Consider all. Test All. Hold on to the good.

Illogic Primer Quotes Clippings Books and Bibliography Paper Trails Links Film

Fallacy of Exclusion and Suppressed Evidence

Important evidence which would undermine an inductive argument is excluded from consideration. “In an induction, the total relevant information needs to be examined. The fallacy occurs when relevant evidence which would undermine an inductive argument is excluded from consideration. The requirement that all relevant information be included is called the principle of total evidence.” (Chhanda, Logic: Informal, Symbolic, and Inductive, p. 48.)

  1. "The police found a dead body with three bullet wounds. It would be a safe, albeit not mathematically certain, conclusion that the person found by the police died because of his gunshot wounds — that is, unless we also knew that the body was missing its head. Although it is still possible that the victim died of gunshot wounds and that the decapitation was inflicted postmortem, it is equally possible that the manner of his death was decapitation and someone administered the bullet wounds postmortem for some other purpose. The fallacy of exclusion forces the decision maker into reaching a false conclusion owing to lack of relevant alternative evidence. (Pedneault, Rudewicz, Silverstone, Sheetz, Forensice Accounting and Fraud Investigation for Non-Experts (John Wiley & Sons: 2012), pp. 215-6)
  2. "Many movie ads, for example, include positive comments from critics, such as 'One of the year's best movies' or 'Hilariously funny — Gene Siskel gave it a thumbs-up.' But when was the last time you saw an ad for a movie that mentioned that Roger Ebert gave it a thumbs down?" (Carrick, The Persuasive Pen, p. 183.) » A related example is the growing phenomenon of movie trailers excising just a word or phrase — "ingenious", "mindbending" — even from reviews which were negative on the whole.
  3. Sandra Silberstein recounts a personal example: "'Imagine the real suffering and grief of people in other countries. The best way to begin a war on terrorism might be to look in the mirror.' One interesting thing I want to observe about that quote is where they chose to begin it. It's a quote from a speech I made at a peace rally at MIT, shortly after September 11th. And I took as my theme the difficulty of imagining the real suffering of other people. And just before that quote they select, I talked about how difficult it is for us to imagine the suffering of the people at the World Trade Center as they were dying. And then I went on from there to invite the audience to try and imagine the suffering of people in Afghanistan if we are to go and declare war on the people of Afghanistan. Of course, the quote is carefully cut so it seems that I only talk about the suffering of people in other countries and not about the suffering of Americans as well..." (Silberstein, War of Words, p. 137.)
  4. "When someone makes an argument but leaves out a particular fact that would contradict the conclusion, they commit the Fallacy of Exclusion. This was committed on a grand scale by a 2004 Oxford study on the abortion-breast cancer link. Considered by many pro-abortion groups as the 'end-all' study on the matter, it consisted of a comprehensive review of over 50 studies on the possible link of abortion to breast cancer. While the conclusion was that no such link existed, the study's lead author, Valarie Beral, admitted to the Washington Post that they excluded many studies that had found a link and contradicted their conclusion, citing only an unproven belief that women with breast cancer 'are more likely then healthy women to reveal they had an abortion, leading to the conclusion that there are more abortions among this group.' The failure to include data that compromised the desired conclusion is evidence of a Fallacy of Exclusion." (Nowak, Guerilla Apologetics for Life Issues, pp. 14-5.)
  5. "Take, for instance, the accounts widely circulated in 2000 about how the tax burden has shrunk to its lowest level in 40 years, with those earning under $30,000 (half of all taxpayers in the year 2000) paying a mere 2 percent of all income taxes. The strong implication of these stories was that the bottom half of taxpayers cannot complain, since they pay such a small amount of all taxes. Overlooked (on purpose? accidentally? out of ignorance?) was the fact that other kinds of taxes are a much greater burden to the bottom 50 percent of income earners than are income taxes. ... [M]ost of these stories failed to note that when all taxes whatsoever are added up, the bottom half of the population pays a higher percentage of their income in taxes than do those in the very high-income groups." (Kahane & Cavender, Logic and Contemporary Rhetoric, pp. 62-3.)
  6. Frequently encountered is the situation where one piece of evidence is discounted because by using it, the result does not fit the forgone conclusion. ... People ... draw conclusions first, then select evidence that supports the conclusions and discount evidence that does not. A common example is the interpretation of land descriptions. People believe they already know what they own; therefore, regardless of the wording in the the description, the conclusion must be what they meant when they wrote it, despite what they actually said. As the court stated in the case of Smart v. Huckins, "it is a matter of fitting the deed to the land, not the land to the deed." (Wilson, Forensic Procedures for Boundary and Title Investigation (John Wiley & Sons: 2008), p. 50).
Give the missing evidence and show that it changes the outcome of the inductive argument. Note that it is not sufficient simply to show that not all of the evidence was included; it must be shown that the missing evidence will change the conclusion. "Anyway, the point of becoming familiar with the fallacy of suppressed evidence is to sharpen one's ability to spot cases in which relevant evidence is being passed over, whether by others or by ourselves. We need, in particular, to learn how to carry through reasoning so as to see whether all likely relevant information has been considered." (Kahane & Cavender, Logic and Contemporary Rhetoric, p. 62.)
On overlooking evidence because of an ideological bias...
Of course, people who suppress evidence often do so inadvertently, one reason that a more all-encompassing label for the fallacy might be overlooked evidence, or perhaps slighted evidence. It's easy, when strongly committed to a particular side of an issue, to pass over arguments and reasons on the other side. In recent years, advocates on both sides of issues such as capital punishment, abortion, the legalization of marijuana, the depiction of violence on TV, and the legalization of prostitution, frequently have been guilty of slighting evidence damning to their side of the issue. Those opposed to "three strikes you're out" legislation, for instance, tend to neglect the ways in which this kind of law might protect society from repeat offenders; those in favor don't like to talk about the high costs associated with keeping people in jail long past the age at which the vast majority of criminals have ceased to commit violent crimes, or about the fact that a great many of those sentenced under these laws have not committed violent or even serious crimes. ¶ We all, of course, sometimes are motivated by more crass considerations than mere overzealousness. Self-interest is a powerful motivator of deliberately shady reasoning, as is self-deception. (Kahane & Cavender, Logic and Contemporary Rhetoric, p. 62.)
On intentional and unintentional suppression...
Fallacies of suppressed evidence may be committed either intentionally or unintentionally. If the author of the argument intentionally omits known relevant information, the fallacy is deliberate deception. The omission of relevant evidence which the author knows may, however, be a simple blunder; the author may simply have forgotten to consider some of the available relevant facts. It may also happen that an author has included among the premises all the relevant information he or she knows, but that others know relevant information of which the author is unaware. Here again, the argument commits a fallacy of suppressed evidence, but again the fallacy is unintentional. The author has done his or her best with the available information. ... Suppressed evidence should not be confused with implicit premises. Implicit premises are assumptions that the author of an argument intends the audience to take for granted. Suppressed evidence, by contrast, is information that the author has deliberately concealed or unintentionally omitted. Implicit assumptions are part of the author's argument. Suppressed evidence is not. (Nolt, Rohatyn, & Varzi, Schaum's Outline of Theory and Problems of Logic, p. 36.)
On the ideal of total evidence...
Some logicians argue that the requirement of total evidence is too stringent, that no argument can incorporate all the known evidence to a given conclusion. With respect to arguments involving very complex issues, this may well be true. For such arguments, the requirement of total evidence is a theoretical ideal, seldom (or perhaps never) attained in practice. Consequently, inductive arguments on very complex issues will generally suffer to some degree from the fallacy of suppressed evidence. the best arguments will be those who minimize suppressed evidence and suppress no evidence that drastically affects the probability of the conclusion. In many simple cases, however, the requirement of total evidence is quite stringently met. (Nolt, Rohatyn, & Varzi, Schaum's Outline of Theory and Problems of Logic, p. 37.)
On whether it is a logical fallacy, strictly speaking...
For example, Hurley cites a case in which a used car salesman sells a car to a woman, but fails to tell her that the odometer had rolled around twice and that the engine had two cracked pistons and a burned valve. Hurley claims that the salesman's argument in this case commits the fallacy of suppressed evidence, where an argument presents evidence for a conclusion but ignores stronger evidence that supports a different conclusion. In this case, we can say that the salesman lied about the engine and, therefore, that he has acted unethically. ... But has he committed a logical fallacy, in particular, the fallacy of suppressed evidence? ¶ This type of criticism, pointing out that a fallacy has been committed, imposes a requirement on the salesman's argument that it must 'tell the whole truth,' so to speak. His argument must not omit relevant evidence. He has an obligation in the context of the dialogue to present all the relevant evidence, or enough of it so that no stronger evidence supporting any other conclusion is left out. This is actually quite a high standard for an argument to meet in order to be nonfallacious. Leaving out relevant evidence could be an indicator of bias, or it certainly is a good indication that the argument is weak and incomplete. But is the defect a serious enough one in context that we are justified in saying that the salesman has committed a logical fallacy? (Walton, The New Dialectic, p. 230.)
On Misusing the Ellipsis...
An ellipsis is an omission of words, usually indicated by a series of periods. We use ellipses all the time as a matter of convenience or emphasis — to  shorten text or oral statements when space or time is limited, drawing a reader or listener’s attention to what is relevant to the discussion at hand. When used properly, an ellipsis brings focus or brevity without sacrificing meaning. But, like a kitchen knife, it can be twisted in service to a darker purpose. In his satirical classic, Devil’s Dictionary, a work that maliciously mocks hypocrisy and the misuse of language, American author and journalist Ambrose Bierce defined “quotation” as  “[t]he act of repeating erroneously the words of another.” Bierce perhaps had the misused ellipsis in mind; in the hands of a rogue, the ellipsis can turn a speaker’s original meaning on its head. Simply take a quotation, neatly trim away the words that don’t support your argument while leaving in place those that do, and you have embarrassed your opponent and misled your audience. Sadly, the ellipsis, misused, can leave lasting effects; studies from psychology tell us that false statements are notoriously persistent and difficult to counter. Fortunately the misused ellipsis is easy to reveal; one need only consult the original material to reveal the truth. (Levin, "Misusing the Ellipsis" at Mediation Channel, Sep. 11, 2009)