument. ...

The types of fallacies noted above should not be confused with the reductio ad absurdum method of proof, in which a genuine logical contradiction of the form "A and not A" is used to disprove a premise. Reductio ad absurdum (Latin for reduction to the absurd, traceable back to the Greek ἡ εις άτοπον απαγωγη, reduction to the impossible, often used by Aristotle) is a type of logical argument where we assume a claim for the sake of argument, arrive at an absurd result, and then conclude the original assumption must... Look up Proof on Wiktionary, the free dictionary The word proof can mean: Shit and wanker originally, a test assessing the validity or quality of something. ... Broadly speaking, a contradiction is an incompatibility between two or more statements, ideas, or actions. ... Look up Premise in Wiktionary, the free dictionary Premise (from the Latin praemisus, meaning placed in front) can refer to: A premise (also premiss in British usage) is a statement presumed true within the context of a discourse, especially of a logical argument. ...

Argument from Personal Incredulity

In an Argument from Personal Incredulity or Argument from Ignorance, the speaker considers or asserts that something clearly proven to be accurate is nonetheless false, implausible, or not obvious to him personally (or that something clearly not proven to be accurate is nonetheless true); or he attributes such a belief to the world generally; examples of the above are, "It is hard to see how...," "I cannot understand how...," or "it is obvious that...". The speaker will sometimes continue by using this assertion, without any logical foundation or empirical evidence to support its validity, as a premise which then "evidences" and supports his conclusions, despite that it is merely an untested assertion which still needs its own evidence in order for any conclusions which are based upon it to be logically valid.

Inductive usage

Many 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 descibes 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 (which epistemological foundationalism is closely related to, and intertwined with) are still debated. In dialectic, the term logical fallacy properly refers to a formal fallacy: a flaw in the structure of a deductive argument which renders the argument invalid. ... It has been suggested that this article or section be merged with Academic publishing. ... For the medical term see rigor (medicine) Rigour (American English: rigor) has a number of meanings in relation to intellectual life and discourse. ... Look up Premise in Wiktionary, the free dictionary Premise (from the Latin praemisus, meaning placed in front) can refer to: A premise (also premiss in British usage) is a statement presumed true within the context of a discourse, especially of a logical argument. ... Irving Marmer Copi (born Copilowish, July 28, 1917 – August 19, 2002) was an American philosopher, author, and logician. ... In probability and statistics, if a bias exists it means that the processes involved are not totally random, or one outcome is favoured over others. ... Deductive reasoning is the process of reaching a conclusion that is guaranteed to follow, if the evidence provided is true and the reasoning used to reach the conclusion is correct. ... This article is about induction in philosophy and logic. ... This article or section should include material from Episteme Epistemology (from the Greek words episteme=science and logos=word/speech) is the branch of philosophy that deals with the nature, origin and scope of knowledge. ... ...

Description

Irving Copi writes that: Irving Marmer Copi (born Copilowish, July 28, 1917 – August 19, 2002) was an American philosopher, author, and logician. ...

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 proved false, or that it is false because it has not been proved true. He adds, 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)

To support this, one might add a third case, the argument that something is false or true because the speaker cannot (or finds it hard to) conceive otherwise. This argument by lack of imagination is sometimes expressed in the form "Y is absurd (because I can not imagine it), therefore it must be untrue," or "It is hard to see how..." [ie I personally cannot see, or lack imagination, how], and is sometimes confused with the logically valid method of argument, reductio ad absurdum. A logical argument using reductio ad absurdum would be framed as "X logically leads to a provably impossible (absurd) conclusion, therefore it must be false." In reductio ad absurdum, it is necessary to show that accepting X implies a contradiction (such as "not X", or "Y and not Y" for some other proposition Y). In an argument from ignorance, the speaker asserts "X implies not Y", where Y is believed to be, but cannot be proven, true, rather than something which is provably contradictory. Reductio ad absurdum (Latin for reduction to the absurd, traceable back to the Greek ἡ εις άτοπον απαγωγη, reduction to the impossible, often used by Aristotle) is a type of logical argument where we assume a claim for the sake of argument, arrive at an absurd result, and then conclude the original assumption must...

Copi's argument concerns the Y condition; That in this case of "X implies not Y" for some other proposition Y, some weight must be given to the probability that the speaker's evaluation of Y is correct. For example, if proposition X is "This man was shot", and proposition Y is "There was no bullet", the speaker's qualification to assert condition Y must be considered. A coroner who had examined the body is most likely qualified to draw this conclusion, but an eyewitness is provably unqualified.

Argument from personal incredulity is very similar, e.g. "I am unable to believe/understand X, therefore it must be false."

Examples

• "I find it hard to imagine a way in which a thousand-ton piece of metal could fly through the air. Therefore, airplanes will never work." (This was a common argument why trains could never work, it was "obvious" that if one travelled fast, the air would be blown away too fast to breathe)
• "It is difficult to see how monkeys can be intelligent because they cannot speak." (Argument from personal belief: it may be difficult for the speaker. The fallacy is, perhaps it could be true despite how "difficult" it is for the speaker to believe. Or perhaps it is not difficult for some other experts to believe)
• "You can't prove your views, so don't argue with me!" (a common argument from ignorance - the fact that the other person may not be able to show evidence to 'prove' their side (in whatever way is demanded) does still not necessarily mean in the slightest that their view is wrong)
• In his book Probability of God, Bishop Hugh Montefiore casts doubt on neo-Darwinian evolution with the following statement: If polar bears are dominant in the Arctic, then there would seem to have been no need for them to evolve a white-coloured form of camouflage. This argument from lack of imagination was famously dismissed by the evolutionist Richard Dawkins, who wrote that if the writer had thought to imagine a black polar bear trying to sneak up on a seal in the arctic, he would see the evolutionary value of such fur.
• "The solar system must be younger than a million years because even if the sun was made of solid coal and oxygen it would have burned up within that time at the rate it generates heat" (an argument from ignorance, from 19th Century encyclopedias, based on the assumption that because there was no known means at that time of producing heat more efficient than coal, this logically put a limit on the Sun's possible age. In fact in the 20th Century with the discovery of radioactivity and nuclear fusion, the sun's age was more correctly dated at many billions of years old instead. The 'ignorance' in this case was the omission of considering whether there might be a more efficient generator of heat that has not yet been discovered, which had not been taken into account.)
• "This city can't handle public transportation because we don't have room for any train tracks." (the speaker fails to consider, or is ignorant of the possibility, that there might be other means of providing public transportation, such as buses, as well as the city's ability to appropriate land or excavate a tunnel, which would make it possible)

The modern evolutionary synthesis (often referred to simply as the modern synthesis), neo-Darwinian synthesis or neo-Darwinism, brings together Charles Darwins theory of the evolution of species by natural selection with Gregor Mendels theory of genetics as the basis for biological inheritance. ... A speculative phylogenetic tree of all living things, based on rRNA gene data, showing the separation of the three domains, bacteria, archaea, and eukaryotes. ... Binomial name Ursus maritimus Phipps, 1774 The Polar Bear (Ursus maritimus), aka white bear aka northern bear aka sea bear, is a large bear native to the Arctic. ... This page is a candidate to be moved to Wiktionary. ... Richard Dawkins Clinton Richard Dawkins DSc, FRS, FRSL (known as Richard Dawkins; born March 26, 1941) is an eminent British ethologist, evolutionary theorist, and popular science writer who holds the Charles Simonyi Chair in the Public Understanding of Science at Oxford University. ... Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... For other uses, see Sun (disambiguation). ... (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901–2000 in the sense of the Gregorian calendar (1900–1999 in the... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... Skytrain Bangkok. ...

Law

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. And, by exactly the same reasoning, mere lack of evidence of guilt against any person in existence for every possible crime cannot be necessarily be taken as evidence of innocence--though if this were the accepted standard it would lead towards the absurd scenario where everyone is presumed guilty and all would be required to continually prove their innocence in court. For this reason (among others), modern 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 therefore 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. Criminal law (also known as penal law) is the body of common law that punishes criminals for committing offences against the state. ... Presumption of innocence is a legal right that the accused enjoys in criminal trials in many modern nations. ... Reasonable Doubt was rapper Jay-Zs debut hip hop album, released on June 25, 1996 (see 1996 in music). ...

Also, as a hypothetical example of an "argument from personal incredulity," defined above, suppose someone were to argue:

• I cannot imagine any way for Michael Jackson to have slept with young boys without having sex with them.
• Therefore he must be guilty of the crime of statutory rape.

Merely because the person making the argument cannot imagine how scenario "A" might have happened does not necessarily mean that their 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. To meet Wikipedias quality standards, this article may require cleanup. ... The term statutory rape is used when national and/or regional governments, citing an interest in protecting minors, consider people under a certain age to be unable to give sexual consent, and therefore consider sexual contact with them to be equivalent to rape regardless of their stated consent. ...

The same principles of logic apply to the civil law, although the required burdens of proof generally are different.

Science

Unexplained phenomena are often an indication that a particular scientific theory is incomplete, or incorrect. For example, the wave theory of light does not explain the photoelectric effect, though it fits well with the results of the double-slit experiment. However, later theories based around quantum mechanics explain both. It would be a mistake to assert that because a phenomenon is unexplained by current scientific theories, it is unexplainable by science. The concept wave is related to a disturbance that propagates through space, often transferring energy. ... The photoelectric effect is the emission of electrons from matter upon the absorption of electromagnetic radiation, such as ultraviolet radiation or x-rays. ... The double-slit experiment consists of letting light diffract through two slits producing fringes on a screen. ... A simple introduction to this subject is provided in Basics of quantum mechanics. ...

References

• Irving M. Copi & Carl Cohen, Introduction to Logic. Prentice Hall College Div; 10th edition (1998). ISBN 0130102024.

See also

• Negative proof