Formal fallacy
A flaw in logical structure making an argument invalid.
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A formal fallacy is a deductive argument that is invalid because its logical structure contains an error in reasoning.[1][2] The error lies in the sequence of deduction, not in the truth of the premises.[2] An argument that commits a formal fallacy can have all true premises yet still produce a false conclusion, because the deduction has gone wrong.[2][1]
Quick Facts
- Field
- Logic and philosophy
- Known for
- Pattern of reasoning with a flaw in logical structure
- Related concept
- Propositional logic
- Common example
- All birds have beaks
- that creature has a beak
- therefore, that creature is a bird
- Special case
- Mathematical fallacy
Facts from the source article.
Key facts and history
Labossiere’s 1995 "Description of Fallacies" defines a fallacy generally as an error in reasoning.[1] A common example of a formal fallacy is reversing a premise, such as converting "All birds have beaks" into "All beaked creatures are birds".[3] The conclusion that a beaked creature is a bird does not follow from the original premises.[3] A deductive fallacy is an invalid argument; it is possible for such an argument to have all true premises and a false conclusion, which means the premises do not offer the required level of support.[1]
Propositional connectives are logical operators that help decide whether a sentence is true.[2] Errors of this type happen when people reverse a premise, for example converting "All birds have beaks" into "All beaked creatures are birds."[3]
What the cited sources add
Labossiere’s 1995 work explains that an inductive fallacy is less formal than a deductive fallacy.[1] Gensler’s 2010 "The A to Z of Logic" is the source for the statement that propositional logic concerns sentence meanings and relationships.[4][5] Labossiere gives a deductive fallacy example with a conditional premise: "If Portland is the capital of Maine, then it is in Maine."[1] Labossiere also provides an inductive fallacy example: "Having just arrived in Ohio, I saw a white squirrel."[1]
References
- Labossiere, "Description of Fallacies", Nizkor Project, 1995. facts only, no text reused. nizkor.org
- Wikipedia, "Formal fallacy" (CC BY-SA 4.0), which cites: Labossiere, "Description of Fallacies", Nizkor Project, 1995 (we also read that source) en.wikipedia.org
- Wikipedia, "Formal fallacy" (CC BY-SA 4.0), which cites: Wade, "Psychology", Harper and Row, 1990, p. 287–288 (we also read that source) en.wikipedia.org
- Wikipedia, "Formal fallacy" (CC BY-SA 4.0), which cites: Gensler, "The A to Z of Logic", Rowman & Littlefield, 2010, p. 74 (we also read that source) en.wikipedia.org
- Open Library record, ISBN 9780810875968 ("The A To Z Of Logic"). CC0 (metadata); book content not read. openlibrary.org
Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Formal fallacy (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.
More in Philosophical Concepts And Theories
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Formal fallacy (CC BY-SA 4.0).
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