Two Logical arguments in Comic Strips

The sensible one is a fallacy, the crazy one is valid

Garfield tries to use modus tollens as a Reductio ad Absurdum, but he makes a logical error, confusing John’s claim of necessity for a claim of sufficiency. Even if John’s arrival was necessary for an event to be a party, that doesn’t imply that his arrival is sufficient to make an event a party. Garfield’s inference would have worked only if John had said “It’s always a party when I arrive.” As it stands, John is only claiming that All Parties are events that he attends. He is not claiming that all events he attends are parties.

Garfield’s inference relies on the logical fallacy of denying the antecedent. If I have not arrived, it is not a party. I have arrived, therefore it is a party. But John does not make that inference. He is just asserting a conditional statement as a fact: If you claim any particular convocation is a party, then your claim will be falsified if he is not there. Garfield could have refuted this conditional claim with modus tollens, by pointing out that John was not in Times Square on New Years Eve, or at the White House Easter Egg hunt, and yet those were still parties. But that wouldn’t have been funny.