Formal syllogistic fallacies

Syllogistic fallacies – logical fallacies that occur in syllogisms.

• Affirmative conclusion from a negative premise (illicit negative) – when a categorical syllogism has a positive conclusion, but at least one negative premise.[9]
• Fallacy of exclusive premises – a categorical syllogism that is invalid because both of its premises are negative.[9]
• Fallacy of four terms (quaternio terminorum) – a categorical syllogism that has four terms.[10]
• Illicit major – a categorical syllogism that is invalid because its major term is not distributed in the major premise but distributed in the conclusion.[9]
• Illicit minor – a categorical syllogism that is invalid because its minor term is not distributed in the minor premise but distributed in the conclusion.[9]
• Negative conclusion from affirmative premises (illicit affirmative) – when a categorical syllogism has a negative conclusion but affirmative premises.[9]
• Fallacy of the undistributed middle – the middle term in a categorical syllogism is not distributed.[11]