Logical Fallacy of the Week, Week 11: Affirmative Conclusion From a Negative Premise

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We will now explore formal syllogistic fallacies - Syllogistic fallacies are logical fallacies that occur in syllogisms, and we will state with:

• Affirmative conclusion from a negative premise (illicit negative): when a categorical syllogism has a positive conclusion, but at least one negative premise.
• Affirmative conclusion from a negative premise is a logical fallacy that is committed when a categorical syllogism has a positive conclusion, but one or two negative premises.
• For example:
• No fish are dogs, and no dogs can fly, therefore all fish can fly.
• The only thing that can be properly inferred from these premises is that some things that are not fish cannot fly, provided that dogs exist.
• Or:
• We don't read that trash. People who read that trash don't appreciate real literature. Therefore, we appreciate real literature.
• This could be illustrated mathematically as - If A ⊄ B and B ⊄ C then A ⊂ C.
• It is a fallacy because any valid forms of categorical syllogism that assert a negative premise must have a negative conclusion.

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