Is modus ponens a fallacy?

Modus ponens is not a logical fallacy; it is a valid form of deductive reasoning. Also known as “affirming the antecedent,” it employs a straightforward logical structure:

  • If P, then Q.
  • P.
  • Therefore, Q.

However, flawed attempts at forming a syllogism often result in formal logical fallacies, such as denying the antecedent, which resembles modus ponens in form but fails to provide logical certainty:

  • If P, then Q.
  • Not P.
  • Therefore, not Q.

Although the two arguments look similar, denying the antecedent is an invalid form of argument.