Logical fallacy

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A logical fallacy can be any one of a number of formal or informal mistakes in a deductive proof.
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{{wikipedia|color=#E9FFDA;}}
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A '''logical fallacy''' can be any one of a number of formal or informal mistakes in a [[deductive proof]].
  
 
Note that an argument can be fallacious but still correct.  For instance:
 
Note that an argument can be fallacious but still correct.  For instance:
 
 
# All fish live in the water.
 
# All fish live in the water.
 
# All trout live in the water.
 
# All trout live in the water.
 
# Therefore all trout are fish.
 
# Therefore all trout are fish.
  
The premises are accurate and the conclusion is accurate, but it the conclusion is not a valid inference from the premises.  To see why, notice that we could use identical reasoning to prove that "all whales are fish."
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The [[premise]]s are [[true]] and the conclusion is true, but the conclusion is not a [[valid]] [[inference]] from the premises.  To see why, notice that we could use identical reasoning to prove that "all whales are fish" (of course, whales are mammals not fish).
 
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Likewise, an argument can be logically sound but still wrong.
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Likewise, an argument can be logically [[valid]] but still wrong:
 
# All bugs are insects.
 
# All bugs are insects.
 
# All spiders are bugs.
 
# All spiders are bugs.
 
# Therefore, all spiders are insects.
 
# Therefore, all spiders are insects.
  
Some of the premises are factually incorrect, and the conclusion is also untrue.  However, the conclusion is an accurate deduction based on those premises.
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One of the premises is factually incorrect (which one depends on your definition of the word ''bug'') and the conclusion is also untrue.  However, the conclusion is an accurate deduction based on these premises.  Validity and soundness are also discussed in the article [[Validity vs. soundness]].
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For examples of logical fallacies, visit the [[:Category:Logical fallacies|logical fallacies category]].
  
==Examples of Fallacies==
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==Literature==
Here are a few examples for future articles:
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*''[[How To Win Every Argument]]'' by Madsen Pirie, ISBN 0-8264-9006-9
  
* [[Appeal to emotion]]
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==External links==
* [[Ad hominem]]
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*[http://www.infidels.org/library/modern/mathew/logic.html Logic & Fallacies: Constructing a Logical Argument] at [[The Secular Web]]
* [[Post hoc ergo propter hoc]]
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There are many more in the logical fallacies category.
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{{Logical fallacies}}
  
[[Category: Logical fallacies]]
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[[Category:Logical fallacies|*]]
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[[Category:Logic]]

Revision as of 08:39, 19 December 2009

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For more information, see the Wikipedia article:

A logical fallacy can be any one of a number of formal or informal mistakes in a deductive proof.

Note that an argument can be fallacious but still correct. For instance:

  1. All fish live in the water.
  2. All trout live in the water.
  3. Therefore all trout are fish.

The premises are true and the conclusion is true, but the conclusion is not a valid inference from the premises. To see why, notice that we could use identical reasoning to prove that "all whales are fish" (of course, whales are mammals not fish).

Likewise, an argument can be logically valid but still wrong:

  1. All bugs are insects.
  2. All spiders are bugs.
  3. Therefore, all spiders are insects.

One of the premises is factually incorrect (which one depends on your definition of the word bug) and the conclusion is also untrue. However, the conclusion is an accurate deduction based on these premises. Validity and soundness are also discussed in the article Validity vs. soundness.

For examples of logical fallacies, visit the logical fallacies category.

Literature

External links


v · d Logical fallacies
v · d Formal fallacies
Propositional logic   Affirming a disjunct · Affirming the consequent · Argument from fallacy · False dilemma · Denying the antecedent
Quantificational logic   Existential fallacy · Illicit conversion · Proof by example · Quantifier shift
Syllogistic   Affirmative conclusion from a negative premise · Exclusive premises · Necessity · Four-term Fallacy · Illicit major · Illicit minor · Undistributed middle
v · d Faulty generalisations
General   Begging the question · Gambler's fallacy · Slippery slope · Equivocation · argumentum verbosium
Distribution fallacies   Fallacy of composition · Fallacy of division
Data mining   Cherry picking · Accident fallacy · Spotlight fallacy · Hasty generalization · Special pleading
Causation fallacies   Post hoc ergo propter hoc · Retrospective determinism · Suppressed correlative · Wrong direction
Ontological fallacies   Fallacy of reification · Pathetic fallacy · Loki's Wager
v · d False relevance
Appeals   Appeal to authority · Appeal to consequences · Appeal to emotion · Appeal to motive · Appeal to novelty · Appeal to tradition · Appeal to pity · Appeal to popularity · Appeal to poverty · Appeal to spite · Appeal to wealth · Sentimental fallacy · Argumentum ad baculum
Ad hominem   Ad hominem abusive · Reductio ad Hitlerum · Judgmental language · Straw man · Tu quoque · Poisoning the well
Genetic Fallacies   Genetic fallacy · Association fallacy · Appeal to tradition · Texas sharpshooter fallacy
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