Formal fallacies

“Formal” fallacies are errors in the form of a logical inference.

• Non sequitur (“it does not follow”)

• Affirming a disjunct
• Affirming the consequent
• Denying a conjunct
• Denying the antecedent

• Affirmative conclusion from a negative premise
• Negative conclusion from affirmative premises
• Fallacy of exclusive premises
• Fallacies of distribution
  • Illicit process (undistributed minor/major)
  • Undistributed middle
• Four-term fallacy
  • Ambiguous middle (term)

• Circular reasoning
• Existential fallacy