Fallacies and Critical Thinking
Two families
A formal fallacy violates a rule of inference (affirming the consequent, denying the antecedent). An informal fallacy fails through relevance, ambiguity or unwarranted assumption.
- Relevance: ad hominem, appeal to force, appeal to pity, appeal to the populace, appeal to unqualified authority, appeal to ignorance, red herring.
- Ambiguity: equivocation, amphiboly, accent, composition, division.
- Presumption: begging the question, complex question, false dilemma, false cause (post hoc), hasty generalization, accident, straw man, slippery slope.
Critical thinking
Identify the conclusion, lay out the premises, test relevance and sufficiency, and check for loaded language. A fallacy is a defect in the reasoning; the conclusion may still happen to be true.
Worked example
“Don’t listen to her argument about the exam pattern - she failed last year.” This attacks the arguer’s circumstances, not the argument: ad hominem. Rebut it by asking whether her premises and inference are correct.
Traps that cost marks
Many candidates name a fallacy without explaining why it applies - the explanation earns the marks. Distinguish accident (applying a general rule to an exceptional case) from hasty generalization (generalising from too few cases), and post hoc (mere temporal succession) from genuine causation. Begging the question means a premise assumes the conclusion, not merely that the point is obvious.