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  • False Conversion
  • False Dilemma
  • False Effect
  • Far-Fetched Hypothesis
  • Faulty Comparison
  • Gambler’s Fallacy
  • Genetic Fallacy
  • Hasty Generalization
  • Having Your Cake
  • Hedging
  • Historian’s Fallacy
  • Homunculus Fallacy
  • Hypnotic Bait and Switch
  • Hypothesis Contrary to Fact
  • The Fallacies: If–Mu
  • If-By-Whiskey
  • Illicit Contraposition
  • Illicit Major
  • Illicit Minor
  • Illicit Substitution of Identicals
  • Inconsistency
  • Inflation of Conflict
  • Jumping to Conclusions
  • Just Because Fallacy*
  • Just In Case Fallacy
  • Least Plausible Hypothesis
  • Limited Depth
  • Limited Scope
  • Logic Chopping
  • Ludic Fallacy
  • Lying with Statistics
  • Magical Thinking
  • Meaningless Question
  • Misleading Vividness
  • Missing Data Fallacy*
  • Modal (Scope) Fallacy
  • Moralistic Fallacy
  • Moving the Goalposts
  • Multiple Comparisons Fallacy
  • The Fallacies: Na–Ri
  • Naturalistic Fallacy
  • Negating Antecedent and Consequent
  • Negative Conclusion from Affirmative Premises
  • Nirvana Fallacy
  • No True Scotsman
  • Non Sequitur
  • Notable Effort
  • Overwhelming Exception
  • Package-Deal Fallacy
  • Poisoning the Well
  • Political Correctness Fallacy
  • Post-Designation
  • Prejudicial Language
  • Proof by Intimidation
  • Proving Non-Existence
  • Quantifier-Shift Fallacy
  • Quantum Physics Fallacy*
  • Questionable Cause
  • Rationalization
  • Red Herring
  • Reductio ad Absurdum
  • Reductio ad Hitlerum
  • Regression Fallacy
  • Reification
  • Relative Privation
  • Retrogressive Causation
  • Rights To Ought Fallacy*
  • The Fallacies: Sc–Wi
  • Scapegoating
  • Selective Attention
  • Self-Sealing Argument
  • Shoehorning
  • Slippery Slope
  • Special Pleading
  • Spiritual Fallacy*
  • Spotlight Fallacy
  • Statement of Conversion
  • Stereotyping
  • Stolen Concept Fallacy
  • Strawman Fallacy
  • Style Over Substance
  • Subjectivist Fallacy
  • Subverted Support
  • Sunk-Cost Fallacy
  • Suppressed Correlative
  • Texas Sharpshooter Fallacy
  • Tokenism
  • Two Wrongs Make a Right
  • Unfalsifiability
  • Unwarranted Contrast
  • Use-Mention Error
  • Weak Analogy
  • Willed Ignorance
  • Wishful Thinking
  • Exclusive Premises

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    (also known as: fallacy of exclusive premises)

    Description: A standard form categorical syllogism that has two negative premises either in the form of  “no X are Y” or “some X are not Y”.

    Logical Form:

    No X are Y.

    Some Y are not Z.

    Therefore, some Z are not X.

     

    No X are Y.

    No Y are Z.

    Therefore, no Z are X.

    Example #1:

    No kangaroos are MMA fighters.

    Some MMA fighters are not Mormons.

    Therefore, some Mormons are not kangaroos.

    Example #2:

    No animals are insects.

    Some insects are not dogs.

    Therefore, some dogs are not animals.

    Example #3:

    No animals are insects.

    No insects are dogs.

    Therefore, no dogs are animals.

    Explanation: Remember why fallacies are so dangerous: because they appear to be good reasoning.  The conclusion in example #1 makes sense, but it does not follow logically -- it is an invalid argument.  Based on the first two premises, there is no way logically to deduce that conclusion.  Now look at examples #2 and #3.  We use the same logical form of the argument, committing the same fallacy, but by changing the terms it is much more clear that something went wrong somewhere, and it did.  This kind of argument, the categorical syllogism, cannot have two negative premises and still be valid.

    Just because the conclusion appears true, it does not mean the argument is valid (or strong, in the case of an informal argument).

    Exception: None.

    Tip: Learn to recognize the forms of formal fallacies, and you will easily spot invalid formal arguments.





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