Fallacies – Rapid Review

What is a Fallacy?

  • A fallacy = an argument containing a mistake in reasoning.
  • Two broad kinds:
    • Fallacies of Relevance → premises are logically irrelevant to conclusion.
    • Fallacies of Insufficient Evidence → premises relevant but give inadequate support.

Relevance Basics

  • Statement P is positively relevant to Q if it gives a reason for Q being true.
  • Negatively relevant if it gives a reason for Q being false.
  • Logically irrelevant if it gives no reason either way.

Fallacies of Relevance (10)

  • Personal Attack (Ad Hominem) – reject claim by attacking the person.
  • Attacking the Motive – dismiss claim because speaker has self-interest.
  • Look Who’s Talking (Tu Quoque) – reject advice as hypocritical.
  • Two Wrongs Make a Right – justify wrongdoing by citing other wrongs.
  • Scare Tactics – use threats/fear instead of reasons.
  • Appeal to Emotion (Pity / Ad Populum) – rely on feelings, not evidence.
  • Bandwagon (Peer Pressure) – “everyone does/believes it” ⇒ you should too.
  • Straw Man – distort opponent’s view, attack the distortion.
  • Red Herring – divert with irrelevant issue, claim original is settled.
  • Equivocation – shift meaning of key word/phrase mid-argument.
  • Begging the Question – premise merely restates conclusion (circular).

Fallacies of Insufficient Evidence (10)

  • False Authority – cite unqualified or unreliable source.
  • Appeal to Ignorance – “not proved false/true, therefore true/false.”
  • False Dilemma – restrict to 2 (or few) options when more exist.
  • Loaded Question – single question embeds unwarranted assumption.
  • False Cause – assume causal link from mere correlation.
  • Hasty Generalization – general rule from biased or small sample.
  • Slippery Slope – claim harmless step inevitably leads to disaster.
  • Weak Analogy – compare items lacking relevant similarity.
  • Inconsistency – advance mutually contradictory claims.

Quick Detection Tips

  • Check source competence & bias (False Authority).
  • Separate emotional language from factual premises.
  • List alternatives; if more than the arguer offers → possible False Dilemma.
  • Ask whether causal claim rests on controlled evidence (False Cause).
  • For analogies: list key similarities/differences; irrelevant ones → Weak Analogy.
  • Look for hidden premises that duplicate conclusion (Begging the Question).

Memory Card: 20 Common Fallacies

  • Relevance: Ad Hominem, Motive, Tu Quoque, Two Wrongs, Scare, Emotion, Bandwagon, Straw Man, Red Herring, Equivocation, Beg Question.
  • Insufficient Evidence: False Authority, Ignorance, False Dilemma, Loaded Q, False Cause, Hasty Gen., Slippery Slope, Weak Analogy, Inconsistency.