Illicit major

Formal fallacies → Syllogistic / quantification

Illicit major is when you use "all" and "no" in a way that doesn't actually connect the terms, so the conclusion doesn't follow from the two facts you gave. The middle term isn't used in a way that links the other two terms correctly. It feels like a proper syllogism, but the distribution of "all" and "no" across the premises doesn't support the conclusion. The steps don't add up.

Examples

  • All dogs are mammals. No cats are dogs. So no cats are mammals.

  • All employees must wear badges. No visitors are employees. So no visitors must wear badges.

  • All birds have feathers. No bats are birds. So no bats have feathers.

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