Fallacy 4 of 4

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Fallacy of Four Terms

F014Formal - Syllogistic Logic

Also known as: Quaternio Terminorum

Difficulty 1/10Low-Medium LoadUncommon

Definition

A categorical syllogism that appears to have three terms but actually has four due to equivocation.

Why Invalid

A valid categorical syllogism must have exactly three terms used consistently. Four terms means the middle term doesn't actually connect the major and minor terms.

Examples

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  1. Count distinct terms in syllogism
  2. Check for equivocation (same word, different meanings)
  3. Verify each term used consistently
  • Not recognizing subtle equivocations
  • Confusing with other syllogistic fallacies
EquivocationFallacy of the Undistributed Middle

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