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This article is about errors in reasoning. For the formal concept in philosophy and logic, see formal fallacy. For other uses, see Fallacy (disambiguation).

A fallacy is the use of poor, or invalid reasoning for the construction of an argument.[1][2] It is also used to refer to "an argument which appears to be correct but is not."[3] If an argument is fallacious it does not necessarily mean the conclusion is false.[4][5]

Fallacies are commonly divided into those that are formal and those that are informal. A formal fallacy can neatly be expressed in standard system of logic, for example propositional logic.[1] Conversely, an informal fallacy originates in an other error in reasoning than an improper logical form.[6] Arguments committing informal fallacies may be formally valid, but still be fallacious.[7]

Fallacies of presumption fail to prove the conclusion by assuming the conclusion in the proof. Fallacies of weak inference fail to prove the conclusion due to insufficient evidence. Fallacies of distraction fail to prove the conclusion due to irrelevant evidence, like emotion. Fallacies of ambiguity fail to prove the conclusion due to vagueness in words, phrases, or grammar.[8]

Some fallacies are committed intentionally (to manipulate or persuade by deception), others unintentionally due to carelessness or ignorance.

Formal fallacy[edit]

Main article: Formal fallacy

A formal fallacy is a common error of thinking that can neatly be expressed in standard system of logic.[1] An argument that is formally fallacious is rendered invalid due to a flaw in its logical structure. Such an argument is always considered to be wrong.

The presence of a formal fallacy in a deductive argument does not imply anything about the argument's premises or its conclusion. Both may actually be true, or may even be more probable as a result of the argument, but the deductive argument is still invalid because the conclusion does not follow from the premises in the manner described. By extension, an argument can contain a formal fallacy even if the argument is not a deductive one: for instance an inductive argument that incorrectly applies principles of probability or causality can be said to commit a formal fallacy.

Common examples[edit]

Aristotle's Fallacies[edit]

Aristotle was the first to systematize logical errors into a list. Aristotle's "Sophistical Refutations" (De Sophisticis Elenchis) identifies thirteen fallacies. He divided them up into two major types, those depending on language and those not depending on language.[9] These fallacies are called verbal fallacies and material fallacies, respectively. A material fallacy is an error in what the arguer is talking about, while a verbal fallacy is an error in how the arguer is talking. Verbal fallacies are those in which a conclusion is obtained by improper or ambiguous use of words.[10]

Whately's grouping of fallacies[edit]

Richard Whately defines a fallacy broadly as, "any argument, or apparent argument, which professes to be decisive of the matter at hand, while in reality it is not.[11]

Whately divided fallacies into two groups: logical and material. According to Whately, logical fallacies are arguments where the conclusion does not follow from the premises. Material fallacies are not logical errors because the conclusion does follow from the premises. He then divided the logical group into two groups: purely logical and semi-logical. The semi-logical group included all of Aristotle's sophisms except:ignoratio elenchi, petitio principii, and non causa pro causa, which are in the material group.[12]

Intentional fallacies[edit]

Sometimes a speaker or writer uses a fallacy intentionally. In any context, including academic debate, a conversation among friends, political discourse, or advertising, the arguer may use fallacious reasoning to try to persuade the listener or reader, by means other than offering relevant evidence, that the conclusion is true.

Examples of this include the speaker or writer: diverting the argument to unrelated issues with a red herring (Ignoratio elenchi); insulting someone's character (argumentum ad hominem), assuming they are right by "begging the question" (petitio principi); making jumps in logic (non-sequitur); identifying a false cause and effect (post hoc ergo propter hoc); asserting that everyone agrees (bandwagoning); creating a "false dilemma" ("either-or fallacy") in which the situation is oversimplified; selectively using facts (card-stacking); making false or misleading comparisons (false equivalence and "false analogy); generalizing quickly and sloppily (hasty generalization).[13]

In humor, errors of reasoning are used for comical purposes. Groucho Marx used fallacies of amphiboly, for instance, to make ironic statements; Gary Larson employs fallacious reasoning in many of his cartoons. Wes Boyer and Samuel Stoddard have written a humorous essay teaching students how to be persuasive by means of a whole host of informal and formal fallacies.[14]

Deductive fallacy[edit]

In philosophy, the term formal fallacy for logical fallacies and defined formally as: a flaw in the structure of a deductive argument which renders the argument invalid. The term is preferred as logic is the use of valid reasoning and a fallacy is an argument that uses poor reasoning therefore the term logical fallacy is an oxymoron. However, the same terms are used in informal discourse to mean an argument which is problematic for any reason. A logical form such as "A and B" is independent of any particular conjunction of meaningful propositions. Logical form alone can guarantee that given true premises, a true conclusion must follow. However, formal logic makes no such guarantee if any premise is false; the conclusion can be either true or false. Any formal error or logical fallacy similarly invalidates the deductive guarantee. Both the argument and all its premises must be true for a statement to be true.

Paul Meehl's Fallacies[edit]

In Why I Do Not Attend Case Conferences[15] (1973), psychologist Paul Meehl discusses several fallacies that can arise in medical case conferences that are primarily held to diagnose patients. These fallacies can also be considered more general errors of thinking that all individuals (not just psychologists) are prone to making.

Fallacies of Measurement[edit]

Increasing availability and circulation of big data are driving proliferation of new metrics for scholarly authority,[16][17] and there is lively discussion regarding the relative usefulness of such metrics for measuring the value of knowledge production in the context of an "information tsunami."[18] Where mathematical fallacies are subtle mistakes in reasoning leading to invalid mathematical proofs, measurement fallacies are unwarranted inferential leaps involved in the extrapolation of raw data to a measurement-based value claim. The ancient Greek Sophist Protagoras was one of the first thinkers to propose that humans can generate reliable measurements through his "human-measure" principle and the practice of dissoi logoi (arguing multiple sides of an issue).[19][20] This history helps explain why measurement fallacies are informed by informal logic and argumentation theory.

Other systems of classification[edit]

Of other classifications of fallacies in general the most famous are those of Francis Bacon and J. S. Mill. Bacon (Novum Organum, Aph. 33, 38 sqq.) divided fallacies into four Idola (Idols, i.e. False Appearances), which summarize the various kinds of mistakes to which the human intellect is prone. With these should be compared the Offendicula of Roger Bacon, contained in the Opus maius, pt. i. J. S. Mill discussed the subject in book v. of his Logic, and Jeremy Bentham's Book of Fallacies (1824) contains valuable remarks. See Rd. Whateley's Logic, bk. v.; A. de Morgan, Formal Logic (1847) ; A. Sidgwick, Fallacies (1883) and other textbooks.

See also[edit]


  1. ^ a b c Harry J. Gensler, The A to Z of Logic (2010:p74). Rowman & Littlefield, ISBN 9780810875968
  2. ^ John Woods, The Death of Argument (2004). Applied Logic Series Volume 32, pp 3-23. ISBN 9789048167005
  3. ^ F. H. van Eemeren, Robert Grootendorst (1984). Speech Acts in Argumentative Discussions: A Theoretical Model for the Analysis of Discussions Directed Towards Solving Conflicts of Opinion, p.177. ISBN 9789067650182.
  4. ^ "Fallacies". The Nizkor Project. Retrieved 2013-05-28.  Reprinted from Labossierre, Michael C. (1995). Fallacy Tutorial Pro 3.0. MacinMind Software, Inc. 
  5. ^ "Definition and Types of Fallacies". Retrieved 2013-09-10. 
  6. ^ "Informal Fallacies, Northern Kentucky University". Retrieved 2013-09-10. 
  7. ^ "Internet Encyclopedia of Philosophy, The University of Tennessee at Martin". Retrieved 2013-09-10. 
  8. ^ Hurley, Patrick J. (2005). A Concise Introduction to Logic. Wadsworth. p. 656. ISBN 0534585051. 
  9. ^ "Aristotle's original 13 fallacies". The Non Sequitur. Retrieved 2013-05-28. 
  10. ^ "PHIL 495: Philosophical Writing (Spring 2008), Texas A&M University". Retrieved 2013-09-10. 
  11. ^ Frans H. van Eemeren, Bart Garssen, Bert Meuffels (2009). Fallacies and Judgments of Reasonableness: Empirical Research Concerning the Pragma-Dialectical Discussion Rules, p.8. ISBN 9789048126149.
  12. ^ Coffey, P. (1912). The Science of Logic. Longmans, Green, and Company. p. 302. LCCN 12018756. 
  13. ^ Ed Shewan (2003). Applications of Grammar: Principles of Effective Communication (2nd ed.). Christian Liberty Press. pp. 92 ff. ISBN 1-930367-28-7. 
  14. ^ Boyer, Web. "How to Be Persuasive". Retrieved 12/05/2012.  Check date values in: |accessdate= (help)
  15. ^ a b Meehl, P.E. (1973). Psychodiagnosis: Selected papers. Minneapolis (MN): University of Minnesota Press, p. 225-302.
  16. ^ Meho, Lokman (2007). "The Rise and Rise of Citation Analysis". Physics World. January: 32–36. Retrieved October 28, 2013. 
  17. ^ Jensen, Michael (June 15, 2007). "The New Metrics of Scholarly Authority". Chronicle Review. Retrieved 28 October 2013. 
  18. ^ a b Baveye, Phillippe C. (2010). "Sticker Shock and Looming Tsunami: The High Cost of Academic Serials in Perspective". Journal of Scholarly Publishing 41: 191–215. doi:10.1353/scp.0.0074. 
  19. ^ Schiappa, Edward (1991). Protagoras and Logos: A Study in Greek Philosophy and Rhetoric. Columbia, SC: University of South Carolina Press. ISBN 0872497585. 
  20. ^ Protagoras (1972). The Older Sophists. Indianapolis, IN: Hackett Publishing Co. ISBN 0872205568. 
  21. ^ National Communication Journal (2013). Impact Factors, Journal Quality, and Communication Journals: A Report for the Council of Communication Associations. Washington, D.C.: National Communication Association. 
  22. ^ Gafield, Eugene (1993). "What Citations Tell us About Canadian Research,". Canadian Journal of Library and Information Science 18 (4): 34. 
  23. ^ Stein, Zachary (October 2008). "Myth Busting and Metric Making: Refashioning the Discourse about Development". Integral Leadership Review 8 (5). Retrieved 28 October 2013. 
  24. ^ Kornprobst, Markus (2007). "Comparing Apples and Oranges? Leading and Misleading Uses of Historical Analogies". Millennium - Journal of International Studies 36: 29–49. doi:10.1177/03058298070360010301. Retrieved 29 October 2013. 
  25. ^ Meho, Lokman (2007). "The Rise and Rise of Citation Analysis". Physics World. January: 32. Retrieved October 28, 2013. 
  26. ^ Freedman, David A. (2004). Michael S. Lewis-Beck & Alan Bryman & Tim Futing Liao, ed. Encyclopedia of Social Science Research Methods. Thousand Oaks, CA: Sage. pp. 293–295. ISBN 0761923632. 
  27. ^ Allen, Henry L. (1997). "Faculty Workload and Productivity: Ethnic and Gender Disparities". NEA 1997 Almanac of Higher Education: 39. Retrieved 29 October 2013. 

Further reading[edit]

Historical texts

External links[edit]