Argument from ignorance
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- 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 in which it is claimed that that a premise is true only because it has not been proven false, or that a premise 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 not to be true, or alternately that another preferred but unproven premise is true instead.
Both arguments commonly share this structure: a person erroneously regards the lack of evidence for one view (or alternately, regards their personal bias against the view) as constituting evidence or proof that another view is instead true. In reality this is not valid evidence or proof, as further described below. The types of fallacies discussed in this article should not be confused with the reductio ad absurdum method of proof, in which a valid logical contradiction of the form "A and not A" is used to disprove a premise.
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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 her or his 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 explained), so it was not, or could not, be true.
- Because there appears to be a lack of evidence for one hypothesis, another chosen hypothesis is therefore considered proven.
An adage regarding this fallacy from the philosophy of science is that "absence of evidence is not evidence of absence": not having evidence for something is not proof that that something does not or cannot be true. 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.
Argument from ignorance is also known by its Latin title of argumentum ad ignorantiam.
Argument from personal incredulity
Two common versions 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 (or claims to be) unable or unwilling to fully consider that it might be true, or is unwilling to believe evidence which does not support her or his preferred view.)
- "That's not what people say about this; people instead agree with what I am saying." (Here the person is asserting that a proposition must be inaccurate because the opinion of "people in general" is claimed to agree with the speaker's opinion, without offering specific evidence in support of the alternative view.)
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 relevant evidence specifically for the alternative scenario).
Quite commonly, the argument from personal incredulity is used in combination with some evidence in an attempt to sway opinion towards a preferred conclusion. Here too, it is a logical fallacy to the degree that the personal incredulity is offered as further "evidence." In such an instance, the person making the argument has inserted a personal bias in an attempt to strengthen the argument for acceptance of her or his preferred conclusion.
- (Also see similar arguments: wisdom of repugnance and argument from emotion)
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 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.
Description
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 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.
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
- "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 is not a valid indication that the other person's view is necessarily wrong)
- "A thousand-ton piece of metal could never float. Ships need to be made of wood, or at least something that floats."
- "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, excavate a tunnel, etc., which might make it possible)
- "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.)
- In his book Probability of God, Anglican 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.
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 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 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.
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 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...").
Science
Unexplained phenomena are often an indication that a particular scientific theory is incomplete, rather than necessarily 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 is a logical mistake to assert that because a phenomenon is unexplained by current scientific theories, it is necessarily unexplainable by science.
Similarly, current lack of evidence about unexplained aspects of evolution (a very fundamental theory upon which the whole of modern biology, biochemistry and even some of modern medicine are dependent) are, from a logical standpoint, correctly taken as indications that the theory of evolution is incomplete, rather than necessarily incorrect. Evolution theory has yet to successfully explain why most species have evolved stepwise in a "punctuated equilibrium" pattern, to explain how species evolved stepwise rather than in continuous random fashion (morphogenesis), and also to explain how the most basic biological forms first developed out of the "primordial soup" (abiogenesis). The lack of current evidence adequate to verify and explain these specific aspects of evolution is, in itself, not properly taken as an indication either that they do not occur, or that there are not natural causes for these empirical phenomena.
References
- Irving M. Copi & Carl Cohen, Introduction to Logic. Prentice Hall College Div; 10th edition (1998). ISBN 0130102024.
See also
de:Argument aus mangelnder Vorstellungkraft he:אד איגנורנטיום hu:Argumentum ad ignorantiam pt:Argumentum ad ignorantiam uk:Argumentum ad Ignorantiam lt:Argumentas iš nežinojimo tr:Argumentum ad ignorantiam