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A fallacy is the use of invalid or otherwise faulty reasoning, or "wrong moves"[1] in the construction of an argument.[2][3] A fallacious argument may be deceptive by appearing to be better than it really is, some fallacies are committed intentionally to manipulate or persuade by deception, while others are committed unintentionally due to carelessness or ignorance. The soundness of legal arguments depends on the context in which the arguments are made.[4]

Fallacies are commonly divided into "formal" and "informal". A formal fallacy can be expressed neatly in a standard system of logic, such as propositional logic,[2] while an informal fallacy originates in an error in reasoning other than an improper logical form.[5] Arguments containing informal fallacies may be formally valid, but still fallacious.[6]

A special case is a mathematical fallacy, an intentionally invalid mathematical proof, often with the error subtle and somehow concealed. Mathematical fallacies are typically crafted and exhibited for educational purposes, usually taking the form of spurious proofs of obvious contradictions.


Fallacies are defects that weaken arguments. Fallacious arguments are very common and can be persuasive in common use, they may be even "unsubstantiated assertions that are often delivered with a conviction that makes them sound as though they are proven facts".[7] Informal fallacies in particular are found frequently in mass media such as television and newspapers,[8] it is important to understand what fallacies are so that one can recognize them in either one's own or others' writing. Avoiding fallacies will strengthen one's ability to produce strong arguments.

It can be difficult to evaluate whether an argument is fallacious, as arguments exist along a continuum of soundness and an argument that has several stages or parts might have some sound sections and some fallacious ones.[9]

Systems of classification[edit]

Because of their variety of structure and application, fallacies are challenging to classify so as to satisfy all practitioners. Fallacies can be classified strictly by either their structure or their content, such as classifying them as formal fallacies or informal fallacies, respectively, the classification of informal fallacies may be subdivided into categories such as linguistic, relevance through omission, relevance through intrusion, and relevance through presumption.[10] On the other hand, fallacies may be classified by the process by which they occur, such as material fallacies (content), verbal fallacies (linguistic), and again formal fallacies (error in inference). In turn, material fallacies may be placed into the more general category of informal fallacies. Yet, verbal fallacies may be placed in either formal or informal classifications; compare equivocation which is a word or phrase based ambiguity, e. g. "he is mad", which may refer to either him being angry or clinically insane, to the fallacy of composition which is premise and inference based ambiguity, e. g. "this must be a good basketball team because each of its members is an outstanding player".[11]

Even the definitions of the classes may not be unique, for example, Whately treats material fallacies as a complement to logical fallacies, which makes them synonymous to informal fallacies, while others consider them to be a subclass of informal fallacies, like mentioned above.


Aristotle was the first to systematize logical errors into a list, as being able to refute an opponent's thesis is one way of winning an argument.[12] Aristotle's "Sophistical Refutations" (De Sophisticis Elenchis) identifies thirteen fallacies, he divided them up into two major types, linguistic fallacies and non-linguistic fallacies, some depending on language and others that do not depend on language.[13][14] 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.[15] An example of a language dependent fallacy is given as a debate as to who amongst humanity are learners: the wise or the ignorant.[16] A language-independent fallacy is for example:

  1. "Coriscus is different from Socrates."
  2. "Socrates is a man."
  3. "Therefore, Coriscus is different from a man."[17]

Whately's grouping[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".[18]

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.[19]

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.

Formal fallacy[edit]

A formal fallacy, deductive fallacy or logical fallacy is a flaw in the structure of a deductive argument which renders the argument invalid. The flaw can neatly be expressed in standard system of logic,[2] such an argument is always considered to be wrong. The presence of the formal fallacy 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.

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.

The term logical fallacy is in a sense self-contradictory, because logic refers to valid reasoning, whereas a fallacy is the use of poor reasoning. Therefore the term formal fallacy is preferred. However, the same terms are used in informal discourse to mean an argument which is problematic for any reason.

The term non sequitur (Latin for "it does not follow") denotes a general formal fallacy, often meaning one which does not belong to any named subclass of formal fallacies like affirming the consequent, denying the antecedent, proof by example, fallacy of four terms, or fallacy of the undistributed middle.

Common examples[edit]

Ecological fallacy[edit]

An ecological fallacy is committed when one draws an inference from data based on the premise that qualities observed for groups necessarily hold for individuals; for example, "if countries with more Protestants tend to have higher suicide rates, then Protestants must be more likely to commit suicide."[20]

Informal fallacy[edit]

An informal fallacy is an argument, which may have a valid logical form (unlike a formal fallacy) and yet fail to be sound because one or more of its premises are false.

Merged from Informal fallacy[edit]

An informal fallacy is a form of fallacy that occurs when the contents of an argument's stated premises fail to adequately support its proposed conclusion.[21][need quotation to verify] Fallacies of this type are the "types of mistakes in reasoning that arise from the mishandling of the content of the propositions constituting the argument";[22] in contrast to a formal fallacy of deduction, the error is not a flaw in the form of the argument. Though the form of the argument may be relevant, it is also the content that is implicated in the erroneous reasoning. So while formal fallacies always guarantee that the resulting argument is invalid, an argument containing an informal fallacy might employ a valid logical form that nevertheless remains rationally unpersuasive.

A special type of informal fallacy is the set of inductive fallacies. Here the most important issue concerns inductive strength or methodology (for example, statistical inference); in the absence of sufficient evidence, drawing conclusions based on induction is unwarranted and fallacious. With the backing of empirical evidence, however, the conclusions may become warranted and convincing (at which point the arguments are no longer considered fallacious).[citation needed]

For instance, the informal fallacy of hasty generalization can be roughly stated as an invalid syllogism. Hasty generalisation often follows a pattern such as:

X is true for A.
X is true for B.
Therefore, X is true for C, D, etc.

While never a valid logical deduction, if such an inference can be made on statistical grounds, it may nonetheless be convincing, this is because with enough empirical evidence, the generalization is no longer a hasty one.

Relevance fallacy[edit]

The fallacies of relevance are a broad class of informal fallacies (see the navbox below), generically represented by missing the point: Presenting an argument, which may be sound, but fails to address the issue in question.

Argumentum ex silentio[edit]

An argument from silence features an unwarranted conclusion advanced based on the absence of data.

Examples of informal fallacies[edit]

Hasty generalization[edit]

Hasty generalization is making assumptions about a whole group or range of cases based on a sample that is inadequate (usually because it is atypical or just too small). Stereotypes about people ("frat boys are drunkards," "grad students are nerdy," "women don’t enjoy sports," etc.) are a common example of the principle.

Post hoc (false cause)[edit]

This fallacy gets its name from the Latin phrase "post hoc, ergo propter hoc," which translates as "after this, therefore because of this." Definition: Assuming that because B comes after A, A caused B. Sometimes one event really does cause another one that comes later—for example, if I register for a class, and my name later appears on the roll, it's true that the first event caused the one that came later, but sometimes two events that seem related in time aren't really related as cause and event. That is, correlation isn't the same thing as causation.

Slippery slope[edit]

Definition: The arguer claims that a sort of chain reaction, usually ending in some dire consequence, will take place, but there's really not enough evidence for that assumption. The arguer asserts that if we take even one step onto the "slippery slope," we will end up sliding all the way to the bottom; he or she assumes we can't stop halfway down the hill.[23]

False analogy[edit]

This error in reasoning occurs when claims are supported by unsound comparisons, hence the false analogy's informal nickname of the "apples and oranges" fallacy.[24]

Measurement fallacy[edit]

Some of the fallacies described above may be committed in the context of measurement. 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).[25][26] This history helps explain why measurement fallacies are informed by informal logic and argumentation theory.

Knowledge value measurement fallacy[edit]

Increasing availability and circulation of big data are driving proliferation of new metrics for scholarly authority,[27][28] 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".[29]

For example, anchoring fallacies can occur when unwarranted weight is given to data generated by metrics that the arguers themselves acknowledge is flawed. For example, limitations of the journal impact factor (JIF) are well documented,[30] and even JIF pioneer Eugene Garfield notes, "while citation data create new tools for analyses of research performance, it should be stressed that they supplement rather than replace other quantitative-and qualitative-indicators."[31] To the extent that arguers jettison acknowledged limitations of JIF-generated data in evaluative judgments, or leave behind Garfield's "supplement rather than replace" caveat, they court commission of anchoring fallacies.

A naturalistic fallacy can occur for example in the case of sheer quantity metrics based on the premise "more is better"[29] or, in the case of developmental assessment in the field of psychology, "higher is better."[32]

A false analogy occurs when claims are supported by unsound comparisons between data points, for example, the Scopus and Web of Science bibliographic databases have difficulty distinguishing between citations of scholarly work that are arms-length endorsements, ceremonial citations, or negative citations (indicating the citing author withholds endorsement of the cited work).[27] Hence, measurement-based value claims premised on the uniform quality of all citations may be questioned on false analogy grounds.

For the next example let us consider Academic Analytics' Faculty Scholarly Productivity Index, which purports to measure overall faculty productivity, yet the tool does not capture data based on citations in books. This creates a possibility that low productivity measurements using the tool may constitute argument from silence fallacies, to the extent that such measurements are supported by the absence of book citation data.

Ecological fallacies can be committed when one measures scholarly productivity of a sub-group of individuals (e.g. "Puerto Rican" faculty) via reference to aggregate data about a larger and different group (e.g. "Hispanic" faculty).[33]

Intentional fallacy[edit]

Sometimes a speaker or writer uses a fallacy intentionally; in any context, including academic debate, a conversation among friends, political discourse, advertising, or for comedic purposes, 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:[34]

  1. Diverting the argument to unrelated issues with a red herring (Ignoratio elenchi)
  2. Insulting someone's character (argumentum ad hominem)
  3. Assume the conclusion of an argument, a kind of circular reasoning, also called "begging the question" (petitio principi)
  4. Making jumps in logic (non-sequitur)
  5. Identifying a false cause and effect (post hoc ergo propter hoc)
  6. Asserting that everyone agrees (argumentum ad populum, bandwagoning)
  7. Creating a "false dilemma" ("either-or fallacy") in which the situation is oversimplified
  8. Selectively using facts (card-stacking)
  9. Making false or misleading comparisons (false equivalence and false analogy)
  10. Generalizing quickly and sloppily (hasty generalization)

In humor, errors of reasoning are used for comical purposes. Groucho Marx used fallacies of amphiboly, for instance, to make ironic statements; Gary Larson and Scott Adams employed fallacious reasoning in many of their 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.[35]

Assessment — pragmatic theory[edit]

According to the pragmatic theory,[36] a fallacy can in some instances be an error a fallacy, use of a heuristic (short version of an argumentation scheme) to jump to a conclusion. However, even more worryingly, in other instances it is a tactic or ploy used inappropriately in argumentation to try to get the best of a speech part unfairly. There are always two parties to an argument containing a fallacy — the perpetrator and the intended victim. The dialogue framework required to support the pragmatic theory of fallacy is built on the presumption that argumentative dialogue has both an adversarial component and a collaborative component. A dialogue has individual goals for each participant, but also collective (shared) goals that apply to all participants. A fallacy of the second kind is seen as more than simply violation of a rule of reasonable dialogue, it is also a deceptive tactic of argumentation, based on sleight-of-hand. Aristotle explicitly compared contentious reasoning to unfair fighting in athletic contest, but the roots of the pragmatic theory go back even further in history to the Sophists. The pragmatic theory finds its roots in the Aristotelian conception of a fallacy as a sophistical refutation, but also supports the view that many of the types of arguments traditionally labelled as fallacies are in fact reasonable techniques of argumentation that can be used, in many cases, to support legitimate goals of dialogue. Hence on the pragmatic approach, each case needs to analyzed individually, to determine by the textual evidence whether the argument is fallacious or reasonable.

See also[edit]


  1. ^ van Eemeren, Frans; Garssen, Bart; Meuffels, Bert (2009). Fallacies and Judgments of Reasonablene Empirical Research Concerning the Pragma-Dialectical Discussion Rules. Dordrecht: Springer. doi:10.1007/978-90-481-2614-9. ISBN 978-90-481-2613-2. 
  2. ^ a b c Harry J. Gensler, The A to Z of Logic (2010:p74). Rowman & Littlefield, ISBN 9780810875968
  3. ^ Woods, John (2004). The Death of Argument. Applied Logic Series. 32. pp. 3–23. ISBN 9789048167005. 
  4. ^ Bustamente, Thomas; Dahlman, Christian, eds. (2015). Argument types and fallacies in legal argumentation. Heidelberg: Springer International Publishing. p. x. ISBN 978-3-319-16147-1. 
  5. ^ "Informal Fallacies, Northern Kentucky University". Retrieved 2013-09-10. 
  6. ^ Dowden, Bradley. "Fallacy". Internet Encyclopedia of Philosophy. Retrieved 17 February 2016. 
  7. ^ McMullin, R, (2000) The New Handbook of Cognitive Therapy Techniques. New York: W. W. Norton & Company Ltd
  8. ^ McMurtry, John (December 1990). "The mass media: An analysis of their system of fallacy". Interchange. 21 (4): 49–66. doi:10.1007/BF01810092. Retrieved 7 March 2018. 
  9. ^ DeLancey, Craig, Ph.D. "Evaluating Arguments—Distinguishing between reasonable and fallacious tactics" (PDF). oswego.edu. self-published. Retrieved 7 March 2018. 
  10. ^ Pirie, Madsen (2006). How to Win Every Argument: The Use and Abuse of Logic. A&C Black. p. 46. ISBN 978-0-8264-9006-3. Retrieved 10 September 2015. 
  11. ^ "fallacy". Encyclopedia Brittanica. Encyclopedia Brittanica. Retrieved 13 June 2017. 
  12. ^ Frans, van Eemeren; Bart, Garssen; Bert, Meuffels (2009). "1". Fallacies and judgements of reasonableness, Empirical Research Concerning the Pragma-Dialectical Discussion Rules. Dordrecht: Springer Science+Business Media B.V. p. 2. ISBN 978-90-481-2613-2. 
  13. ^ "Aristotle's original 13 fallacies". The Non Sequitur. Retrieved 2013-05-28. 
  14. ^ "Aristotle's 13 fallacies". www.logiclaw.co.uk. Retrieved 2017-12-12. 
  15. ^ "PHIL 495: Philosophical Writing (Spring 2008), Texas A&M University". Archived from the original on 2008-09-05. Retrieved 2013-09-10. 
  16. ^ Frans, van Eemeren; Bart, Garssen; Bert, Meuffels (2009). "1". Fallacies and judgements of reasonableness, Empirical Research Concerning the Pragma-Dialectical Discussion Rules. Dordrecht: Springer Science+Business Media B.V. p. 3. ISBN 978-90-481-2613-2. 
  17. ^ Frans, van Eemeren; Bart, Garssen; Bert, Meuffels (2009). "1". Fallacies and judgements of reasonableness, Empirical Research Concerning the Pragma-Dialectical Discussion Rules. Dordrecht: Springer Science+Business Media B.V. p. 4. ISBN 978-90-481-2613-2. 
  18. ^ 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.
  19. ^ Coffey, P. (1912). The Science of Logic. Longmans, Green, and Company. p. 302. LCCN 12018756. Retrieved 2016-02-22. 
  20. ^ 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. 
  21. ^ Kelly, David James (1994). The Art of Reasoning. W.W. Norton & Company. ISBN 0-393-96466-3. 
  22. ^ Copi, Irving M.; Cohen, Carl (2005). Introduction to Logic (12 ed.). Pearson Education, Inc. ISBN 0-13-189834-5.  p.125
  23. ^ "The Most Common Logical Fallacies". www.webpages.uidaho.edu. Retrieved 2017-12-12. 
  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. Archived from the original on 30 October 2013. Retrieved 29 October 2013. 
  25. ^ Schiappa, Edward (1991). Protagoras and Logos: A Study in Greek Philosophy and Rhetoric. Columbia, SC: University of South Carolina Press. ISBN 0872497585. 
  26. ^ Protagoras (1972). The Older Sophists. Indianapolis, IN: Hackett Publishing Co. ISBN 0872205568. 
  27. ^ a b Meho, Lokman I. (2007). "The Rise and Rise of Citation Analysis" (PDF). Physics World. Indiana University. January: 32–36. Retrieved October 28, 2013. 
  28. ^ Jensen, Michael (June 15, 2007). Riley, Michael G., ed. "The New Metrics of Scholarly Authority". The Chronicle of Higher Education. The Chron. ISSN 0009-5982. OCLC 1554535. Retrieved 28 October 2013. 
  29. ^ a b Baveye, Phillippe C. (2010). "Sticker Shock and Looming Tsunami: The High Cost of Academic Serials in Perspective". Journal of Scholarly Publishing. University of Toronto Press. 41 (2): 191–215. doi:10.1353/scp.0.0074. 
  30. ^ National Communication Journal (2013). Impact Factors, Journal Quality, and Communication Journals: A Report for the Council of Communication Associations (PDF). Washington, D.C.: National Communication Association. Archived from the original (PDF) on April 4, 2016. Retrieved 2016-02-22. 
  31. ^ Gafield, Eugene (1993). "What Citations Tell us About Canadian Research". Canadian Journal of Library and Information Science. 18 (4): 34. 
  32. ^ Stein, Zachary (October 2008). "Myth Busting and Metric Making: Refashioning the Discourse about Development". Integral Leadership Review. 8 (5). Archived from the original on October 30, 2013. Retrieved October 28, 2013. 
  33. ^ Allen, Henry L. (1997). "Faculty Workload and Productivity: Ethnic and Gender Disparities" (PDF). NEA 1997 Almanac of Higher Education: 39. Retrieved October 29, 2013. 
  34. ^ Shewan, Edward (2003). "Soundness of Argument". Applications of Grammar: Principles of Effective Communication (2nd ed.). Christian Liberty Press. ISBN 1-930367-28-7. Retrieved February 22, 2016. 
  35. ^ Boyer, Web; Stoddard, Samuel. "How to Be Persuasive". Rink Works. Retrieved December 5, 2012. 
  36. ^ Walton, Douglas N. (1995). A Pragmatic Theory of Fallacy. Tuscaloosa: University of Alabama Press. p. 324. ISBN 9780817307981. 
  37. ^ Damer, T. Edward; Rudinow, J.; Barry, V. E.; Munson, R.; Black, A.; Salmon, M. H.; Cederblom, J.; Paulsen, D.; Epstein, R. L.; Kernberger, C.; others (2009), Attacking Faulty Reasoning: A Practical Guide to Fallacy-free Arguments (6th ed.), Wadsworth, ISBN 978-0-495-09506-4, retrieved 2016-02-24 

Further reading[edit]

  • C. L. Hamblin, Fallacies, Methuen London, 1970. reprinted by Vale Press in 1998 as ISBN 0-916475-24-7.
  • Hans V. Hansen; Robert C. Pinto (1995). Fallacies: classical and contemporary readings. Penn State Press. ISBN 978-0-271-01417-3. 
  • Frans van Eemeren; Bart Garssen; Bert Meuffels (2009). Fallacies and Judgments of Reasonableness: Empirical Research Concerning the Pragma-Dialectical Discussion. Springer. ISBN 978-90-481-2613-2. 
  • Douglas N. Walton, Informal logic: A handbook for critical argumentation. Cambridge University Press, 1989.
  • Douglas, Walton (1987). Informal Fallacies. Amsterdam: John Benjamins. 
  • Walton, Douglas (1995). A Pragmatic Theory of Fallacy. Tuscaloosa: University of Alabama Press. 
  • Walton, Douglas (2010). "Why Fallacies Appear to Be Better Arguments than They Are". Informal Logic. 30 (2): 159–184. 
  • John Woods (2004). The death of argument: fallacies in agent based reasoning. Springer. ISBN 978-1-4020-2663-8. 
  • Fearnside, W. Ward and William B. Holther, Fallacy: The Counterfeit of Argument, 1959.
  • Vincent F. Hendricks, Thought 2 Talk: A Crash Course in Reflection and Expression, New York: Automatic Press / VIP, 2005, ISBN 87-991013-7-8
  • D. H. Fischer, Historians' Fallacies: Toward a Logic of Historical Thought, Harper Torchbooks, 1970.
  • Warburton Nigel, Thinking from A to Z, Routledge 1998.
  • Sagan, Carl, "The Demon-Haunted World: Science As a Candle in the Dark". Ballantine Books, March 1997 ISBN 0-345-40946-9, 480 pgs. 1996 hardback edition: Random House, ISBN 0-394-53512-X, xv+457 pages plus addenda insert (some printings). Ch.12.

Historical texts[edit]

External links[edit]