Illicit major

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The Illicit Major fallacy is a logical fallacy that occurs when an argument is based on a syllogism but does not maintain the scope defined in the major (first) premise when forming the conclusion.

  1. All A are B
  2. No C is an A
  3. No C is a B

The syllogism fails because the conclusion attempts to make a claim about all B (if no C is B then no B can be C) even though the major premise only applies to some B (all A may be B but some B may not be A). When there is a discrepancy between the scopes used in the major premise and the conclusion the argument has an illicit major.


  1. Every Catholic is a Christian
  2. No Baptist is a Catholic
  3. Therefore no Baptist is a Christian

In the above argument the major premise defines Catholics as a subset of Christians and the minor premise defines a relationship between Baptists and that subset. The conclusion then attempts to relate Baptists to the entire set of Christians instead of the Catholic subset defined in the major premise and that makes the argument invalid.

v · d Logical fallacies
v · d Formal fallacies
Propositional logic   Affirming a disjunct · Affirming the consequent · Argument from fallacy · False dilemma · Denying the antecedent
Quantificational logic   Existential fallacy · Illicit conversion · Proof by example · Quantifier shift
Syllogistic   Affirmative conclusion from a negative premise · Exclusive premises · Necessity · Four-term fallacy · Illicit major · Illicit minor · Undistributed middle

v · d Faulty generalisations
General   Begging the question · Gambler's fallacy · Slippery slope · Equivocation · argumentum verbosium
Distribution fallacies   Fallacy of composition · Fallacy of division
Data mining   Cherry picking · Accident fallacy · Spotlight fallacy · Hasty generalization · Special pleading
Causation fallacies   Post hoc ergo propter hoc · Retrospective determinism · Suppressed correlative · Wrong direction
Ontological fallacies   Fallacy of reification · Pathetic fallacy · Loki's Wager
v · d False relevance
Appeals   Appeal to authority · Appeal to consequences · Appeal to emotion · Appeal to motive · Appeal to novelty · Appeal to tradition · Appeal to pity · Appeal to popularity · Appeal to poverty · Appeal to spite · Appeal to wealth · Sentimental fallacy · Argumentum ad baculum
Ad hominem   Ad hominem abusive · Reductio ad Hitlerum · Judgmental language · Straw man · Tu quoque · Poisoning the well
Genetic Fallacies   Genetic fallacy · Association fallacy · Appeal to tradition · Texas sharpshooter fallacy
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