Logical Fallacies
Logical Fallacies / Propositional Fallacies

Propositional Fallacies

A propositional fallacy is one where an error in logic takes place due to compound propositions--a proposition is a 'statement'. In order for a compound proposition to have a true value, each component proposition must also be true.

Logic formulas:

  • Affirming a disjunct: A or B; A; therefore not B
  • Affirming the consent: A, then B; B, therefore A
  • Denying the antecedent: If A, then B; not A, therefore not B

Example of Propositional Fallacies

William Shatner is Captain Kirk or he is in Miss Congeniality. William Shatner is in Miss Congeniality. Therefore he is not Captain Kirk.

Alternative Name: Denying the Antecedent