Which fallacy is present in the argument: If P then Q; Q; Therefore P?

• A. Modus ponens.
• B. Denying the antecedent.
• C. Affirming the antecedent.
• D. Affirming the consequent (fallacy).

Answer: (D)

Conditional statements tie P to Q, but seeing Q does not prove P. Inferring P from Q when the rule is “If P then Q” is the affirming the consequent fallacy. It treats Q as if it were evidence that P must be true, but Q could occur for other reasons as well.

A clear example: If it is raining, the ground is wet. The ground is wet, therefore it is raining. Water could also come from sprinklers or another cause, so you can’t conclude P just from Q.

The valid pattern would be: if P then Q; P; therefore Q. Knowing P leads to Q, but simply knowing Q does not guarantee P.