formal fallacy

{{main|List of fallacies}}

{{More citations needed section|date=May 2010}}

"Some of your key evidence is missing, incomplete, or even faked! That proves I'm right!"{{cite web|title=Master List of Logical Fallacies|url=http://utminers.utep.edu/omwilliamson/ENGL1311/fallacies.htm|website=utminers.utep.edu}}

"The vet can't find any reasonable explanation for why my dog died. See! See! That proves that you poisoned him! There’s no other logical explanation!"{{cite book|author1=Daniel Adrian Doss|author2=William H. Glover Jr.|author3=Rebecca A. Goza |author4=Michael Wigginton Jr. |title=The Foundations of Communication in Criminal Justice Systems|url=https://books.google.com/books?id=qqrNBQAAQBAJ&pg=PA66|access-date=21 May 2016|date=17 October 2014|publisher=CRC Press|isbn=978-1-4822-3660-6|page=66}}

File:Logical fallacy.svg illustrating a fallacy:

Statement 1: Most of the green is touching the red.

Statement 2: Most of the red is touching the blue.

Logical fallacy: Since most of the green is touching red, and most of the red is touching blue, most of the green must be touching blue. This, however, is a false statement.]]

In the strictest sense, a logical fallacy is the incorrect application of a valid logical principle or an application of a nonexistent principle:

1. Most Rimnars are Jornars.
2. Most Jornars are Dimnars.
3. Therefore, most Rimnars are Dimnars.

This is fallacious.

Indeed, there is no logical principle that states:

1. For some x, P(x).
2. For some x, Q(x).
3. Therefore, for some x, P(x) and Q(x).

An easy way to show the above inference as invalid is by using Venn diagrams. In logical parlance, the inference is invalid, since under at least one interpretation of the predicates it is not validity preserving.

People often have difficulty applying the rules of logic. For example, a person may say the following syllogism is valid, when in fact it is not:

1. All birds have beaks.
2. That creature has a beak.
3. Therefore, that creature is a bird.

"That creature" may well be a bird, but the conclusion does not follow from the premises. Certain other animals also have beaks, for example: an octopus and a squid both have beaks, some turtles and cetaceans have beaks. Errors of this type occur because people reverse a premise.{{cite book|last=Wade|first=Carole|author2=Carol Tavris|others=Laura Pearson|title=Psychology|editor=Donna DeBenedictis|publisher=Harper and Row|location=New York|year=1990|edition=2|pages=[https://archive.org/details/psychology00wade/page/287 287–288]|chapter=Eight|isbn=0-06-046869-6|chapter-url-access=registration|chapter-url=https://archive.org/details/psychology00wade/page/287}} In this case, "All birds have beaks" is converted to "All beaked animals are birds." The reversed premise is plausible because few people are aware of any instances of beaked creatures besides birds—but this premise is not the one that was given. In this way, the deductive fallacy is formed by points that may individually appear logical, but when placed together are shown to be incorrect.

{{main|Non sequitur (literary device)}}

{{see also|Derailment (thought disorder)}}

In everyday speech, a non sequitur is a statement in which the final part is totally unrelated to the first part, for example:

{{quote|Life is life and fun is fun, but it's all so quiet when the goldfish die.|West with the Night|Beryl MarkhamQuoted in {{cite book|last=Hindes|first=Steve|title=Think for Yourself!: an Essay on Cutting through the Babble, the Bias, and the Hype|year=2005|publisher=Fulcrum Publishing|isbn=1-55591-539-6|pages=86|url=https://books.google.com/books?id=h2HHJeVTrU8C&pg=PA86|access-date=2011-10-04}}}}

{{Portal|Philosophy|Psychology}}

{{Div col}}

• {{annotated link|List of fallacies}}
• {{annotated link|Apophasis}}
• {{annotated link|Cognitive bias}}
• {{annotated link|Demagogue}}
• {{annotated link|Fallacies of definition}}
• {{annotated link|False statement}}
• {{annotated link|Mathematical fallacy|aka=Invalid proof}}
• {{annotated link|Modus tollens|Modus tollens}}
• {{annotated link|Paradox}}
• {{annotated link|Relevance logic}}
• {{annotated link|Scientific misconceptions}}
• {{annotated link|Sophist}}
• {{annotated link|Soundness}}
• Subverted support – Logical fallacy of explanation

{{div col end}}

{{Notelist}}

{{reflist}}

;Bibliography

{{Refbegin}}

• Aristotle, [https://web.archive.org/web/20061004164921/http://etext.library.adelaide.edu.au/a/aristotle/sophistical/ On Sophistical Refutations], De Sophistici Elenchi.
• William of Ockham, Summa of Logic (ca. 1323) Part III.4.
• John Buridan, Summulae de dialectica Book VII.
• Francis Bacon, the doctrine of the idols in Novum Organum Scientiarum, [http://fly.hiwaay.net/%7Epaul/bacon/organum/aphorisms1.html Aphorisms concerning The Interpretation of Nature and the Kingdom of Man, XXIIIff] {{Webarchive|url=https://web.archive.org/web/20200214120354/http://fly.hiwaay.net/~paul/bacon/organum/aphorisms1.html |date=2020-02-14 }}.
• [https://www.gutenberg.org/files/10731/10731-8.txt The Art of Controversy] | [http://coolhaus.de/art-of-controversy/ Die Kunst, Recht zu behalten – The Art Of Controversy (bilingual)], by Arthur Schopenhauer
• John Stuart Mill, [http://www.la.utexas.edu/research/poltheory/mill/sol/ A System of Logic – Raciocinative and Inductive]. [http://www.la.utexas.edu/research/poltheory/mill/sol/sol.b05.c07.html Book 5, Chapter 7, Fallacies of Confusion].
• C. L. Hamblin, [http://www.ditext.com/hamblin/fallacies.html Fallacies]. Methuen London, 1970.
• Fearnside, W. Ward and William B. Holther, [http://www.ditext.com/fearnside/fallacy.html 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.
• Douglas N. Walton, Informal logic: A handbook for critical argumentation. Cambridge University Press, 1989.
• F. H. van Eemeren and R. Grootendorst, Argumentation, Communication and Fallacies: A Pragma-Dialectical Perspective, Lawrence Erlbaum and Associates, 1992.
• 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 pp. 1996 hardback edition: Random House, {{ISBN|0-394-53512-X}}

{{Refend}}

{{Wikiversity|Recognizing Fallacies}}

{{Commons category|Formal fallacies}}

{{Fallacies}}

{{Authority control}}

Category:Barriers to critical thinking

Category:Deductive reasoning

Category:Philosophical logic