How does affirmation of the consequent differ from denying the antecedent?

Affirmation of the consequent and denying the antecedent are both formal fallacies that involve invalid deductive reasoning based on a conditional statement ("If p, then q"). They differ in which part of the premise is manipulated to reach an erroneous conclusion.12

Affirmation of the Consequent

This fallacy occurs when one assumes that because the consequent (q) is true, the antecedent (p) must also be true.31
* Structure: If p, then q; q; therefore, p.12
* Example: "If Amos was a prophet, then he had a social conscience; he had a social conscience; hence, Amos was a prophet".1

Denying the Antecedent

This fallacy occurs when one assumes that because the antecedent (p) is false, the consequent (q) must also be false.14
* Structure: If p, then q; not-p; therefore, not-q.12
* Example: "If George is a man of good faith, he can be entrusted with this office; but George is not a man of good faith; therefore, George cannot be entrusted with this office".1