Undistributed middle

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* Example 3
* Example 3
:# All fish swim in the ocean.
:# All fish live in water.
:# All whales swim in the ocean.
:# All whales live in water.
:# Therefore, all whales are fish (They're not - they're mammals)
:# Therefore, all whales are fish (They're not - they're mammals)
{{Logical fallacies}}
[[Category:Logical fallacies]]
[[Category:Logical fallacies]]

Revision as of 10:14, 28 April 2011

The Undistributed middle is a fallacy similar to to Equivocation, except that instead of conflating definitions, two different things are equated due to a common middle ground that is misused. The argument is assuming that the set of Object-A that has the middle ground intersects with the set of Object-B that has the same middle ground.


  • Example 1
  1. All cats use air.
  2. All gasoline engines use air.
  3. Therefore, all cats are gasoline engines.
  • Example 2
  1. Science uses the word Theory.
  2. Creationism uses the word Theory.
  3. Thus, Creationism is science.
  • Example 3
  1. All fish live in water.
  2. All whales live in water.
  3. Therefore, all whales are fish (They're not - they're mammals)

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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