Formal Fallacies

Assumes that if ‘If A then B’ is true, then ‘Not A’ implies ‘Not B’, which is invalid.

A syllogism error where the middle term is not distributed, leaving the major and minor terms possibly unrelated.

A syllogism error where the major term is undistributed in the premises but distributed in the conclusion.

A syllogism error where the minor term is undistributed in the premises but distributed in the conclusion.

Introduces a fourth term in a syllogism, breaking the required three-term structure and invalidating the inference.

Confuses possibility, probability, and necessity, or shifts between them illegitimately in an argument.

Illegitimately swaps universal and existential quantifiers, changing meaning and invalidating the inference.

Assumes that if a result occurs, the only cause must be a specific prior condition.